A N sp3 hybrid orbital and a H 1s orbital combine to generate each N-H - sigma bonding orbital, which has two electrons.
What is a sigma bond?
Atomic orbitals and/or hybrid orbitals overlapping along the bond axis to produce a covalent bond known as a sigma bond.
Sigma bonds can form when two overlapping s atomic orbitals, one s orbital and one p orbital, or two p orbitals overlap. This is illustrated in the diagram above. Sigma bonding can also result from the overlap of two hybridized atomic orbitals, such as sp-sp.
The overlapping of atomic orbitals distinguishes sigma and pi bonds from other varieties of covalent connections. Atomic orbitals colliding together create covalent bonds.
In contrast to pi bonds, which are created by the lateral overlapping of two atomic orbitals, sigma bonds are created when atomic orbitals overlap head-to-head.
