1. Lection 11. Chemical elements and their classification
Lection 11. Chemical elements and their classification. S-block of IA group of elements. Hydrogen
PhD Falfushynska Halina

3. Periodic Patterns
The chemical behavior of elements is determined by its electron configuration
Energy levels are quantized so roughly correspond to layers of electrons around the nucleus.
A shell is all the electrons with the same value of n.
n is a row in the periodic table.
Each period begins with a new outer electron shell

4. Each period ends with a completely filled outer shell that has the maximum number of electrons for that shell.
The number identifying the A families identifies the number of electrons in the outer shell, except helium
The outer shell electrons are responsible for chemical reactions.
Group A elements are called representative elements
Group B elements are called transition elements.

5. Chemical “Families”
IA are called alkali metals because the react with water to from an alkaline solution
Group IIA are called the alkali earth metals because they are reactive, but not as reactive as Group IA.
They are also soft metals like Earth.
Group VIIA are the halogens
These need only one electron to fill their outer shell
They are very reactive.
Group VIIIA are the noble gases as they have completely filled outer shells
They are almost non reactive.

6. Four chemical families of the periodic table: the alkali metals (IA), the alkaline earth metals (IIA), halogens (VII), and the noble gases (VIIIA).

7. Metal: Elements that are usually solids at room temperature
Metal: Elements that are usually solids at room temperature. Most elements are metals.
Non-Metal: Elements in the upper right corner of the periodic
Table. Their chemical and physical properties are different
from metals.
Metalloid: Elements that lie on a diagonal line between the
Metals and non-metals. Their chemical and physical
properties are intermediate between the two.

8. Elements with 1, 2, or 3 electrons in their outer shell tend to lose electrons to fill their outer shell and become cations.
These are the metals which always tend to lose electrons.
Elements with 5 to 7 electrons in their outer shell tend to gain electrons to fill their outer shell and become anions.
These are the nonmetals which always tend to gain electrons.
Semiconductors (metalloids) occur at the dividing line between metals and nonmetals.

9. Cs 133 55 Atomic number = protons and electrons
How many protons, neutrons and electrons are found in an atom of
133 55 Cs
Atomic number = protons and electrons
There are 55 protons and 55 electrons
Mass number = sum of protons and neutrons
133 – 55 = 78
There are 78 neutrons

10. Members of the s-Block ElementsLi Be Na K Rb Cs Fr Mg Ca Sr Ra Ba
IA IIA
IA Alkali metals
IIA Alkaline Earth
metals

11. Physical Properties
The alkali metals are soft, with low melting and boiling temperatures.
They have low densities - Li, Na and K are less dense than water.
They have low standard enthalpies of melting and vaporization.
They show relatively weak metallic bonding as only one electron is available from each atom.
Alkali metals colour flames.
The ionic radii of the alkali metals are all much smaller than the corresponding atomic radii. This is because the atom contains one electron in an s level relatively far from the nucleus in a new quantum shell, and when it is removed to form the ion the remaining electrons are in levels closer to the nucleus.
The metal thus obtained is 99% pure and is preserved by keeping it wrapped in paraffin wax.

12. Metallic character High tendency to lose e- to form positive ions
Metallic character increases down both groups

13. Electronegativity Low nuclear attraction for outer electrons
Highly electropositive
Small electronegativity
Group I Li Na K Rb Cs Fr

14. Predominantly ionic with fixed oxidation state
Most electropositive metals.
Low first I.E. and extremely high second I.E.
Form predominantly ionic compounds with non-metals by losing one electron.
Fixed oxidation state of +1.

15. Flame test Li deep red Na yellow K lilac Rb bluish red Cs blue
Na+ Cl- (g)  Na (g) + Cl (g)
Na(g)  Na* (g)
[Ne]3s [Ne]3p1
Na*(g)  Na(g) + h (589nm, yellow)
Flame test
Li deep red
Na yellow
K lilac
Rb bluish red
Cs blue
HCl(aq)
sample

16. Weak tendency to form complex
Complex formation is a common feature of d-block
element. e.g. Co(NH3)63+ Co
:NH3
H3N:
s-block metal ions have no low energy vacant
orbital available for bonding with lone pairs
of surrounding ligands, they rarely form complexes.

17. Atomic radii (nm) Ionization Enthapy Group I 1st I.E. 2nd I.E. Li 519
7300 Na
494
4560 K
418
3070 Rb
402
2370 Cs
376
2420 Li
0.152 Na
0.186 K
0.231 Rb
0.244 Cs
0.262 Fr
0.270
Ionization Enthapy
Diagonal relationship of lithium with magnesium on the basis of polarizing power, electronegativity and covalent nature

18. Variation in Melting Points
Note: The exceptionally high m.p. of calcium
is due to contribution of d-orbital participation
of metallic bonding.
250
500
750
1000
1250 Be Mg Ca Sr Ba Li Na K Rb Cs

19. Occurrence and Extraction
These elements are too reactive to be found free in nature. Sodium occurs mainly as NaCI (salt) in sea-water and dried-up sea beds. Potassium is more widely distributed in minerals such as sylvite, KCI, but is also extracted from sea-water. The alkali metals are so reactive they cannot be displaced by another element, so are isolated by electrolysis of their molten salts.

