Question

give an example of a molecule with steric number 6 having 3 bond pair and 3 lone pairs.

Answer 1

Dear student,
For steric number 6, the geometry of the molecule is octahedral. Steric number 6 can theoretically have the following combinations:
1) 6 bond pair and 0 lone pair- Perfect octahedral.
2) 5 bond pair and 1 lone pair- Square pyramidal.
3) 4 bond pair and 2 lone pairs- Square planar.
4) 3 bond pair and 3 lone pairs.

This 4th combination is not possible because of following two reasons:
a) Ce​ntral atom having 3 bond pair and 3 lone pairs would mean that the electrons around the central atom are 9. ( 6 from lone pairs and three from bond pairs). This is not possible.
b) The other reason is that a molecule having 3 bond pair and 3 lone pairs will not be stable due to very high lone pair-lone pair repulsions.

So, a molecule with 3 bond pair and 3 lone pairs does not exist.

Regards