40 The s-Block Elements 40.1 Characteristic Properties of the s-Block Elements 40.2 Variation in Properties of the s-Block Elements 40.3 Variation in.

40 The s-Block Elements 40.1 Characteristic Properties of the s-Block Elements 40.2 Variation in Properties of the s-Block Elements 40.3 Variation in Properties of the Compounds of the s-Block Elements

The s-Block Elements Elements of Groups IA* (the alkali metals) and IIA* (the alkaline earth metals)  constitute the s-block elements  their outermost shell electrons are in the s orbital *Note: In the following, Groups IA and IIA are abbreviated as Groups I and II respectively.

The s-Block Elements The two groups of elements have many similarities
 highly reactive metals  strong reducing agents  form ionic compounds with fixed oxidation states of +1 for Group I elements and +2 for Group II elements

The s-block elements

Group I elements Lithium

Group I elements Sodium

Group I elements Potassium

Group I elements Rubidium

Group I elements Francium

Group I elements Beryllium

Group I elements Magnesium

Group I elements Calcium

Group I elements Strontium

Group I elements Barium

Group I elements Radium

Characteristic Properties of the s-Block Elements
40.1 Characteristic Properties of the s-Block Elements

Some characteristic properties of Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.38) Some characteristic properties of Group I elements Group I element Atomic number Electronic configuration Electronegativity value Oxidation state in compounds Li Na K Rb Cs Fr 3 11 19 37 55 87 [He] 2s1 [Ne] 3s1 [Ar] 4s1 [Kr] 5s1 [Xe] 6s1 [Rn] 7s1 1.0 0.9 0.8 0.7 – +1

Some characteristic properties of Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.38) Some characteristic properties of Group I elements Group I element Oxide formed Hydroxide formed Flame colour Li Na K Rb Cs Fr Li2O Na2O, Na2O2 K2O, K2O2, KO2 Rb2O, Rb2O2, RbO2 Cs2O, Cs2O2, CsO2 – LiOH NaOH KOH RbOH CsOH deep red yellow lilac bluish red blue

Some characteristic properties of Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.38) Some characteristic properties of Group II elements Group II element Atomic number Electronic configuration Electronegativity value Oxidation state in compounds Be Mg Ca Sr Ba Ra 4 12 20 38 56 88 [He] 2s2 [Ne] 3s2 [Ar] 4s2 [Kr] 5s2 [Xe] 6s2 [Rn] 7s2 1.5 1.2 1.0 0.9 – +2

Some characteristic properties of Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.38) Some characteristic properties of Group II elements Group II element Oxide formed Hydroxide formed Flame colour Be Mg Ca Sr Ba Ra BeO MgO CaO SrO, SrO2 BaO, BaO2 – Be(OH)2 Mg(OH)2 Ca(OH)2 Sr(OH)2 Ba(OH)2 bluish red blood-red or crimson blue

Metallic Character All Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.38) Metallic Character All Group I elements  silvery solids and tarnish rapidly in air at room temperature and pressure  stored under paraffin oil or in vacuum-sealed ampoules (to prevent contact with oxygen and water vapour in air)

Metallic Character All Group I elements  weak metallic bonds
40.1 Characteristic Properties of the s-Block Elements (SB p.38) Metallic Character All Group I elements  weak metallic bonds  only one valence electron per atom delocalized into the electron sea for the formation of metallic bonds  soft and can be cut with a knife easily

40.1 Characteristic Properties of the s-Block Elements (SB p.38) Metallic Character All Group I elements  low melting points and boiling points

Sodium is stored under paraffin oil
40.1 Characteristic Properties of the s-Block Elements (SB p.39) sodium Sodium is stored under paraffin oil

Caesium and rubidium are stored in vacuum-sealed ampoules
40.1 Characteristic Properties of the s-Block Elements (SB p.39) caesium rubidium Caesium and rubidium are stored in vacuum-sealed ampoules

40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character All Group I elements  body-centred cubic structures  much empty space  comparatively low densities

Some information about Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.39) Some information about Group I elements Group I element Atomic radius (nm) Ionic radius (nm) Metallic structure Melting point (C) Lithium Sodium Potassium Rubidium Caesium Francium 0.152 0.186 0.231 0.244 0.262 0.270 0.060 0.095 0.133 0.148 0.169 0.176 b – 180.5 97.8 63.7 39.1 28.4 27

Some information about Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.39) Some information about Group I elements Group I element Boiling point (C) Density at 20 C (g cm–3) Abundance on Earth (%) Lithium Sodium Potassium Rubidium Caesium Francium 1 330 890 774 688 690 680 0.53 0.97 0.86 1.53 1.87 – 2.36 2.09 Trace

Metallic Character All Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character All Group II elements  greyish solids at room temperature and pressure  also be cut with a knife, but harder than the alkali metals

40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character All Group II elements  two valence electrons per atom  smaller atomic sizes  metallic bonds are stronger

40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character All Group II elements  the melting points and boiling points are higher than those of Group I elements  show different metallic structures

Metallic Character Beryllium and magnesium
40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character Beryllium and magnesium  hexagonal close-packed structures

Metallic Character Calcium and strontium
40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character Calcium and strontium  face-centred cubic structures

Metallic Character Barium  body-centred cubic structure
40.1 Characteristic Properties of the s-Block Elements (SB p.39) Metallic Character Barium  body-centred cubic structure

Some information about Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.40) Some information about Group II elements Group II element Atomic radius (nm) Ionic radius (nm) Metallic structure Melting point (C) Beryllium Magnesium Calcium Strontium Barium Radium 0.112 0.160 0.197 0.215 0.217 0.220 0.031 0.065 0.099 0.113 0.135 0.140 h f b – 1 278 648.8 839 769 729 697

Some information about Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.40) Some information about Group II elements Group II element Boiling point (C) Density at 20 C (g cm–3) Abundance on Earth (%) Beryllium Magnesium Calcium Strontium Barium Radium 2 477 1 100 1 480 1 380 1 640 1 140 1.85 1.75 1.55 2.54 3.60 5.0 2.33 4.15 0.038 0.042 Trace

Low Electronegativity
40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity All s-block elements  low electronegativity values

40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity All s-block elements  electropositive elements  their atoms have a relatively high tendency to lose their outermost shell electrons

40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity The outermost shell electrons  effectively shielded from the nucleus by the fully-filled inner electron shells  the outermost shell electrons are only loosely held by the nucleus

40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity Going down both Groups I and II  the elements become more electropositive  the atoms tend to lose electrons more readily  the outermost shell electrons are much further away from the nucleus

40.1 Characteristic Properties of the s-Block Elements (SB p.40) Low Electronegativity Group II elements  more electronegative than the Group I elements  the increase in effective nuclear charge  the attractive force between the nucleus and the outermost shell electrons becomes stronger Let's Think 1

Electronegativity values of Groups I and II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.40) Electronegativity values of Groups I and II elements Group I element Electronegativity value Group II element Li Na K Rb Cs Fr 1.0 0.9 0.8 0.7 – Be Mg Ca Sr Ba Ra 1.5 1.2

Formation of Basic Oxides
40.1 Characteristic Properties of the s-Block Elements (SB p.41) Formation of Basic Oxides 1. Group I Elements All alkali metals form more than one type of oxide on burning in air (except lithium)

1. Group I Elements Three types of oxides:  normal oxides  peroxides
40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements Three types of oxides:  normal oxides  peroxides  superoxides

1. Group I Elements They are all ionic They can be related as follows:
40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements They are all ionic They can be related as follows: O2– oxide ion O22–peroxide ion 2O2–superoxide ion

1. Group I Elements Lithium
40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements Lithium  when it is burnt in air, it forms normal oxide only 4Li(s) + O2(g) Li2O(s) lithium oxide

1. Group I Elements Sodium
40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements Sodium  when it is burnt in an abundant supply of oxygen  forms both the normal oxide and the peroxide 4Na(s) + O2(g) Na2O(s) sodium oxide 4Na2O(s) + O2(g) Na2O2(s) sodium peroxide

1. Group I Elements Potassium, rubidium and caesium
40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements Potassium, rubidium and caesium  form the normal oxide, the peroxide and superoxides when they are burnt in air

1. Group I Elements Potassium:
40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements Potassium: 4K(s) + O2(g)  2K2O(s) potassium oxide 2K2O(s) + O2(g)  2K2O2(s) potassium peroxide K2O2(s) + O2(g)  2KO2(s) potassium superoxide

1. Group I Elements Rubidium: 4Rb(s) + O2(g)  2Rb2O(s)
40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements Rubidium: 4Rb(s) + O2(g)  2Rb2O(s) 2Rb2O(s) + O2(g)  2Rb2O2(s) Rb2O2(s) + O2(g)  2RbO2(s)