20. Electrolysis of Lithium chloride
A mixture of dry lithium chloride (55%) and potassium chloride (45%) is fused and electrolysed in an electrolytic cell shown in the figure.
Potassium chloride is added to increase the conductivity of lithium chloride and to lower the fusion temperature. The cell is operated at a temperature of about 723 K and voltage of 8-9 volts is applied.     
At cathode:  Li+ + e- → Li
At anode :  2CI- - 2e- → CI2

21. Basic oxides, hydroxides
Li2O
LiOH
Na2O, Na2O2
NaOH
K2O2, KO2
KOH
Rb2O2, RbO2
RbOH
Cs2O2, CsO2
CsOH
Reaction with water:
Oxide: O2- + H2O  2OH-
Peroxide: O H2O  H2O2 + 2OH-
Superoxide: 2O2- + 2H2O  2OH- + H2O2 + O2
Strength increase
:O:.O:
.. ..
Super oxide
:O:O:
.. ..
Peroxide ion

22. Experimentally and theoretically proved that alkali metals can form covalent diatonic molecule M2. Alkali metals containing approximately 1% of M2. Li2 molecule can exist and does exist, because the binding effect dominates the effect of break and the energy of Li-Li is quite large (25.8 kcal / mol).
Among the heteronuclear alkali-metal fermionic species, LiNa is the least reactive, whereas LiCs is the most reactive. For the bosonic species, LiK is the most reactive in zero field, but all species considered, LiNa, LiK, LiRb, LiCs, and KRb, share a universal reaction rate once a sufficiently high electric field is applied. (Phys. Rev. A 84, (2011)).

23. Reactions with oxygen Normal Oxide Peroxide Superoxide Formed by Li Na
S-block elements are strong reducing agents.
Their reducing power increases down both groups.
(As the atomic size increases, it becomes easier to
remove the outermost electron)
S-block elements reacts readily with oxygen.
they have to be stored under liquid paraffin
to prevent contact with the atmosphere.
Normal Oxide
Peroxide
Superoxide
Formed by Li Na
K, Rb, Cs

24. Reaction with hydrogen
Reaction with water
Reaction with hydrogen
M(s)  M+(aq) + e-
H2O(l) + e-  OH-(aq) + ½ H2(g)
All the IA elements react directly with hydrogen.
2Na(s) + H2(g)  2NaH(s)
The reactivity increases down the group.
The hydrides are ionic.
Although lithium has highly negative Eo, it only
reacts slowly with water. This illustrates the importance of the role of kinetic factors in determining the rate of a chemical reaction.
The spontaneously inflammable silicone hydride reacts with the oxygen of the air.
SiH4 + 2 O2==> SiO2 + 2 H2O     

25. Reaction with chlorine
Reactions of chlorides
All the s-block metals react directly with chlorine to produce chloride.
2Na(s) + Cl2(g)  2NaCl(s)
All group I chlorides are ionic.
All group I chlorides are ionic and readily soluble in water. No hydrolysis occurs.

26. Reactions of oxides and hydroxides
All group I oxides reacts with water to form
hydroxides
Oxide: O2- + H2O  2OH-
Peroxide: O H2O  H2O2 + 2OH-
Superoxide: 2O2- + 2H2O  2OH- + H2O2 + O2
All group I oxides/hydroxides are basic and the
basicity increases down the group.

27. Reactions of hydrides They all react readily with water to give the
metal hydroxide and hydrogen due to the
strong basic property of the hydride ion, H:-
H:-(s)+ H2O(l)  H2(g)+ OH-(aq)
Hydride ions are also good reducing agent.
They can be used to prepare complex hydrides
such as LiAlH4 and NaBH4 which are used to
reduce C=O in organic chemistry.

