Three pairs of compounds are given below. Identify that compound in each of the pairs which have group 13 element in more stable oxidation state. Give a reason for your choice. State the nature of bonding also.
(i) TlCl3, TlCl
(ii) AlCl3 ,AlCl
(iii) InCl3 ,InCl
(i) Thallium, with electronic configuration of [Xe]4f145d106s26p1 and has both +1 and+3 oxidation state. +1 oxidation state is more dominant but +3 oxidation sate is highly oxidising in nature. The stability of +1 oxidation state increases for heavy element, therefore TlCl will be more stable than TlCl3.
Al < Ga < In < Tl
(ii) In aluminium, the sum of the first 3 ionisation enthalpy decreases, thus aluminium form Al3+. Also, there are No d and f orbital in aluminium which cause poor shielding and responsible for inert pair effect (an effect which shows oxidation state reduce by 2, whichis more stable than other oxidation states). Therefore AlCl3 is more stable than AlCl.
(iii)Indium with electronic configuration [Kr]4d105s25p1and has both +1 and +3 oxidation state. Due to inert pair effect(an effect which shows oxidation state reduce by 2, which is more stable than other oxidation states), in heavy elements, the stability of +1 oxidation state increases, therefore, InCl will be more stable than InCl3.
Al < Ga < In < Tl