1. Group I Elements Caesium: 4Cs(s) + O2(g)  2Cs2O(s)
40.1 Characteristic Properties of the s-Block Elements (SB p.41) 1. Group I Elements Caesium: 4Cs(s) + O2(g)  2Cs2O(s) 2Cs2O(s) + O2(g)  2Cs2O2(s) Cs2O2(s) + O2(g)  2CsO2(s)

Oxides formed by Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.41) Oxides formed by Group I elements Group I element Normal oxide Peroxide Superoxide Li Na K Rb Cs Li2O Na2O K2O Rb2O Cs2O – Na2O2 K2O2 Rb2O2 Cs2O2 KO2 RbO2 CsO2

1. Group I Elements Lithium  does not form the peroxide or superoxide
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 1. Group I Elements Lithium  does not form the peroxide or superoxide  the size of lithium ion is very small  leading to its high polarizing power

40.1 Characteristic Properties of the s-Block Elements (SB p.42)
1. Group I Elements When a peroxide ion or superoxide ion approaches a lithium ion  the electron cloud of the peroxide ion or superoxide ion would be greatly distorted by the lithium ion

1. Group I Elements The electron cloud of the superoxide ion is
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 1. Group I Elements The electron cloud of the superoxide ion is greatly distorted by the small lithium ion

1. Group I Elements The greater the distortion of the electron cloud
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 1. Group I Elements The greater the distortion of the electron cloud  the lower the stability of the compound  lithium peroxide and lithium superoxide do not exist

1. Group I Elements Potassium ion, rubidium ion and caesium ion
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 1. Group I Elements Potassium ion, rubidium ion and caesium ion  larger sizes  relatively low polarizing power

1. Group I Elements The electron cloud of the peroxide ion or superoxide ion  not be seriously distorted by the metallic cations  pack around them with a higher stability  able to form stable peroxides or superoxides

2. Group II Elements Beryllium, magnesium and calcium
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 2. Group II Elements Beryllium, magnesium and calcium  form normal oxides only on burning in air 2Be(s) + O2(g)  2BeO(s) 2Mg(s) + O2(g)  2MgO(s) 2Ca(s) + O2(g)  2CaO(s)

2. Group II Elements Strontium and barium
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 2. Group II Elements Strontium and barium  able to form normal oxides and peroxides of the formula MO2 when the metals are burnt in air

2. Group II Elements Strontium
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 2. Group II Elements Strontium 2Sr(s) + O2(g)  2SrO(s) strontium oxide 2SrO(s) + O2(g) SrO2(s) strontium peroxide

2. Group II Elements Barium 2Ba(s) + O2(g)  2BaO(s) barium oxide
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 2. Group II Elements Barium 2Ba(s) + O2(g)  2BaO(s) barium oxide 2BaO(s) + O2(g) 2BaO2(s) barium peroxide 500C 700C

2. Group II Elements All these oxides are basic in nature (except beryllium oxide which is amphoteric)

Oxides formed by Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.42) Oxides formed by Group II elements Group II element Normal oxide Peroxide Superoxide Be Mg Ca Sr Ba BeO MgO CaO SrO BaO – SrO2 BaO2

2. Group II Elements Beryllium peroxide does not exist
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 2. Group II Elements Beryllium peroxide does not exist  the small size of beryllium ion  high polarizing power of beryllium ion

2. Group II Elements The small beryllium ion
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 2. Group II Elements The small beryllium ion  greatly distorts the electron cloud of the peroxide ion  results in instability of the compound

2. Group II Elements Beryllium ion  smaller in size
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 2. Group II Elements Beryllium ion  smaller in size  higher charge than lithium ion

2. Group II Elements Beryllium ion
40.1 Characteristic Properties of the s-Block Elements (SB p.42) 2. Group II Elements Beryllium ion  distorts the electron cloud of the peroxide ion to a greater extent than lithium ion  beryllium peroxide is very unstable

2. Group II Elements The ionic radii of potassium ion and barium ion
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 2. Group II Elements The ionic radii of potassium ion and barium ion  very similar

2. Group II Elements Potassium
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 2. Group II Elements Potassium  forms stable superoxide on burning in air

2. Group II Elements Barium  does not forms stable superoxide
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 2. Group II Elements Barium  does not forms stable superoxide

2. Group II Elements Barium ion  higher charge than potassium ion
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 2. Group II Elements Barium ion  higher charge than potassium ion  higher polarizing power than potassium ion

2. Group II Elements The electron cloud of the superoxide ion
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 2. Group II Elements The electron cloud of the superoxide ion  greatly distorted by barium ion

2. Group II Elements Barium ion
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 2. Group II Elements Barium ion  difficult to pack with the large superoxide ions in a stable ionic lattice

Formation of Hydroxides
40.1 Characteristic Properties of the s-Block Elements (SB p.43) Formation of Hydroxides 1. Group I Elements All Group I elements (except lithium)  react with water to form metal hydroxides and hydrogen gas

1. Group I Elements 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g)
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 1. Group I Elements 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g) 2K(s) + 2H2O(l)  2KOH(aq) + H2(g) 2Rb(s) + 2H2O(l)  2RbOH(aq) + H2(g) 2Cs(s) + 2H2O(l)  2CsOH(aq) + H2(g)

1. Group I Elements They are basic oxides
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 1. Group I Elements They are basic oxides  react exothermically with water to form the corresponding hydroxides

1. Group I Elements For normal oxides M2O(s) + H2O(l)  2MOH(aq)
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 1. Group I Elements For normal oxides M2O(s) + H2O(l)  2MOH(aq)

1. Group I Elements For peroxides
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 1. Group I Elements For peroxides M2O2(s) + 2H2O(l)  2MOH(aq) + H2O2(aq)

1. Group I Elements For superoxides
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 1. Group I Elements For superoxides 2MO2(s) + 2H2O(l)  2MOH(aq) + H2O2(aq) + O2(g) where M2O, M2O2 and MO2 represent the normal oxides, peroxides and superoxides of Group I elements respectively

1. Group I Elements Hydroxides of the Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.43) 1. Group I Elements Hydroxides of the Group I elements  the strongest bases known (except lithium hydroxide)

2. Group II Elements All Group II elements (except beryllium and magnesium)  react with water to form metal hydroxides and hydrogen gas  less vigorous than the Group I elements in the same period

2. Group II Elements Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g)
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 2. Group II Elements Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g) Sr(s) + 2H2O(l)  Sr(OH)2(aq) + H2(g) Ba(s) + 2H2O(l)  Ba(OH)2(aq) + H2(g)

2. Group II Elements Beryllium  does not react with water or steam
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 2. Group II Elements Beryllium  does not react with water or steam

2. Group II Elements Magnesium  reacts very slowly with water
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 2. Group II Elements Magnesium  reacts very slowly with water  but reacts more quickly with steam to form magnesium oxide and hydrogen gas Mg(s) + H2O(g)  MgO(s) + H2(g)

2. Group II Elements Calcium and strontium
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 2. Group II Elements Calcium and strontium  react readily with water at room temperature and pressure  the reactivity of Group II elements with water increases down the group

2. Group II Elements The hydroxides of calcium, strontium and barium
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 2. Group II Elements The hydroxides of calcium, strontium and barium  prepared by reacting the normal oxides with water CaO(s) + H2O(l)  Ca(OH)2(aq) SrO(s) + H2O(l)  Sr(OH)2(aq) BaO(s) + H2O(l)  Ba(OH)2(aq)

2. Group II Elements Magnesium oxide  only slightly soluble in water
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 2. Group II Elements Magnesium oxide  only slightly soluble in water  but it dissolves in acids to form salts

2. Group II Elements Beryllium oxide
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 2. Group II Elements Beryllium oxide  almost insoluble in water or in acids

Calcium reacts readily with water at room temperature and pressure
40.1 Characteristic Properties of the s-Block Elements (SB p.44) Calcium reacts readily with water at room temperature and pressure

Ionic Bonding with Fixed Oxidation State in their Compounds
40.1 Characteristic Properties of the s-Block Elements (SB p.44) Ionic Bonding with Fixed Oxidation State in their Compounds s-Block elements form compounds  predominantly ionic in nature  show constant oxidation states of +1 for Group I elements and +2 for Group II elements

1. Group I Elements For Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 1. Group I Elements For Group I elements  form ions with an oxidation state of only  their atoms have only one outermost shell electron

1. Group I Elements Once this outermost shell electron is removed
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 1. Group I Elements Once this outermost shell electron is removed  a stable fully-filled electronic configuration is obtained  the first ionization enthalpies of Group I elements are low

1. Group I Elements The second ionization
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 1. Group I Elements The second ionization  involves the removal of an electron from an inner electron shell

1. Group I Elements Once this electron is removed
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 1. Group I Elements Once this electron is removed  the stable electronic configuration will be disrupted  their second ionization enthalpies are very high

