Account for the following observations : (i) AlCl_(3) is a lewis acid. (ii) Though fluorine is more electronegative than chlorine yet BF_(3) is a weaker Lewis acid than BCl_(3). (iii) PbO_(2)is stronger oxidising agent than SnO_(2).(iv) The +1 oxidation state of thallium is more stable than its +3 state.

Account for the following observations : (i) AlCl_(3) is a lewis acid.

1.	Account for the following observations : (i) AlCl_(3) is a lewis acid. (ii) Though fluorine is more electronegative than chlorine yet BF_(3) is a weaker Lewis acid than BCl_(3). (iii) PbO_(2)is stronger oxidising agent than SnO_(2).(iv) The +1 oxidation state of thallium is more stable than its +3 state.
Answer» Solution :(i) The `Al` atoms in `AlCl_(3)`, has only six electron in tis valence shell and hence can accept apair of its octet. Therefore, it actsas a Lewis acid. (II) The B atom in `BF_(3)` or has only six electronsin the valene shell and hence can accept a pair of electrons to COMPLETE its octet. Therefore,both `BF_(3)` and`BCl_(3)` act asLewis acids.But in `BF_(3)`,the SIZE of empty 2p-orbital on Band 2p-orbital on F containingthe lone pair of electronsof F is donated to the empty 2p-orbital to a considerable EXTENT and hence electrondeficiency of B decreases. In contrast,in `BCl_(3)`, the size of `3p`-orbital of Cl containing the lone pair . of electron is muchbigger than the empty 2p-orbital of B and hence donation of lone pairof electron of Cl to B does notoccur to any significantextent. Thereforeelectron deficiency of B is much higherin `BCl_(3)` than thatis `BF_(3)`and hence `BCl_(3)` is a stronger LEWISACID than `BF_(3)`. (iii) N/A, (iv) N/A