28. Solvay process
The Solvay process results in soda ash (sodium carbonate (Na2CO3)) from brine (NaCl) and from limestone (as a source of calcium carbonate (CaCO3)). The overall process is: 2 NaCl + CaCO3 → Na2CO3 + CaCl2
1. In the first step in the process, CO2 passes through a concentrated aqueous solution of NaCl and ammonia (NH3).
NaCl + CO2 + NH3 + H2O → NaHCO3 + NH4Cl (I)
2. The CaCO3 in the limestone is partially converted to quicklime CaO and CO2:
CaCO3 → CO2 + CaO (II)
3. The sodium bicarbonate (NaHCO3) that precipitates out in reaction (I) is filtered out from the hot NH4Cl solution, and the solution is then reacted with the CaO left over from heating the limestone in step (II).
2 NH4Cl + CaO → 2 NH3 + CaCl2 + H2O (III)
CaO makes a strong basic solution. The NH3 from reaction (III) is recycled back to the initial brine solution of reaction (I).
The NaHCO3 precipitate from reaction (I) is then converted to the final product, Na2CO3, by calcination ( C), producing water and carbon dioxide as byproducts:
2 NaHCO3 → Na2CO3 + H2O + CO2 (IV)

29. Thermal Stability of carbonates and hydroxides
Thermal stability refers to decomposition of the compound on heating. Increased thermal stability means a higher temperature is needed to decompose the compound.
Li2CO3  Li2O + CO2 ( at 700oC)
All other group I carbonates are stable at ~800oC
All group I hydroxides are stable except LiOH
at Bunsen temperature (lies between degrees Celsius).

30. Uses of s-block compounds
Sodium carbonate
Manufacture of glass
Water softening
Paper industry
Sodium hydrocarbonate
Baking powder
Soft drink

31. Alkali metals in farmacy
Lithium stearate is mixed with oils to make all-purpose and high-temperature lubricants
Lithium carbonate has a sedative effect. It is highly effective in preventing attacks of depression or mania, by stabilising your chemistry.
Potassium bromide, KBr, was used as an antaphrodisiac
Potassium permanganate, KMnO4, is an important oxidizing, antiseptic and antidote agent
Baking soda (NaHCO3) due to its extremely basic is an especially good antacid and is used in products such as Alka-Seltzer. Important: Children under the age of 6 should not take any antacid medicines unless prescribed by a doctor.
Drinking soda with a medicine pill make it dissolve faster once it is swallowed .

32. Alkali metals Poisoning
External exposure to large amounts of Cs-137 can cause burns, acute radiation sickness and even death. Exposure to Cs-137 can increase the risk for cancer because of exposure to high-energy gamma radiation. Internal exposure to Cs-137, through ingestion or inhalation, allows the radioactive material to be distributed in the soft tissues, especially muscle tissue, exposing these tissues to the beta particles and gamma radiation and increasing cancer risk.

33. Alkali metals analysis
Na+ + [Sb(OH)6]  Na[Sb(OH)6] – white crystalline precipitate
Na+ + Zn(CH3COO)2 + 3UO2(CH3COO)2 + CH3COO– + 9H2O  NaCH3COOZn(CH3COO)23UO2(CH3COO)29H2O – green-yellow precipitate
KCl + NaHC4H4O6  KHC4H4O6 + NaCl – white crystalline precipitate
2K+ + Na+ + [Co(NO2)6]3–  K2Na[Co(NO2)6] – yellow precipitate;

34. Hydrogen is the simplest of all elements

35. Production of hydrogen
As the reaction between a metal and acid produces hydrogen, we can place this reaction in a flask that is connected to a delivery tube, that will allow hydrogen to pass through it ending up in a water trough, hydrogen will try to escape by bubbling up into the glass jar

36. Extraction of Hydrogen
Zn + 2HCl  ZnCl2 + H2
Al + NaOH + 3H2O  Na[Al(OH)4] + 3/2 H2
2Na + 2H2O  2NaOH + H2
СaH2 + 2H2O  2Ca(OH)2 + H2
С + 2H2O  СO + H2

37. Properties of hydrogen
Colorless: - can’t be see
Odorless: - has no small
Tasteless: - doesn’t have a taste
Gas: - found in gas state, not liquid, or solid
Lightest gas: - least density, lighter then air
Explosive: - H2 + O H2O + energy
reactants combine causing an explosion

38. Chemical properties of Hydrogen
Hydrogen is slightly more soluble in organic solvents than in water.
It does not usually react with other chemicals at room temperature.
Hydrogen reacts with oxygen:
2Н2 + О2  2Н2О; Н2 + hν  2Н; Н2 + О2  2ОН
ОН + Н2  Н2О + Н
Hydrogen is a good reducing agent: CuO + H2  Cu + Н2О
Hydrogen also forms ionic bonds with some metals, creating a compound called a hydride: Ca + H2  CaH2
Hydrogen reacts with non-metals: 3Н2 + N2  2NH3; H2 + Cl2  2HCl

39. Group 1A – The alkali metals
Some facts…
1) These metals all have ___ electron in their outer shell
2) Reactivity increases as you go _______ the group. This is because the electrons are further away from the _______ every time a _____ is added, so they are given up more easily.
3) They all react with water to form an alkali (hence their name) and __________, e.g:
Potassium + water potassium hydroxide + hydrogen
2K(s) H2O(l) KOH(aq) H2(g)
Words – down, one, shell, hydrogen, nucleus