Question

Nitrogen dioxide is a covalent compound. How many oxygen atoms are in a nitrogen dioxide molecule?

Answer 1

In `NO_2`? Well I think you can count them yourself.

Explanation:

`NO_2` is an interesting molecule; because it is a radical species with a formal, lone electron on the central nitrogen:

i.e. `O=N^(+)-O^(-)`

On the central nitrogen, there are FOUR valence electrons, i.e. there is a nitrogen-centred single electron. That there are 4 valence electrons rather than 5 justifies our distribution of a formal positive charge to this site. Because of this single electron, we can rationalize the formation of `N_2O_4`, where the single electrons couple to form a `N-N` bond:

`2NO_2 rarr N_2O_4`

A Lewis structure of `""^(-)O(O=)N^(+)-""^(+)N(=O)O^-` is usually invoked.