BONDING CAPACITY OF NITROGEN

The electron configuration of nitrogen ls22s22p3 shows that there are five valence electrons. Three of them are unpaired in this state so nitrogen can form three bonds, however, hybridization still occurs, with the s and p orbitals mixing to form four sp3 hybrid orbitals. 

If nitrogen uses only its p orbitals in bond formation, the angle between N-H bonds would be 90°. However, compounds prefer formations in which electrons are as far apart as possible. For ammonia this is made possible by forming a tetrahedral structure in which the angle between the bonds (M-H) is 107°. This is only possible by undergoing sp3 hybridization. 

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