2(1869) Dmitri Mendeleev(Russian chemist) shows a first version of the periodic table. He noticed thatclassifying theelements bytheir atomic massa periodicity in certain properties could be seen. The first table consisted of 63 elements.Periodicity: the regular repeating of properties according to the arrangement of elements in the PT.
3*Henry Mosely(British) discovered nuclear charges of all known elements and that chemical properties of elements are related to their atomic numbers but not atomic weights.
4He stated that elements should be arranged in order of increasing atomic numbers. So, today’s periodic table was formed.
5In modern periodic table, elements are listed in order of increasing atomic numbers. Elements with similar chemical properties are placed in the same vertical columns.
91A:Alkali metals 2A:Alkaline earth metals 3A:Earth metals 4A:Carbon Family 5A:Nitrogen Family 6A:Oxygen Family 7A:Halogens 8A:Noble(Inert)gases
10GROUPS/FAMILIES: The vertical columns Elements in the same group have -similar chemical properties(exception:H in 1A group)-Same number of valence electronsand orbitals.(exception:He in 8A group)- The effective nuclear charge (the charge acting on valence electrons) is the same.(exception:He in 8A group)
11* *For A groups; # of valence electrons= # of the group(except He in 8A) in 7A;number of valence electrons=7 However, we can’t say the same thing for B groups. *Lanthanides&Actinides belong to 3B group(the biggest group including 32 elements)
12PERIODS: The horizontal rows There are 7 periods Valence shell determines the period numberEach of them starts with a metal and ends with a noble gas.(except first and seventh ones)Elements in the same period have the same # of energy levels or shells or principle quantum numbers.
14Radius of an atom: Half the distance between two nuclei. 2)ATOMIC RADIUS:Radius of an atom: Half the distance between two nuclei.Br Br2rCovalent radius: Half the distance between two nuclei in a covalent molecule consisting of identical atoms.Van der Waals radius: This is for 0 group gases.Ionic radius: This for ions in an ionic compound.in 1920, shortly after it had become possible to determine the sizes of atoms using X-ray crystallography . graphy is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographercan produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder and various other information. this method determined the size of atoms, the lengths and types of chemical bon ds.
152)ATOMIC RADIUS:Atomic size (volume,radius) is affected by mainly two factors in the periodic table:1)The # of shells (as it increases, atomic volume also increases)2)Nuclear charge(as the p+ # increases, atomic volume decreases)
16Atomic volume decreases Li Be B C N O FNaWHY?Within the same period;All the elements have the same # of shells but the p+ # increases from left to right.Therefore,atomic radius decreases from left to right.K
19IONIC VOLUME: X X+ X+2 X- X-2 Proceeding down a group; The # of shells of atoms increases but the p+ # of atoms also increases.However,the increase in shells makes a bigger effect on the radius than the nuclear charge.Therefore, the atomic volume or radius increases down a group.IONIC VOLUME:XX+X+2X-X-2
21For isoelectronic species; The greater the nuclear charge,the smaller the radius(or volume)7N-3,8O-2,11Na+,13Al+3 are isoelectronics.The relationship between their radii;7N-3 >8O-2 >11Na+ >13Al+3
22!!!It’s not the IE(bec. X is a solid and molecular) 3)IONIZATION ENERGY: The minimum amount of energy required to remove the most losely bound e-s from a mole of gaseous atoms is called “the ionization energy(I).” X(g) + I X+(g) + e- WARNING!!! X2(s)+I X+(s) + e-!!!It’s not the IE(bec. X is a solid and molecular)
233)IONIZATION ENERGY:The energy required to remove (1 mole of) the first electron from 1 mole of gaseous atom is called the first ionization energy.
24Ionization EnergyThe second ionization energy is the energy required to remove (1 mole of) the second electron(s).Always greater than first IE.The third IE is the energy required to remove a third electron.Greater than 1st or 2nd IE.
25What determines IE The greater the nuclear charge, the greater IE. The greater the effective nuclear charge, the greater IE.Greater distance from nucleus (atomic radius) decreases IEShielding of electrons in filled inner orbitals
26Atomic volume decreases& IE generally increases ***Because I of d block elements are irregular, rules that we talk about the IE belong to A group elements. The variation of first ionization energies within the same period: As the atomic volume increases, the attraction of the nucleus on the electrons decreases. *Ionization energies in the same period: Noble gases > nonmetals > metalsAtomic volume decreases& IE generally increases
27Ionization energyAll the atoms in the same period have the same energy level.Same shielding.But, increasing nuclear charge and effective nuclear charge, ENC.So IE generally increases from left to right.
