Question

Aluminium forms[ alf6]3- but boron does not form [bf6]3- ion . why

Answer 1

aluminium is more electropositive in nature

Answer 2

Explanation:

The atomic number of aluminium is 13 and its electronic configuration is as follows.

          $1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}$

It can be seen that 3p shell of aluminium is not filled and moreover, it has vacant 3d orbital. Therefore, aluminium can expand its octet and it can accommodate 6 fluorine atoms. Hence, aluminium can form $[AlF_{6}]^{3-}$.

Whereas atomic number of boron is 5 and its electronic configuration is as follows.

          $1s^{2}2s^{2}2p^{1}$

Boron does not have any d-orbitals and therefore it cannot expand its valency more than 4. Therefore, it does not form $[BF_{6}]^{3-}$.