1. Group I Elements Group I elements
40.1 Characteristic Properties of the s-Block Elements (SB p.44) 1. Group I Elements Group I elements  form predominantly ionic compounds with non-metals  by losing their single outermost shell electrons  form ions having a fixed oxidation state of +1

Oxidation state of Group I element in the compound
40.1 Characteristic Properties of the s-Block Elements (SB p.45) Chemical formulae of some Group I compounds and the oxidation states of Group I elements in the compounds Group I element Oxide Hydride Chloride Oxidation state of Group I element in the compound Li Na K Rb Cs Li2O Na2O2 KO2 RbO2 CsO2 LiH NaH KH RbH CsH LiCl NaCl KCl RbCl CsCl +1

2. Group II Elements For Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.45) 2. Group II Elements For Group II elements  they form ions with an oxidation state of +2 only  their atoms have two outermost shell electrons in the s orbital

2. Group II Elements Once these two outermost shell electrons are removed  a stable fully-filled electronic configuration is obtained  the sum of the first and second ionization enthalpies of Group II elements is relatively low

2. Group II Elements The third ionization
40.1 Characteristic Properties of the s-Block Elements (SB p.45) 2. Group II Elements The third ionization  corresponds to the removal of an electron from an inner fully-filled electron shell

2. Group II Elements The third ionization enthalpy
40.1 Characteristic Properties of the s-Block Elements (SB p.45) 2. Group II Elements The third ionization enthalpy  an extremely large positive value for these elements  these elements do not form ions with an oxidation state of +3

2. Group II Elements Group II elements
40.1 Characteristic Properties of the s-Block Elements (SB p.45) 2. Group II Elements Group II elements  form predominantly ionic compounds with non-metals  by losing their two outermost shell electrons  form ions having a fixed oxidation state of +2

Oxidation state of Group II element in the compound
40.1 Characteristic Properties of the s-Block Elements (SB p.45) Chemical formulae of some Group II compounds and the oxidation states of Group II elements in the compounds Group II element Oxide Hydride Chloride Oxidation state of Group II element in the compound Be Mg Ca Sr Ba BeO MgO CaO SrO BaO BeH2 MgH2 CaH2 SrH2 BaH2 BeCl2 MgCl2 CaCl2 SrCl2 BaCl2 +2

Characteristic Flame Colours of Salts
40.1 Characteristic Properties of the s-Block Elements (SB p.45) Characteristic Flame Colours of Salts Most s-block elements  give a characteristic flame colour in the flame test

40.1 Characteristic Properties of the s-Block Elements (SB p.45) Characteristic Flame Colours of Salts Method:  putting a sample of the elements or their compounds into a non-luminous Bunsen flame

40.1 Characteristic Properties of the s-Block Elements (SB p.45) Characteristic Flame Colours of Salts The outermost shell electrons of atoms of both Groups I and II elements  weakly held by the nucleus  the electrons are easily excited to higher energy levels upon heating

40.1 Characteristic Properties of the s-Block Elements (SB p.46) Characteristic Flame Colours of Salts When these electrons return to their ground states  radiation is emitted  falls into the visible light region of the electromagnetic spectrum

40.1 Characteristic Properties of the s-Block Elements (SB p.46) Characteristic Flame Colours of Salts The amount of energy of the emitted radiation is quantized  the flame colour is a characteristic property of the element

40.1 Characteristic Properties of the s-Block Elements (SB p.46) Characteristic Flame Colours of Salts Example: Sodium chloride

40.1 Characteristic Properties of the s-Block Elements (SB p.46) Characteristic Flame Colours of Salts When sodium chloride is heated in a Bunsen flame  the ions are converted to gaseous atoms Na+ Cl–(g)  Na(g) + Cl(g)

40.1 Characteristic Properties of the s-Block Elements (SB p.46) Characteristic Flame Colours of Salts The electrons in the gaseous sodium atoms  excited to higher energy levels

40.1 Characteristic Properties of the s-Block Elements (SB p.46) Characteristic Flame Colours of Salts When the excited electrons return to their ground state  light of golden yellow colour is given out  gives a golden yellow flame on burning

The characteristic flame colours of some Groups I and II elements in the flame test Group I element Flame colour Group II element Li Na K Rb Cs Deep reed Golden yellow Lilac Bluish red Blue Ca Sr Ba Brick-red Blood-red or crimson Green Let's Think 2

(d) Characteristic flame colours of some Groups I and II elements in the flame test: (a) lithium-containing compounds give a deep red flame; (b) sodium-containing compounds give a golden yellow flame; (c) potassium-containing compounds give a lilac flame; (d) calcium containing compounds give a brick-red flame

Weak Tendency to Form Complexes
40.1 Characteristic Properties of the s-Block Elements (SB p.48) Weak Tendency to Form Complexes A complex is formed when a central metal atom or ion is surrounded by other molecules or ions (called ligands) which form dative covalent bonds with the central metal atom or ion.

40.1 Characteristic Properties of the s-Block Elements (SB p.48) Weak Tendency to Form Complexes Complex formation  a common characteristic of d-block metal ions

40.1 Characteristic Properties of the s-Block Elements (SB p.48) Weak Tendency to Form Complexes When a d-block metal ion is surrounded by ligands (such as NH3 and Cl–)  the lone pair electrons of the ligands can be donated to the central d-block metal ion  form dative covalent bonds Let's Think 3

40.1 Characteristic Properties of the s-Block Elements (SB p.48) Weak Tendency to Form Complexes Example:

40.1 Characteristic Properties of the s-Block Elements (SB p.48) Weak Tendency to Form Complexes The presence of low-lying vacant d-orbitals in the d-block metal ions  accept the lone pair electrons from the surrounding ligands

40.1 Characteristic Properties of the s-Block Elements (SB p.48) Weak Tendency to Form Complexes s-Block metal ions  also be surrounded by polar molecules  but there is only electrostatic attraction between the metal ion and the negative ends of the dipoles

40.1 Characteristic Properties of the s-Block Elements (SB p.48) Weak Tendency to Form Complexes s-Block metal ions  do not have low-lying vacant orbitals available for forming dative covalent bonds  rarely form complexes Check Point 40-1

The atomic radii and ionic radii of most Groups I elements
40.2 Variation in Properties of the s-Block Elements (SB p.49) Variation in Physical Properties 1. Atomic Radius and Ionic Radius The atomic radii and ionic radii of most Groups I elements Group I element Atomic radius (nm) Ionic radius (nm) Li Na K Rb Cs 0.152 0.186 0.231 0.244 0.262 0.060 0.095 0.133 0.148 0.169

The atomic radii and ionic radii of most Groups II elements
40.2 Variation in Properties of the s-Block Elements (SB p.49) The atomic radii and ionic radii of most Groups II elements Group II element Atomic radius (nm) Ionic radius (nm) Be Mg Ca Sr Ba 0.112 0.160 0.197 0.215 0.217 0.031 0.065 0.099 0.113 0.135

40.2 Variation in Properties of the s-Block Elements (SB p.49)
Variations in atomic radius and ionic radius of Groups I and II elements

Atoms of all Groups I and II elements
40.2 Variation in Properties of the s-Block Elements (SB p.50) 1. The ionic radius of any Groups I or II element is smaller than its atomic radius Atoms of all Groups I and II elements  form their respective M+ and M2+ ions by losing their outermost s electrons

There is one electron shell less in the cation than the atom
40.2 Variation in Properties of the s-Block Elements (SB p.50) 1. The ionic radius of any Groups I or II element is smaller than its atomic radius There is one electron shell less in the cation than the atom  the nucleus pulls the electron cloud more closely towards it  the ionic radius is smaller than the atomic radius

 more electron shells occupied
40.2 Variation in Properties of the s-Block Elements (SB p.50) 2. Going down both Groups I and II, both the atomic radii and ionic radii increase The atoms or the ions  more electron shells occupied  the outermost electron shells become further away from the nucleus

The outermost shell electrons
40.2 Variation in Properties of the s-Block Elements (SB p.50) 2. Going down both Groups I and II, both the atomic radii and ionic radii increase The outermost shell electrons  more effectively shielded by the inner shell electrons from the nuclear charge

 both the atomic radii and ionic radii increase down a group
40.2 Variation in Properties of the s-Block Elements (SB p.50) 2. Going down both Groups I and II, both the atomic radii and ionic radii increase A decrease in the attractive force between the nucleus and the outermost shell electrons  both the atomic radii and ionic radii increase down a group

Each atom of the Group II element
40.2 Variation in Properties of the s-Block Elements (SB p.50) 3. Going from Group I to Group II in each period, the atomic radii and ionic radii decrease Each atom of the Group II element  one more electron in the outermost shell  one more proton in the nucleus than each atom of the Group I element in the same period