28The variation of IE within the same group: ***In the same period from left to right the ionization energies: 1A < 3A < 2A < 4A < 6A < 5A < 7A < 8AirregularitiesThe variation of IE within the same group:Down the group, atomic volumes of elements increase and more shielding effect, same ENC.Therefore, the IE of elements decrease in the same group from top to bottom.
29He has a greater IE than H. same shielding greater nuclear charge First Ionization energyAtomic number
30Outer electron further away outweighs greater nuclear charge Li has lower IE than HOuter electron further awayoutweighs greater nuclear chargeHFirst Ionization energyOutweigh:to exceed in importanceLiAtomic number
31greater nuclear charge HeBe has higher IE than LiSame shieldinggreater nuclear chargeFirst Ionization energyHBeLiAtomic number
32B has greater shielding greater nuclear charge HeB has lower IE than BeB has greater shieldinggreater nuclear chargep orbital is slightly more diffuse and its electron easier to removeFirst Ionization energyHBeBLiAtomic number
33First Ionization energy HeFirst Ionization energyHCBeBLiAtomic number
34First Ionization energy HeNFirst Ionization energyHCBeBLiAtomic number
35First Ionization energy HeBreaks the pattern, because the outer electron is paired in a p orbital and experiences inter-electron repulsion.NFirst Ionization energyHCOBeBLiAtomic number
36First Ionization energy HeFNFirst Ionization energyHCOBeBLiAtomic number
37Ne has a lower IE than He Both are full, Ne has more shielding Greater distanceFNFirst Ionization energyHCOBeBLiAtomic number
38Na has a lower IE than Li Both are s1 Na has more shielding HeNeNa has a lower IE than LiBoth are s1Na has more shieldingGreater distanceFNFirst Ionization energyHCOBeBLiNaAtomic number
40Why the drop between groups IIA and IIIA(Be-B)? The explanation lies with the structures of Boron and Aluminium. The outer electron is removed more easily from these atoms than the general trend in their period would suggest.Be1s22s21st I.E. = 900 kJ mol-1B1s22s22px11st I.E. = 799 kJ mol-1
41You might expect the Boron value to be more than the Beryllium value because of the extra proton. Offsetting that is the fact that Boron's outer electron is in a 2p orbital rather than a 2s. 2p orbitals have a slightly higher energy than the 2s orbital, and the electron is, on average, to be found further from the nucleus. This has two effects.The increased distance results in a reduced attraction and so a reduced ionisation energy.Offset:counterbalance.
42The 2p orbital is screened not only by the 1s2 electrons but, to some extent, by the 2s2 electrons as well. That also reduces the pull from the nucleus and so lowers the ionisation energy.
43Why the drop between groups IIA and IIIA(Mg-Al)? The explanation for the drop between Magnesium and Aluminium is the same, except that everything is happening at the 3-level rather than the 2-level.12Mg1s22s22p63s21st I.E. = 736 kJ mol-113Al1s22s22p63s23px11st I.E. = 577 kJ mol-1
44The 3p electron in Aluminium is slightly more distant from the nucleus than the 3s, and partially screened by the 3s2 electrons as well as the inner electrons. Both of these factors offset the effect of the extra proton.
45If the outer electron looks in towards the nucleus, it doesn't see the nucleus sharply. Between it and the nucleus there are the two layers of electrons in the first and second levels. The 11 protons in the sodium's nucleus have their effect cut down by the 10 inner electrons. The outer electron therefore only feels a net pull of approximately 1+ from the centre.This lessening of the pull of the nucleus by inner electrons is known as screening or shielding.
46Why the drop between groupsVA and VIA (N-O and P-S)? Once again, you might expect the ionisation energy of the group VIA element to be higher than that of group VA because of the extra proton. What is offsetting it this time?7N: 1s22s22px12py12pz1 1st I.E. = 1400 kJ mol-18O: 1s22s22px22py12pz1 1st I.E. = 1310 kJ mol-1
47Two electrons in the same orbital experience a bit of repulsion from each other. This offsets the attraction of the nucleus, so that paired electrons are removed rather more easily than you might expect.
48The screening is identical (from the 1s2 and, to some extent, from the 2s2 electrons), and the electron is being removed from an identical orbital.The difference is that in the Oxygen case the electron being removed is one of the 2px2 pair. The repulsion between the two electrons in the same orbital means that the electron is easier to remove than it would otherwise be.The drop in ionisation energy at Sulphur is accounted for in the same way.
51***We can decide about the group number of A group elements by considering their ionization energy values. Mg(g)(1s22s22p63s2)+I1(176Kcal/mole) Mg+(g) + e-Mg+(g)(1s22s22p63s1)+ I2(348Kcal/mole) Mg+2(g)+ e- Mg+2(g) (1s22s22p6)+ I3(1847Kcal/mole) Mg+3(g)+ e- 1st&2nd IE for Mg atom belong to the removal of valence electrons which are bounded very weakly to the nucleus .However,3rd e- requires considerably more energy than the removal of valence e-s as it will experience higher ENC.
