Here's why:

* Central atom: Nitrogen (N) is the central atom.

* Valence electrons: Nitrogen has 5 valence electrons.

* Bonds: Nitrogen forms three single bonds with three hydrogen (H) atoms.

* Lone pair: Nitrogen also has one lone pair of electrons.

The lone pair repels the bonding pairs more strongly than the bonding pairs repel each other. This results in the three hydrogen atoms being pushed down, creating a pyramidal shape with the nitrogen atom at the apex.