The additional electron  enters the same shell
40.2 Variation in Properties of the s-Block Elements (SB p.50) 3. Going from Group I to Group II in each period, the atomic radii and ionic radii decrease The additional electron  enters the same shell  at approximately the same distance from the nucleus

The repulsion between electrons
40.2 Variation in Properties of the s-Block Elements (SB p.50) 3. Going from Group I to Group II in each period, the atomic radii and ionic radii decrease The repulsion between electrons  relatively ineffective to cause an increase in both the atomic radius and ionic radius

3. Going from Group I to Group II in each period, the atomic radii and ionic radii decrease There is only very little or even no increase in the shielding (or screening) effect of the inner shell electrons on the outermost shell electrons

The additional proton in the nucleus of the atoms of Group II elements
40.2 Variation in Properties of the s-Block Elements (SB p.50) 3. Going from Group I to Group II in each period, the atomic radii and ionic radii decrease The additional proton in the nucleus of the atoms of Group II elements  stronger attractive force to the electrons  the atomic radii and ionic radii of the Group II elements are smaller

Ionization enthalpies of Groups I elements
40.2 Variation in Properties of the s-Block Elements (SB p.50) 2. Ionization Enthalpy Ionization enthalpies of Groups I elements Group I element First ionization enthalpy (kJ mol–1) Second ionization enthalpy (kJ mol–1) Li Na K Rb Cs Fr 519 494 418 402 376 381 7 300 4 560 3 070 2 370 2 420 –

Ionization enthalpies of Groups II elements
40.2 Variation in Properties of the s-Block Elements (SB p.50) Ionization enthalpies of Groups II elements Group II element First ionization enthalpy (kJ mol–1) Second ionization enthalpy (kJ mol–1) Third ionization enthalpy (kJ mol–1) Be Mg Ca Sr Ba Ra 900 736 590 548 502 510 1 760 1 450 1 150 1 060 966 979 14 800 7 740 4 940 4 120 3 390 –

Variations in the first and second ionization enthalpies of Group I elements

Variations in the first, second and third ionization enthalpies of Group II elements

The outermost s electron  located in a new electron shell
40.2 Variation in Properties of the s-Block Elements (SB p.52) 1. The first ionization enthalpies of Group I elements are relatively low The outermost s electron  located in a new electron shell

The attractive force between this s electron and the nucleus
40.2 Variation in Properties of the s-Block Elements (SB p.52) 1. The first ionization enthalpies of Group I elements are relatively low The attractive force between this s electron and the nucleus  relatively weak

The outermost s electron
40.2 Variation in Properties of the s-Block Elements (SB p.52) 1. The first ionization enthalpies of Group I elements are relatively low The outermost s electron  effectively shielded from the attraction of the nucleus by the fully- filled inner electron shells

Once this electron is removed
40.2 Variation in Properties of the s-Block Elements (SB p.52) 1. The first ionization enthalpies of Group I elements are relatively low Once this electron is removed  a stable octet or duplet electronic configuration is attained

The outermost s electron  relatively easy to be removed
40.2 Variation in Properties of the s-Block Elements (SB p.52) 1. The first ionization enthalpies of Group I elements are relatively low The outermost s electron  relatively easy to be removed  the first ionization enthalpies for Group I elements are relatively low

The second ionization of Group I elements
40.2 Variation in Properties of the s-Block Elements (SB p.52) 1. The first ionization enthalpies of Group I elements are relatively low The second ionization of Group I elements  involves the loss of an inner shell electron  closer to the nucleus

The removal of this electron
40.2 Variation in Properties of the s-Block Elements (SB p.52) 1. The first ionization enthalpies of Group I elements are relatively low The removal of this electron  disrupts the stable electronic configuration  the second ionization enthalpies of Group I elements are extremely high

The two outermost s electrons of atoms of Group II elements
40.2 Variation in Properties of the s-Block Elements (SB p.52) 2. The first and second ionization enthalpies of Group II elements are relatively low The two outermost s electrons of atoms of Group II elements  relatively easy to be removed  these two electrons are effectively shielded from the nucleus by inner electron shells

Once these two electrons are removed
40.2 Variation in Properties of the s-Block Elements (SB p.52) 2. The first and second ionization enthalpies of Group II elements are relatively low Once these two electrons are removed  a stable octet or duplet electronic configuration is attained

The third ionization of Group II elements
40.2 Variation in Properties of the s-Block Elements (SB p.52) 2. The first and second ionization enthalpies of Group II elements are relatively low The third ionization of Group II elements  involves the loss of an inner shell electron  closer to the nucleus

The stable electronic configuration
40.2 Variation in Properties of the s-Block Elements (SB p.52) 2. The first and second ionization enthalpies of Group II elements are relatively low The stable electronic configuration  disrupte after the removal of this electron  the third ionization enthalpies of Group II elements are very high

There is an increase in atomic radius down the groups
40.2 Variation in Properties of the s-Block Elements (SB p.52) 3. Going down both Groups I and II, the ionization enthalpy generally decreases There is an increase in atomic radius down the groups

The outermost shell electrons of the atoms  far away from the nucleus
40.2 Variation in Properties of the s-Block Elements (SB p.52) 3. Going down both Groups I and II, the ionization enthalpy generally decreases The outermost shell electrons of the atoms  far away from the nucleus  experience less attraction from the positively charged nucleus  less energy is required to remove the outermost shell electrons of the atoms

3. Hydration enthalpy Hydration enthalpy (Hhyd) is the amount of energy released when one mole of aqueous ions is formed from its gaseous ions.

3. Hydration enthalpy M+(g) + aq  M+(aq) H = Hhyd
40.2 Variation in Properties of the s-Block Elements (SB p.52) 3. Hydration enthalpy M+(g) + aq  M+(aq) H = Hhyd  always has a negative value

3. Hydration enthalpy M+(g) + aq  M+(aq) H = Hhyd
40.2 Variation in Properties of the s-Block Elements (SB p.52) 3. Hydration enthalpy M+(g) + aq  M+(aq) H = Hhyd  the amount of energy released resulting from the attraction between ions and water molecules  depends on the charge to radius ratio of the ion

3. Hydration enthalpy The greater the charge on the ion
40.2 Variation in Properties of the s-Block Elements (SB p.52) 3. Hydration enthalpy The greater the charge on the ion  the stronger the attraction between the ion and the water molecules  the larger the amount of energy given out

3. Hydration enthalpy The smaller the size of the ion
40.2 Variation in Properties of the s-Block Elements (SB p.52) 3. Hydration enthalpy The smaller the size of the ion  the higher the effective nuclear charge  the stronger the attraction between the ion and the water molecules  a large amount of energy is released

Hydration enthalpies of the ions of Groups I and II elements
40.2 Variation in Properties of the s-Block Elements (SB p.53) Hydration enthalpies of the ions of Groups I and II elements Group I ion Hydration enthalpy (kJ mol–1) Group II ion Li+ Na+ K+ Rb+ Cs+ Fr+ –519 –406 –322 –301 –276 – Be 2+ Mg2+ Ca2+ Sr2+ Ba2+ Ra2+ –2 450 –1 920 –1 650 –1 480 –1 360

Variations in hydration enthalpy of the ions of
40.2 Variation in Properties of the s-Block Elements (SB p.53) Variations in hydration enthalpy of the ions of Groups I and II elements

 larger in size down both groups
40.2 Variation in Properties of the s-Block Elements (SB p.54) 1. Going down both Groups I and II, the hydration enthalpy of the ions decreases (becomes less negative) The ions  larger in size down both groups  the charge density of the ions falls

The electrostatic attraction between the ions and water molecules
40.2 Variation in Properties of the s-Block Elements (SB p.54) 1. Going down both Groups I and II, the hydration enthalpy of the ions decreases (becomes less negative) The electrostatic attraction between the ions and water molecules  weaker

The hydration enthalpy  less negative on going down the groups
40.2 Variation in Properties of the s-Block Elements (SB p.54) 1. Going down both Groups I and II, the hydration enthalpy of the ions decreases (becomes less negative) The hydration enthalpy  less negative on going down the groups

 a smaller ionic radius
40.2 Variation in Properties of the s-Block Elements (SB p.54) 2. The ions of Group II elements have more negative hydration enthalpies than those of Group I elements in the same period Group II ions  a charge of +2  a smaller ionic radius  higher charge density than the Group I ions in the same period

 stronger than that between the Group I ions and water molecules
40.2 Variation in Properties of the s-Block Elements (SB p.54) 2. The ions of Group II elements have more negative hydration enthalpies than those of Group I elements in the same period The electrostatic attraction between the Group II ions and water molecules  stronger than that between the Group I ions and water molecules

