How can you explain higher stability of BCl_(3) as compared to TlCl_(3

1.	How can you explain higher stability of BCl_(3) as compared to TlCl_(3) ?
Answer» SOLUTION :In the excited STATE, boron has three unpaired electrons in its valence shell which enter into covalent bond formation with three Cl atoms (e.g., Fig.) and FORM `BCl_3` molecule. In this COMPOUND, boron atom exhibits +3 oxidation state and is `sp^2` hybridised. The molecule is partly stabilised by `P pi-P pi` back bonding. On the other hand, due to inert pair effect, the `6s^2` ELECTRON pair in TI remains reluctant in bond formation. This is why the +1 oxidation state of TI is more stable than the +3 state. Hence, `TICI_3` formed in the +3 state is not much stable. Therefore, BCl3 is more stable as compared to `TICI_3`.

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