Ammonia also has four pairs of electrons around the central atom, but three are
bonding pairs between N and H and the fourth is a lone pair on the nitrogen. The nuclei
form a trigonal pyramid with the three bonding pairs; with the lone pair, they make a nearly
tetrahedral shape. Because each of the three bonding pairs is attracted by two positively
charged nuclei (H and N), these pairs are largely confined to the regions between the H
and N atoms. The lone pair, on the other hand, is concentrated near the nitrogen; it has no
second nucleus to confine it to a small region of space. Consequently, the lone pair tends
to spread out and to occupy more space around the nitrogen than the bonding pairs. As a
result, the H-N-H angles are 106.6", nearly 3" smaller than the angles in methane.