4. Melting Point The melting points of Groups I and II elements depend on  the strength of the metallic bonding  how the atoms are arranged in the metallic crystal lattice

4. Melting Point The stronger the metallic bond
40.2 Variation in Properties of the s-Block Elements (SB p.54) 4. Melting Point The stronger the metallic bond  the higher the melting point of the element

4. Melting Point The strength of metallic bond depends on:
40.2 Variation in Properties of the s-Block Elements (SB p.54) 4. Melting Point The strength of metallic bond depends on: 1. the ionic radius of the metal ion; 2. the number of valence electrons per atom of the element

The melting points of Groups I and II elements
40.2 Variation in Properties of the s-Block Elements (SB p.54) The melting points of Groups I and II elements Group I element Melting Point (C) Group II element Li Na K Rb Cs Fr 180 97.8 63.7 38.9 28.7 24 Be Mg Ca Sr Ba Ra 1280 650 850 768 714 697

Variations in melting point of Groups I and II elements
40.2 Variation in Properties of the s-Block Elements (SB p.55) Variations in melting point of Groups I and II elements

 the ionic radii of the metal ions increase
40.2 Variation in Properties of the s-Block Elements (SB p.55) 1. Going down both Groups I and II, the melting points generally decrease In each group  the number of electrons participating in metallic bonding remains the same  the ionic radii of the metal ions increase

The attractive forces between the electron sea and the metal ions
40.2 Variation in Properties of the s-Block Elements (SB p.55) 1. Going down both Groups I and II, the melting points generally decrease The attractive forces between the electron sea and the metal ions  weaker  the metallic bond becomes weaker going down the groups

The ions of Group I elements  carry one positive charge only
40.2 Variation in Properties of the s-Block Elements (SB p.55) 2. The melting points of Group II elements are much higher than those of Group I elements The ions of Group I elements  carry one positive charge only The ions of Group II elements  carry two positive charges

 the greater number of valence electrons
40.2 Variation in Properties of the s-Block Elements (SB p.55) 2. The melting points of Group II elements are much higher than those of Group I elements The Group II elements  the greater number of valence electrons  the smaller ionic radii

The attractive forces between the metal ions and the electron sea
40.2 Variation in Properties of the s-Block Elements (SB p.55) 2. The melting points of Group II elements are much higher than those of Group I elements The attractive forces between the metal ions and the electron sea  stronger in Group II elements

 stronger in Group II elements
40.2 Variation in Properties of the s-Block Elements (SB p.55) 2. The melting points of Group II elements are much higher than those of Group I elements The metallic bond  stronger in Group II elements

Melting point of a metal depends on
40.2 Variation in Properties of the s-Block Elements (SB p.55) 3. The general decrease in melting point down Group II elements is broken with an irregularity ― the melting point of magnesium is lower than that of calcium Melting point of a metal depends on  how the individual atoms are packed in the crystal lattice

3. The general decrease in melting point down Group II elements is broken with an irregularity ― the melting point of magnesium is lower than that of calcium Magnesium atoms  not particularly well packed in the crystal lattice as compared to calcium atoms Check Point 40-2A

Variation in Chemical Properties
40.2 Variation in Properties of the s-Block Elements (SB p.56) Variation in Chemical Properties s-Block elements have strong reducing power  reflected by their low ionization enthalpies

40.2 Variation in Properties of the s-Block Elements (SB p.56) Variation in Chemical Properties The lower the ionization enthalpy  the stronger the reducing power of the metal

40.2 Variation in Properties of the s-Block Elements (SB p.56) Variation in Chemical Properties Going down both Groups I and II  the atomic size increases  easier for the atoms to lose the outermost shell electrons  the ionization enthalpy decreases accordingly  the reducing power of the metals increases down the groups

40.2 Variation in Properties of the s-Block Elements (SB p.56) Variation in Chemical Properties Group I metals  react readily with oxygen and water by losing their single outermost shell electron

40.2 Variation in Properties of the s-Block Elements (SB p.56) Variation in Chemical Properties Group II metals  generally less reactive than Group I metals  their higher ionization enthalpies

1. Reaction with Oxygen Most s-block elements
40.2 Variation in Properties of the s-Block Elements (SB p.56) 1. Reaction with Oxygen Most s-block elements  show a silvery white lustre when they are freshly cut  they tarnish rapidly upon exposure to the atmosphere  they react with oxygen in the air to form an oxide layer

Sodium shows a silvery white lustre when freshly cut
40.2 Variation in Properties of the s-Block Elements (SB p.56) Sodium shows a silvery white lustre when freshly cut

1. Reaction with Oxygen s-block elements (except beryllium and magnesium)  very reactive  stored under paraffin oil or in vacuum-sealed ampoules  prevent contact with oxygen and water vapour in the air

1. Reaction with Oxygen Beryllium and magnesium
40.2 Variation in Properties of the s-Block Elements (SB p.56) 1. Reaction with Oxygen Beryllium and magnesium  form an oxide layer with oxygen  but they tarnish comparatively slowly

1. Reaction with Oxygen All s-block elements
40.2 Variation in Properties of the s-Block Elements (SB p.56) 1. Reaction with Oxygen All s-block elements  burn in air to form one or more of the three types of oxides

1. Reaction with Oxygen Three types of oxides  normal oxides
40.2 Variation in Properties of the s-Block Elements (SB p.56) 1. Reaction with Oxygen Three types of oxides  normal oxides  peroxides  superoxides

“Dot-and-cross” diagrams of the three types of oxide ions
40.2 Variation in Properties of the s-Block Elements (SB p.56) “Dot-and-cross” diagrams of the three types of oxide ions

1. Reaction with Oxygen On burning in air, lithium
40.2 Variation in Properties of the s-Block Elements (SB p.57) 1. Reaction with Oxygen On burning in air, lithium  forms only lithium oxide (Li2O)

1. Reaction with Oxygen On burning in air, sodium
40.2 Variation in Properties of the s-Block Elements (SB p.57) 1. Reaction with Oxygen On burning in air, sodium  forms a mixture of sodium monoxide (Na2O) and sodium peroxide (Na2O2)

1. Reaction with Oxygen On burning in air, potassium, rubidium and caesium  form the normal oxides, peroxides and superoxides

1. Reaction with Oxygen Example: 4K(s) + O2(g) 2K2O(s) potassium oxide
40.2 Variation in Properties of the s-Block Elements (SB p.57) 1. Reaction with Oxygen Example: 4K(s) + O2(g) 2K2O(s) potassium oxide 2K2O(s) + O2(g) K2O2(s) potassium peroxide K2O2(s) + O2(g) KO2(s) potassium superoxide

1. Reaction with Oxygen Group II elements
40.2 Variation in Properties of the s-Block Elements (SB p.57) 1. Reaction with Oxygen Group II elements  form the normal oxides when they are burnt in air 2Be(s) + O2(g)  2BeO(s) 2Mg(s) + O2(g)  2MgO(s)

1. Reaction with Oxygen Beryllium and magnesium
40.2 Variation in Properties of the s-Block Elements (SB p.57) 1. Reaction with Oxygen Beryllium and magnesium  relatively unreactive towards oxygen at room temperature and pressure  burn with a brilliant white flame when ignited

Magnesium burns vigorously in air
40.2 Variation in Properties of the s-Block Elements (SB p.57) Magnesium Magnesium burns vigorously in air

Magnesium oxide is formed after burning
40.2 Variation in Properties of the s-Block Elements (SB p.57) Magnesium oxide Magnesium oxide is formed after burning

1. Reaction with Oxygen Strontium and barium
40.2 Variation in Properties of the s-Block Elements (SB p.57) 1. Reaction with Oxygen Strontium and barium  form the normal oxides and peroxides on burning in air 2Ba(s) + O2(g)  2BaO(s) barium oxide 2BaO(s) + O2(g) 2BaO2(s) barium peroxide 500C 700C

1. Reaction with Oxygen Strontium and barium
40.2 Variation in Properties of the s-Block Elements (SB p.57) 1. Reaction with Oxygen Strontium and barium  very reactive at room temperature and pressure  stored under paraffin oil to prevent contact with air

Oxides formed by the s-block elements
40.2 Variation in Properties of the s-Block Elements (SB p.57) Oxides formed by the s-block elements Type of oxide Formula Metals that form oxides when exposed to air or burnt in air Normal oxide O2– All Groups I and II elements Peroxide O22– Na, K, Rb, Cs, Sr, Ba Superoxide K, Rb, Cs Let's Think 4

2. Reaction with Water All Group I metals
40.2 Variation in Properties of the s-Block Elements (SB p.57) 2. Reaction with Water All Group I metals  react with cold water to form metal hydroxides and hydrogen