52WARNING!!!There is always needed much more energy to remove inner electrons than the outer electrons since the inner electrons will experience a higher ENC. The sharp jumps between ionization energies help us to find out group numbers of A group elements. We can say that Mg atom is in 2A group by considering the sharp increase between its second and third ionization energies.(because,there is very sharp increase between its 2nd&3rd ionization energies)
53electron being lost:1st nd rd th th th th(2A)(3A)(4A)(5A)(6A)
54The rare gases (He, Ne, Ar, Kr, Xe, Rn) appear at peak values of ionization energy, which reflect their chemical inertness, while the alkali metals (Li, Na, K, Rb, Cs) appear at minimum values of ionization energy, in keeping with their reactivity and ease of cation formation.
554)ELECTRON AFFINITY:The electron affinity is the energy that is released when an atom in the gas phase gains an electron and is thus converted to an anion, also in the gas phase:
56Electron affinities are difficult to measure and there is no reliable data available for most elements. However, the larger the atom, the lower its electron affinity, as shown with Group VII elements:
57For reasons outside the scope of this discussion, the electron affinity of Fluorine is an exception to this trend.
595) ELECTRONEGATIVITY:Electronegativity is the power of an atom to attract electron density in a covalent bond (Linus Pauling)
60Electronegativity + – H Cl 08/10/99+–Electronegativity describes how electrons are shared in a compoundConsider the compound HClHClThe electron clouds represent where the two electrons in the HCl bond spend their time (sizes of atoms are not being shown)The shared electrons spend more time around Cl than H. In other words Cl is more electronegative than H.
62Electronegativity H 2.1 He - Li 1.0 Be 1.5 B 2.0 C 2.5 N 3.0 O 3.5 F Pauling’s electronegativity scaleH2.1He-Li1.0Be1.5B2.0C2.5N3.0O3.5F4.0NeNa0.9Mg1.2AlSi1.8PSClAr
63These numbers are derived from several factors including EA, IE, atomic radius You do not need to understand where the numbers come fromYou need to know that a high number means the element has a greater pull on electrons
64Calculating EN differences 08/10/99The first step in defining the polarity of a bond is to calculate electronegativity difference ( EN) EN = EN large - EN smallE.g. for NaCl, EN = 3.2 –0.9 = 2.3, ionic.
65Bigger electronegativity, -Bigger tendency in gaining electrons.
66Summary Shielding is constant Ionization energy decreases Electronegativity decreasesNuclear charge increasesAtomic radius increasesShielding increasesIonic size increasesShielding is constantAtomic Radius decreasesIonization energy increasesElectronegativity increasesNuclear charge increases
67OXIDATION STATES OF ELEMENTS GroupIAIIAIIIAIVAVAVIAVIIAVIIIAMAX(+)+1+2+3+4+5+6+7NAMIN(-)-4-3-2-1
69Alkali Metals(IA)(except Fr): Groups of ElementsAlkali Metals(IA)(except Fr):Group 1A metalsSoft, silvery colored metals that react violently with H2O to form basic solutions- They have low melting points and densities due to being the largest atom in their period of the PT.Because of Fr’s short of supply and nuclear instability.
70Alkali Metals(IA)(except Fr): Going down the group, the metals get softer and mp decreases due to increase in atomic size.
71They are the most reactive of all the metals on the periodic table since they can easily lose their one e.Their rectivity also increases as you move down their family.Therefore; most reactive ones are: Cesium & Francium
72Because the elements are very reactive, they easily combine with water and Oxygen.Therefore, most of these elements are not found freely in nature.That is why they are stored in oil in a bottle in the laboratory in order to prevent any reaction with Oxygen.They tarnish (lose lustre) rapidly when exposed to the air.
73Chemical Reactions of Alkali Metals Reaction with water (Their rectivity increases as you move down the group)2Na(s) + H2O(l) Na+(aq) + 2OH- (aq) + H2(g)With lithium, the reaction occurs slowly and steadilyIn the case of sodium, the reaction is vigorous, producing enough heat to melt the sodium which fizzes around the surface quite vigorouslyWith potassium the reaction is violent and the heat produced is enough to ignite the hydrogen gas evolved, which burns with a purple flame.They produce alkaline solution and hydrogen gas as a result of the rxn w/ water.Fizz:give off bubbles of gas.
75They give caharacteristic colour in the flame(chemical peoperty). Alkali Metal FamilyNaLiKThey give caharacteristic colour in the flame(chemical peoperty).
