Why are the following molecular formulas impossible(a) CH5 (b) C2H7

Key points

Octet rule

Group 1A–7A elements react to achieve an outer shell of eight valence electrons.

Stable octet form 

It is from where an atom, or ion has an outer shell filled with electrons. In fact, it's a form where the p orbital is completely filled with all six electrons. Stable octet form corresponds to ground state electron configuration of  noble gasses.

Step 1 of 3

We have to explain why these two molecular formulas are not possible.

(a)        (b)

Group 1A–7A elements react to achieve an outer shell of eight valence electrons and this is known as octet rule..