For Group 13
(a) Atomic size On moving down the group for each successive member, one extra shell of electrons is added and therefore, atomic radius is expected to increase. However, a deviation can be seen.
Atomic radius of Ga is less than that of Al due to presence of additional 10d-electrons, which offer poor screening effect to the outer electron.
(b) Ionisation Enthalpy The ionisation enthalpy values are expected from general trends do not increase smoothly down the group. The decrease from B to Al is associated with increase in size.
The observed discontinued between Al and Ga and between In and Tl due to low screening effect of d and f-electrons which compensates increased nuclear charge.
(c) Metallic or Electropositive Character Boron is a semi-metal (metalloid) due to very high ionisation enthalpy. All others are metals and metallic character first increases from B to Al as size increases. From Al to Tl decrese due to poor shielding or d- and f-electrons.
(d) Oxidation States As we move down the group, the stability of +3 oxidation state decreases while that of +1 oxidation state progressively increases. In other words, the order of stability of +1 oxidation state increases in the order. Al<Ga(e) Nature of Halides These elements react with halogens to form trihalids (except TIl3)
Boron in halides are electron deficient molecules and behave as Lewis acids. The Lewis character decreases in the order : Bl3>BBr3>BCl3>BF3
For Group 14
(a) Atomic Size There is considerable increase in covalent radius from C to SI thereafter from Si to Pb as small increase in radius is observed. This is due to the presence of completely filled d and f-orbitals in heavier member.
(b) Ionisation Enthalpy The first ionisation enthalpy of group 14 members is higher than the corresponding members of group 13. The influence of inner core electrons is visible here. In general the ionisation enthalpy decreases down the group. Small decrease in ; H from Si to Ge to Sn and slight increase in ; H from Sn to Pb is the consequence of poor shielding effect of intervening d and f-orbitals and increase in size of the atom.
(c) Metallic Character Metallic character increases down to the group C (non-metal) SI, Ge (metalloid) Sn, Pb (metals).
(d) Oxidation States The group 14 elements have four electrons in the outermost shell. The common oxidation states exhibited by these elements are +4 and +2. Carbon also exhibits negative oxidation states. Since, the sum of the first four ionisation enthalpies is very high, compounds in +4 oxidation states are generally covalent in nature. In heavier members the tendence to show +2 oxidation state increases in the Ge(e) Nature of Halides The elements can form halides of formula MX2 and MX4 (where, X=F, Cl, Br, I). Except carbon all other members react directly with halogen under suitable condition to make halides.
Most of MX4 are covalent with sp3 hybridisation and tetrahedral in structure. Exceptions are SnF4 and PbF4 which are ionic nature. Heavier members Ge to Pd are able to make halides of formula MX2. Stability of halides increases down the group.