2. Reaction with Water Example:
40.2 Variation in Properties of the s-Block Elements (SB p.57) 2. Reaction with Water Example: 2Li(s) + 2H2O(l)  2LiOH(aq) + H2(g) (vigorous) 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g) (violent) 2K(s) + 2H2O(l)  2KOH(aq) + H2(g) (explosive)

2. Reaction with Water All Group I metals
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water All Group I metals  reduce cold water to form hydroxide ions and hydrogen H2O(l) + e–  OH–(aq) + H2(g)

2. Reaction with Water The reactivity of Group I metals with water
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water The reactivity of Group I metals with water  related to the relative ease of the metal atoms to lose the outermost shell electron

2. Reaction with Water Going down the group
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Going down the group  the atomic size increases  the outermost shell electron becomes easier to be removed  the reactivity of Group I metals towards water increases down the group

2. Reaction with Water Lithium  reacts with water vigorously
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Lithium  reacts with water vigorously

2. Reaction with Water Sodium  reacts with water violently
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Sodium  reacts with water violently  moves on the water surface with a hissing sound

2. Reaction with Water Potassium  reacts with water explosively
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Potassium  reacts with water explosively  producing a lilac flame

2. Reaction with Water Rubidium and caesium
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Rubidium and caesium  react with water explosively

Lithium reacts with water vigorously
40.2 Variation in Properties of the s-Block Elements (SB p.58) Lithium reacts with water vigorously

Sodium reacts with water violently
40.2 Variation in Properties of the s-Block Elements (SB p.58) Sodium reacts with water violently

Potassium reacts with water explosively
40.2 Variation in Properties of the s-Block Elements (SB p.58) Potassium reacts with water explosively

2. Reaction with Water For Group II metals
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water For Group II metals  less reactive than the Group I metals in the same period

2. Reaction with Water Beryllium  does not react with water
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Beryllium  does not react with water

2. Reaction with Water Magnesium
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Magnesium  reacts with steam rapidly to form magnesium oxide and hydrogen gas Mg(s) + H2O(g)  MgO(s) + H2(g) (vigorous)

2. Reaction with Water Magnesium
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Magnesium  reacts with cold water very slowly to form magnesium hydroxide and hydrogen gas Mg(s) + 2H2O(l)  Mg(OH)2(aq) + H2(g) (very slow)

2. Reaction with Water Calcium  reacts with water steadily
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Calcium  reacts with water steadily Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g) (moderate)

2. Reaction with Water Strontium and barium
40.2 Variation in Properties of the s-Block Elements (SB p.58) 2. Reaction with Water Strontium and barium  react with water vigorously Sr(s) + 2H2O(l)  Sr(OH)2(aq) + H2(g) (vigorous) Check Point 40-2B

Reactions of Oxides of s-Block Elements
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) Reactions of Oxides of s-Block Elements 1. Reaction with Water The oxides of all Group I elements  react with water to form the corresponding hydroxides  it is exothermic

1. Reaction with Water For the normal oxides of Group I elements
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water For the normal oxides of Group I elements  react with water to form metal hydroxides  as the only products Li2O(s) + H2O(l)  2LiOH(aq)

40. 3 Variation in Properties of the Compounds of the s-Block Elements
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water For peroxides and superoxides of Group I elements  other products are formed

1. Reaction with Water For peroxides of Group I elements
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water For peroxides of Group I elements  react with water to form metal hydroxides and hydrogen peroxide Na2O2(s) + 2H2O(l)  2NaOH(aq) + H2O2(aq)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) Dissolution of sodium peroxide in water containing phenolphthalein (The red colour is due to the formation of hydroxide ions which turn phenolphthalein from colourless to red)

1. Reaction with Water For the superoxides of Group I elements
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water For the superoxides of Group I elements  react with water to form metal hydroxides, hydrogen peroxide and oxygen 2KO2(s) + 2H2O(l)  2KOH(aq) + H2O2(aq) + O2(g)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water The basicity of the oxides of Group I elements increases down the group

1. Reaction with Water The oxides of Group II elements
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water The oxides of Group II elements  generally less basic than those of Group I elements

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water The oxides of all Group II elements (except beryllium oxide and magnesium oxide)  react with water to form weakly alkaline solutions

1. Reaction with Water Example:
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water Example: CaO(s) + H2O(l)  Ca(OH)2(aq) (weakly alkaline) SrO(s) + H2O(l)  Sr(OH)2(aq) (weakly alkaline)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water The basicity of the oxides of Group II elements also increases down the group

1. Reaction with Water Beryllium oxide  amphoteric
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water Beryllium oxide  amphoteric  almost insoluble in water or in acids  its amphoteric nature is shown only in its reactions with hot acids or alkalis

1. Reaction with Water BeO(s) + 2H+(aq) hot  Be2+(aq) + H2O(l)
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water BeO(s) + 2H+(aq) hot  Be2+(aq) + H2O(l) BeO(s) + 2OH–(aq) + H2O(l) hot  [Be(OH)4]2–(aq) beryllate ion

1. Reaction with Water Magnesium oxide
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water Magnesium oxide  only slightly soluble in water  dissolves in acids to form salts

1. Reaction with Water The oxides of other Group II elements
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.59) 1. Reaction with Water The oxides of other Group II elements  soluble in water  solubility increases down the group

1. Reaction with Water Barium peroxide
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 1. Reaction with Water Barium peroxide  reacts readily with cold water to form barium hydroxide and hydrogen peroxide BaO2(s) + 2H2O(l)  Ba(OH)2(aq) + H2O2(aq)

1. Reaction with Water Metal peroxides and metal superoxides
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 1. Reaction with Water Metal peroxides and metal superoxides  strong oxidizing agents  indicated by their reactions with water to give hydrogen peroxide

1. Reaction with Water Sodium peroxide
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 1. Reaction with Water Sodium peroxide  oxidizes green chromium(III) hydroxide to yellow sodium chromate(VI)

1. Reaction with Water Metal peroxides and metal superoxides
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 1. Reaction with Water Metal peroxides and metal superoxides  useful in both qualitative and quantitative analysis 2Cr(OH)3(s) + 3Na2O2(s)  2Na2CrO4(aq) NaOH(aq) + 2H2O(l)

2. Reaction with Dilute Acids
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 2. Reaction with Dilute Acids All oxides of Groups I and II elements (Except beryllium oxide is amphoteric)  basic  react readily with dilute acids

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 2. Reaction with Dilute Acids Their normal oxides  neutralize the acids to form salts and water CaO(s) + 2HCl(aq)  CaCl2(aq) + H2O(l)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 2. Reaction with Dilute Acids Their peroxides  react with dilute acids to form salts and hydrogen peroxide Na2O2(s) + 2HCl(aq)  2NaCl(aq) + H2O2(aq)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 2. Reaction with Dilute Acids Their superoxides  react with dilute acids to form salts, hydrogen peroxide and oxygen 2KO2(s) + 2HCl(aq)  2KCl(aq) + H2O2(aq) + O2(g)

3. Reaction with Dilute Alkalis
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 3. Reaction with Dilute Alkalis In general, the oxides of s-block elements do not react with dilute alkalis

3. Reaction with Dilute Alkalis
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) 3. Reaction with Dilute Alkalis Except beryllium oxide  amphoteric  reacts with sodium hydroxide to form sodium beryllate BeO(s) + 2NaOH(aq) + H2O(l)  Na2Be(OH)4(aq)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements Thermal stability refers to the resistance of a compound to undergo decomposition on heating.

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements The higher the thermal stability of a compound  the higher the temperature needed for the compound to decompose thermally

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.60) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements A compound is often said to be thermally stable  not decomposed at the temperature of the normal Bunsen flame (approximately 1300 K)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements The thermal stability of an ionic compound depends on  the charges of its constituent ions  the sizes of its constituent ions

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements For compounds with relatively large polarizable anions  the thermal stability is affected by the polarizing power of the cations

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements If the cation has strong polarizing power  distort the electron clouds of the neighbouring anions to a greater extent

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements The compound  less stable  more likely to decompose on heating

The large anion is polarized by the small cation
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) The large anion is polarized by the small cation

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements Most carbonates and hydroxides of Groups I and II metals  undergo decomposition on heating to give oxides

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements Example: MgCO3(s) MgO(s) + CO2(g) Ca(OH)2(s) CaO(s) + H2O(g)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements Oxide ions  smaller in size than carbonate ions and hydroxide ions  less polarizable

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements The electrostatic attraction between the cations and oxide ions  stronger

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements The oxides of Groups I and II metals  more stable than the corresponding carbonates and hydroxides  decompose to give oxides upon heating

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) When a compound with large anions undergoes thermal decomposition, a compound with small anions will be formed since small anions are less easily polarized

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements Group II metal ions  smaller in size  higher charge  stronger polarizing power

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.61) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements The large carbonate ions and hydroxide ions  distort to a greater extent  more readily to undergo thermal decomposition