76Chemical Reactions of Alkali Metals Reaction with oxygen,React with oxygen to produces oxides.4Li(s) + O2(g) Li2O(s)
77Chemical Reactions of Alkali Metals Reaction with halogensReaction with halogens produces salts2Na(s) + Cl2(g) 2NaCl(s)2K(s) + Br2(g) 2KBr(s)2Cs(s) + l2(g) 2CsI(s)
78HALOGENS(VIIA) except At: Exist as diatomic molecules in which atoms are joined by a single cov. bond.The elements in this group are referred to as Halogens because they produce salts when combined with alkali metals (e.g.NaCl).these salts are usually white & soluble in water.Because of At’s rarity and nuclear instability
79HALOGENS(VIIA) except At: They are all very reactive and quite electronegative nonmetals. The ease w/ which they gain electrons decreases going down the group.Halogens tend to be less reactive as you move down the group.Flourine is the most reactive Halogen and combines with other elements very readily.Oxidizing power decreases down the group.
80Most are Poisonous .When Fluorine combines with Na to form NaF,it is an effective cavity fighter that is added to toothpastes.Chlorine is a great bacteria fighter so it is used in swimming pools and household cleaning agents.Iodine is also useful for eliminating bacteria.Since it is not as reactive as Chlorine, it can be used on humans.
81HALOGENS(VIIA) except At: Going down the group, their physical state varies at room temp & pressure depending on the Van Der Waals force strength present between molecules since the molecules have different molecular mass values.F2, Cl2 -- gasBr2 --- liquidI2 -- solid, forms a purple gas on heating.They all need an electron to become stable, thus form negative ions
82HALOGENS(VIIA) except At: Are slightly soluble in water as they are non-polar molecules.Concentrated solutions of chlorine- green tingeSolutions of bromine- darken from yellow through orange to brown as the concentration increases.Iodine dissolved in non-polar solvents like hexane--violet solution.Iodine dissolved in polar solvents like water & ethanol--brown solution.Tinge:slight degree.
83HALOGENS(VIIA) except At: Halogens dissociate slightly in aqueous solutions, forming an acidic solution:Cl2(aq) + H2O(l) H+ (aq)+ Cl-(aq) + HOCl(aq)HOCl(hypochlorous acid): weak acid, reacts as an oxidant since it donates its one oxygen.It oxidises colored dyes to colorless products.HOCl turns blue litmus paper into red, and then make it colorless. Therefore, HOCl and OCl- are used in bleaches.They are also toxic to microbes.
84Displacement reactions of Halogens A more reactive halogen is capable of replacing less reactive one from its solutionCl2 reacts with Br- and I-Cl2(aq) + 2Br-(aq) 2Cl-(aq) + Br2(l)Cl2(aq) + 2I-(aq) 2Cl-(aq) + I2(s)Br2 reacts with I-Br2(aq) + 2I-(aq) 2Br-(aq) + I2(s)I2 non-reactive with halide ions
85HALOGENS(VIIA) except At: The common insoluble halides (ions of halogens) are those of Pb and Ag.PbI2 -- is a bright yellow colored, can be used as a test for iodide ion.Look at P. 77& 78 for the colors ofhalogens and testsof halide ions.
86Oxides of period 3 elements Metallic Oxides in Period 3 Sodium oxide: Na2O ionic Magnesium oxide: MgO ionic Aluminum oxide: Al2O3 ionic Metalloid oxide in Period 3 Silicon dioxide: SiO2 covalent Nonmetallic oxides in Period 3 Tetraphosphorus decoxide: P4O10 covalent Sulfur trioxide: SO3 covalent Dichlorine heptoxide: Cl2O7 covalent
87Discuss the changes in nature, from ionic to covalent and from basic to acidic, of the oxides across period 3.Acidic/BasicMetallic oxides in Period 3 are basicSodium oxide: Na2O + H2O 2 NaOH basicMagnesium oxide: MgO + H2O Mg(OH)2 basicNet ionic eqn: O2- + H2O 2 OH-Aluminum oxide: Al2O3 + 6HCl 2 AlCl3+ 3H2O amphotericAl2O3 +2 NaOH + 3H2O 2NaAl(OH)4
88Oxides of period 3 elements Metalloid oxide in Period 3 is acidicSilicon dioxide: SiO2 + H2O H2SiO3 acidic(silicic acid)Nonmetallic oxides in Period 3 are acidicTetraphosphorus decoxide: P4O H2O 4H3PO4 acidicSulfur trioxide: SO3 + H2O H2SO4 acidicDichlorine heptoxide: Cl2O7 + H2O 2HClO4 acidicArgon does not form an oxideSilicic:[suh-lis-ik]