Nitrogen has a unique property in that it has three different types of orbitals: s, p and d. Two of these orbitals are degenerate (p) and the third orbital is non-degenerate (s). This means that the electron density will be equal in all three orbitals.
In methane (CH4), there are only two carbon atoms and so each carbon atom contributes one p orbital to the molecule. This means that there is one unpaired electron for each carbon atom.
In ammonia (NH3), there are three nitrogen atoms and so each nitrogen atom contributes one s orbital to the molecule. There are no p orbitals because all of them have been filled by electrons from the other two atoms. The two unpaired electrons come from two nitrogen atoms, which each have an s orbital with an unpaired electron.
Last modified: September 20, 2022