Oxidation state

(i) All exhibit +3 oxidation state and thus complete their octet either by covalent or ionic union.

(ii) Boron being smaller in size cannot lose its valence electrons to form B³⁺ ion and it usually show +3 covalence. The tendency to show +3 covalence however decreases down the group even Al shows +3 covalence in most of its compounds.

(iii) Lower elements also show +1 ionic state e.g Tl ⁺, Ga⁺. This is due to inert pair effect. The phenomenon in which outer shell ‘s’ electrons (ns²) penetrate to (n-1) d-electrons and thus become closer to nucleus and are more effectively pulled the nucleus. This results in less availability of ns² electrons pair for bonding or ns² electron pair becomes inert. The inert pair effect begins after n ³ 4 and increases with increasing value of n.

(iv) The tendency to form M⁺ ion increases down the gp. Ga⁺¹ < Tl⁺¹

Ionization energy

(i) Inspite of the more charge in nucleus and small size, the first ionization energies of this group elements are lesser than the corresponding elements of s block. This is due to the fact that removal of electron from a p-orbitals (being far away from nucleus and thus less effectively held than s-orbitals) is relatively easier than s-orbitals.

(ii) The ionization energy of this group element decrease down the group due to increases in size like other group elements.

(iii) However, ionization energy of Ga are higher than that of Al because of smaller atomic size of Ga due to less effective shielding of 3d electrons in Ga. Thus valence shell exert more effective nuclear charge in Ga to show higher ionisation energies.