The structure of NH₃ can be explained with the help of sp³ hybridization; according to electronic configuration of nitrogen how many unpaired and lone pair electrons are present

According to valence shell configuration of nitrogen in the ground state is 2s² 2p¹_x2p¹_y2p¹_z having three unpaired electrons in the sp₃ hybrid orbitals and a lone pairs of electrons is present in the fourth one. These three hybrid orbitals overlap with 1s orbitals of hydrogen atoms to form three N-H sigma bonds.