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) Effect of sizes of the cations on thermal stability of the carbonates and hydroxides of both Groups I and II metals

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) Relative Thermal Stability of the Carbonates and Hydroxides of s-Block Elements Going down each group  the size of the cations increases  the polarizing power of the cations decreases  the thermal stability increases

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) 1. The Carbonates The carbonates of all Group I metals (except lithium carbonate)  withstand up to a temperature around 800C

1. The Carbonates Lithium carbonate  decomposes at around 700C
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) 1. The Carbonates Lithium carbonate  decomposes at around 700C  form lithium oxide and carbon dioxide Li2CO3(s) Li2O(s) + CO2(g)

1. The Carbonates Lithium carbonate  relatively unstable
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) 1. The Carbonates Lithium carbonate  relatively unstable  lithium ion has the smallest size  the polarizing power is the highest

1. The Carbonates The electron cloud of any large anion
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) 1. The Carbonates The electron cloud of any large anion  distort to a great extent  decompose more readily on heating

1. The Carbonates Group II metal ions  higher charges  smaller sizes
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) 1. The Carbonates Group II metal ions  higher charges  smaller sizes  higher polarizing power

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) 1. The Carbonates The electron cloud of the carbonate ion is much distorted  more readily to undergo thermal decomposition

1. The Carbonates Example: BeCO3(s) BeO(s) + CO2(g)
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.62) 1. The Carbonates Example: BeCO3(s) BeO(s) + CO2(g) MgCO3(s) MgO(s) + CO2(g) CaCO3(s) CaO(s) + CO2(g) SrCO3(s) SrO(s) + CO2(g) BaCO3(s) BaO(s) + CO2(g)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 2. The Hydroxides The hydroxides of all Group I metals (Except lithium hydroxide)  stable to heating with a Bunsen flame

2. The Hydroxides Lithium hydroxide  the least stable on heating
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 2. The Hydroxides Lithium hydroxide  the least stable on heating

2. The Hydroxides Lithium ion  extremely small
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 2. The Hydroxides Lithium ion  extremely small  high polarizing power  distorts the electron cloud of the hydroxide ion  decomposition occurs 2LiOH(s) Li2O(s) + H2O(g)

2. The Hydroxides The hydroxides of Group II metals
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 2. The Hydroxides The hydroxides of Group II metals  less stable to heat  greater the polarizing power

2. The Hydroxides Going down the group  cationic sizes increases
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 2. The Hydroxides Going down the group  cationic sizes increases  thermal stability increases

2. The Hydroxides The enthalpy changes
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 2. The Hydroxides The enthalpy changes  provide evidence for the trend of increasing thermal stability

2. The Hydroxides Example:
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 2. The Hydroxides Example: Be(OH)2(s) BeO(s) + H2O(g) H = +54 kJ mol–1 Mg(OH)2(s) MgO(s) + H2O(g) H = +81 kJ mol–1

2. The Hydroxides Example:
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 2. The Hydroxides Example: Ca(OH)2(s) CaO(s) + H2O(g) H = +109 kJ mol–1 Sr(OH)2(s) SrO(s) + H2O(g) H = +127 kJ mol–1 Ba(OH)2(s) BaO(s) + H2O(g) H = +146 kJ mol–1

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) Relative Solubility of the Sulphates(VI) and Hydroxides of s-Block Elements 1. Processes involved in Dissolution and their Energetics When an ionic solid dissolves in water  two processes are taking place

1. Processes involved in Dissolution and their Energetics
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 1. Processes involved in Dissolution and their Energetics Two processes are 1. the breakdown of the ionic lattice 2. the subsequent stabilization of the ions by water molecules (this process is called hydration)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 1. Processes involved in Dissolution and their Energetics When an ionic solid dissolves in water  there must be energetically favourable interactions between the water molecules and the dissolved ions

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 1. Processes involved in Dissolution and their Energetics These interactons  compensate for the breaking of ionic bonds present in the ionic lattice  considered from the point of view of energetics

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 1. Processes involved in Dissolution and their Energetics The first process  involves an absorption of energy  break down the ionic lattice

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 1. Processes involved in Dissolution and their Energetics The second process  involves a release of energy  the ions are hydrated

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 1. Processes involved in Dissolution and their Energetics Example: The dissolution of sodium chloride in water

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 1. Processes involved in Dissolution and their Energetics The enthalpy change of solution of sodium chloride = +4 kJ mol–1  when one mole of sodium chloride is completely dissolved in a sufficiently large volume of solvent to form an infinitely dilute solution

NaCl(s)  Na+(g) + Cl–(g)
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.63) 1. The sodium chloride solid lattice is broken down to give its constituent ions in the gaseous state NaCl(s)  Na+(g) + Cl–(g)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 1. The sodium chloride solid lattice is broken down to give its constituent ions in the gaseous state The enthalpy change  accompanies this process is the reverse of the lattice enthalpy of sodium

The lattice enthalpy of sodium chloride = –776 kJ mol–1
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 1. The sodium chloride solid lattice is broken down to give its constituent ions in the gaseous state The lattice enthalpy of sodium chloride = –776 kJ mol–1

The enthalpy change of the above process = +776 kJ mol–1
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 1. The sodium chloride solid lattice is broken down to give its constituent ions in the gaseous state The enthalpy change of the above process = +776 kJ mol–1 NaCl(s)  Na+(g) + Cl–(g) H = +776 kJ mol–1

2. The hydration of the resulting ions
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 2. The hydration of the resulting ions The enthalpy change of hydration is the enthalpy change accompanies the hydration of one mole of both of these gaseous ions. Na+(g) + Cl–(g)  Na+(aq) + Cl–(aq) H = –772 kJ mol–1

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 2. The hydration of the resulting ions According to Hess’s law

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 2. The hydration of the resulting ions The enthalpy change of solution: Hsoln = Hhyd – Hlattice

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 2. The hydration of the resulting ions For a salt to be soluble in water  its enthalpy change of solution has to be a negative or a small positive value Let's Think 5

2. Relative Solubility of the Sulphates(VI) and Hydroxides
40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 2. Relative Solubility of the Sulphates(VI) and Hydroxides The sulphates(VI) and hydroxides of Group I metals  more soluble in water than those of Group II metals

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 2. Relative Solubility of the Sulphates(VI) and Hydroxides Group I metal ions  larger sizes  smaller charge

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) 2. Relative Solubility of the Sulphates(VI) and Hydroxides The Hlattice of their compounds  smaller in magnitude than those of Group II compounds  the dissolution of Group I compounds is more exothermic  the enthalpy changes of solution are more negative

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides For the sulphates(VI) of Group II metals  the cations are much smaller than the anions

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides The Hlattice is mainly determined by  the reciprocal of the sum of cationic and anionic radii (i.e )

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides The large ionic radius of the anion  the much smaller sizes of cations  relatively insignifiant in contributing to the sum of r + and r –

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides Going down the group  the increase in size of the cations does not cause a significant change in the Hlattice

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides The increase in size of the cations  cause the Hhyd to become less negative

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides That is to say  the decrease in Hhyd is more significant than the decrease in Hlattice  the Hsoln becomes less negative  the solubility of the sulphates(VI) of Group II metals decreases

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides For the hydroxides of Group II metals  the sizes of anions and cations are of the same order of magnitude

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides Again  the Hlattice is proportional to

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides Going down the group  cationic size increases  the change in Hhyd is comparatively small  less energy is required to break down the ionic lattice (i.e. the Hlattice becomes less negative)

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides That is to say  the decrease in Hlattice is more significant than the decrease in Hhyd

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) 2. Relative Solubility of the Sulphates(VI) and Hydroxides The Hsoln  becomes more negative  the solubility of the hydroxides of Group II metals increases Check Point 40-3

The END

Metals are sometimes referred to as electropositive elements. Why?
40.1 Characteristic Properties of the s-Block Elements (SB p.40) Let's Think 1 Metals are sometimes referred to as electropositive elements. Why? Answer They have low electronegativity values. Back

Let's Think 2 s-Block compounds give a characteristic flame colour in the flame test. Based on this, can you give one use of s-block compounds? Answer s-Block compounds can be used in fireworks. Back

Check Point 40-1 (a) Which ion has a greater ionic radius, potassium ion or calcium ion? Explain your answer. Answer (a) Potassium ion (0.133 nm) has a greater ionic radius than calcium ion (0.099 nm) . In fact, potassium ion and calcium ion are isoelectronic and have the same number of electron shells. However, calcium ion has one more proton than potassium ion, the electron cloud of calcium ion will experience greater attractive forces from the nucleus. This leads to a smaller ionic radius of calcium ion.

