Question

Question #5f272

Answer 1

Nitrogen dioxide, or `NO_2`, is an odd-electron molecule, i.e. the number of valence electrons the molecule has is not an even number.

More specifically, nitrogen dioxide has a total of 17 valence electrons - 5 from nitrogen and 6 from each of the two oxygen atoms that comprise the molecule.

Now, VSEPR Theory can be extended to accomodate odd-electron molecules. In this case, the nitrogen dioxide molecule is considered to have a `AX_2E_0.5` geometry, which is right between `AX_2E_0` - linear, and `AX_2E_1` - bent.

http://www.elmhurst.edu/~chm/vchembook/206bent.html

The molecule's geometry will still be closer to bent, but the bond angle will be larger than the ideal `120^@` such a geometry predicts, mostly because the oxygen atoms experience less repulsion from the single electron present on the nitrogen atom.

The actual bond angle for nitrogen dioxide is `134^@`. By comparison, the angle found in the nitrite ion, or `NO_2^(-)`, is `115.4^@`, because now nitrogen has attached a full lone pair of electrons that experience greater repulsion with the oxygen atoms.