Here's why:
* Nitrogen's valence electrons: Nitrogen has 5 valence electrons.
* Hydrogen's valence electrons: Each hydrogen atom has 1 valence electron.
* Total valence electrons: 5 (N) + 3 (H) = 8 valence electrons.
* Bonding: Nitrogen forms three single bonds with the three hydrogen atoms, using up 6 valence electrons.
* Lone pair: This leaves 2 valence electrons on the nitrogen atom, which form a lone pair.
You can visualize this with a Lewis structure:
H
|
H - N - H
|
H
The two dots on the nitrogen represent the lone pair.