Check Point 40-1 (b) Explain why Group I elements show a fixed oxidation state of +1 in their compounds in terms of ionization enthalpies. Answer

(b) Group I elements form ions with an oxidation state of +1 only. It is because they have only one outermost shell electron. Once this outermost shell electron is removed, a stable fully-filled electronic configuration is obtained. Therefore, the first ionization enthalpies of Group I elements are low. The second ionization involves the removal of an electron from an inner electron shell. Once this electron is removed, the stable electronic configuration will be disrupted. Therefore, their second ionization enthalpies are very high. As a result, Group I elements form predominantly ionic compounds with non-metals by losing their single outermost shell electron, and they form ions having a fixed oxidation state of +1.

Check Point 40-1 (c) Ions of Group I and Group II elements have a very low tendency to form complexes. Give one reason to explain your answer. Answer (c) As ions of Group I and Group II elements do not have low-lying vacant orbitals available for forming dative covalent bonds with the lone pair electrons of surrounding ligands, they rarely form complexes.

Check Point 40-1 (d) Give one test which would enable you to distinguish a sodium compound from a potassium compound. Answer (d) Sodium compounds and potassium compounds can be distinguished by conducting a flame test. In the flame test, sodium compounds give a golden yellow flame, while potassium compounds give a lilac flame. Back

What is a dative covalent bond? How is it formed?
40.1 Characteristic Properties of the s-Block Elements (SB p.48) Let's Think 3 What is a dative covalent bond? How is it formed? Answer A dative covalent bond is a covalent bond in which the shared pair of electrons is supplied by only one of the bonded atoms. A dative covalent bond is formed by the overlapping of an empty orbital of an atom with an orbital occupied by a lone pair of electrons of another atom. Back

Check Point 40-2A (a) (i) List the factors that affect the value of the ionization enthalpy of an atom. Answer (a) (i) There are four main factors affecting the magnitude of the ionization enthalpy of an atom. They are the electronic configuration of an atom, the nuclear charge, the screening effect, and the atomic radius.

Check Point 40-2A (a) (ii) Why is ionization enthalpy of an atom always positive? Answer (a) (ii) Ionization enthalpy of an atom always has a positive value because energy is required to overcome the attractive forces between the nucleus and the electron to be removed.

Check Point 40-2A (a) (iii) Describe the general trend of the first and second ionization enthalpies down Group I of the Periodic Table. Answer

(a) (iii) The first ionization enthalpies of Group I elements are relatively low. The outermost s electron is located in a new electron shell. The attractive force between this s electron and the nucleus is relatively weak. Also, this s electron is effectively shielded from the attraction of the nucleus by the fully-filled inner electron shells. Once this electron is removed, a stable octet or duplet electronic configuration is obtained. Consequently, this s electron is relatively easy to be removed, and hence the first ionization enthalpies of Group I elements are relatively low. However, the second ionization of Group I elements involves the loss of an inner shell electron which is closer to the nucleus. The removal of this electron disrupts the stable electronic configuration. Therefore, the second ionization enthalpies of Group I elements are extremely high.

Check Point 40-2A (b) (i) List the factors that affect the value of the hydration enthalpy of an ion. Answer (b) (i) The value of the hydration enthalpy of an ion depends on the size and the charge of the ion.

Check Point 40-2A (b) (ii) Why does hydration enthalpy of an ion always have a negative value? Answer (b) (ii) Hydration enthalpy of an ion always has a negative value because it is the amount of energy released resulting from the attraction between the ion and water molecules.

Check Point 40-2A (b) (iii) Describe the general trend of the hydration enthalpy down Group II of the Periodic Table. Answer (b) (iii) Going down Group II, the hydration enthalpy of the ions decreases (becomes less negative). Since the ions get larger in size on moving down the group, the charge density of the ions falls. As a result, the electrostatic attraction between the ions and water molecules becomes weaker, and the hydration enthalpy becomes less negative down the group. Back

Let's Think 4 The burning of lithium, sodium and potassium in oxygen gives different types of oxides. Why do the metals behave differently? Answer

Back 40.2 Variation in Properties of the s-Block Elements (SB p.57)
On burning in air, lithium forms only lithium oxide, and it does not form the peroxide or superoxide. This is because the size of lithium ion is very small, leading to its high polarizing power. When a peroxide ion or superoxide ion approaches a lithium ion, the electron cloud of the peroxide ion or superoxide ion (large in size) would be greatly distorted by the lithium ion. The greater the distortion of the electron cloud, the lower the stability of the compound. That is why lithium peroxide and lithium superoxide do not exist. Sodium ion has a larger size than lithium ion. Its lower polarizing power allows it to form the peroxide when sodium is burnt in air. Potassium ion has a much larger size, so it has relatively low polarizing power. The electron cloud of the peroxide ion or superoxide ion would not be seriously distorted by potassium ion. This allows the peroxide ions or superoxide ions to pack around potassium ion with a higher stability. As a result, potassium is able to form stable peroxide or superoxide on burning in air. Back

Check Point 40-2B (a) Suggest a reason why the reaction of lithium with water is less vigorous than those of sodium and potassium. Answer (a) The reactivity of Group I metals with water is related to the relative ease of the metal atoms to lose the outermost shell electron. Going down the group, as the atomic size increases, the outermost shell electron becomes easier to be removed. Therefore, the reactivity of Group I metals towards water increases down the group. Lithium reacts with water vigorously. Sodium reacts with water violently and moves on the water surface with a hissing sound.

Check Point 40-2B (b) Which element is the strongest reducing agent, calcium, strontium or barium? Answer (b) Barium is the strongest reducing agent. It is because the reducing power of an element is related to the ease of the atom to lose the outermost shell electron. Since barium has larger atomic sizes, its outermost shell electrons are less firmly held by the nucleus. Therefore, barium has a higher tendency to lose its outermost shell electrons than both calcium and strontium. Back

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.64) Let's Think 5 The value of Hsoln of a solid does not indicate whether the solid is soluble in water or not. So how can we predict the solubility of a solid in water? Answer Generally speaking, for a solid to be soluble in water, its enthalpy change of solution has to be a negative or a small positive value. Back

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) Check Point 40-3 (a) Give balanced chemical equations for the following reactions: (i) Thermal decomposition of barium carbonate (ii) Reaction between sodium peroxide and water (iii) Reaction between calcium oxide and dilute hydrochloric acid Answer (a) (i) BaCO3(s)  BaO(s) + CO2(g) (ii) Na2O2(s) + 2H2O(l)  2NaOH(aq) + H2O2(aq) (iii) CaO(s) + 2HCl(aq)  CaCl2(aq) + H2O(l) 

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) Check Point 40-3 (b) Suggest a reason why barium sulphate(VI) is insoluble in water, while potassium sulphate(VI) is soluble in water although they have cations of similar sizes and the same anion. (The ionic radii of potassium ion and barium ion are nm and nm respectively.) Answer

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) (b) When an ionic solid dissolves in water, two processes are taking place. They are the breakdown of the ionic lattice and the subsequent stabilization of the ions by water molecules. The enthalpy change involved in the whole dissolution process is known as the enthalpy change of solution, Hsoln, which is equal to Hsoln = Hhyd – Hlattice. For an ionic compound to be soluble in water, the enthalpy change of solution has to be a negative or a small positive value. The reason why barium sulphate(VI) is insoluble in water while potassium sulphate(VI) is soluble in water is that potassium ion has a smaller charge than barium ion. The Hlattice of potassium sulphate(VI) is smaller in magnitude (less negative) than that of barium sulphate(VI). As a result, the enthalpy change of solution of potassium sulphate(VI) is more negative, and hence it is soluble in water while barium sulphate(VI) is not.

40.3 Variation in Properties of the Compounds of the s-Block Elements (SB p.65) Check Point 40-3 (c) Compare the solubility of calcium sulphate(VI) and barium sulphate(VI) in water. Explain your answer. Answer (c) Calcium sulphate(VI) is expected to be more soluble than barium sulphate(VI). It is because calcium ion has a smaller size than barium ion. This causes the Hhyd of calcium sulphate(VI) to be more negative than that of barium sulphate(VI). As a result, the Hsoln of calcium sulphate(VI) becomes more negative than that of barium sulphate(VI), and hence calcium sulphate(VI) is more soluble in water than barium sulphate(VI). Back

40 The s-Block Elements 40.1 Characteristic Properties of the s-Block Elements 40.2 Variation in Properties of the s-Block Elements 40.3 Variation in.

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40 The s-Block Elements 40.1 Characteristic Properties of the s-Block Elements 40.2 Variation in Properties of the s-Block Elements 40.3 Variation in.

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Presentation on theme: "40 The s-Block Elements 40.1 Characteristic Properties of the s-Block Elements 40.2 Variation in Properties of the s-Block Elements 40.3 Variation in."— Presentation transcript:

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