The electronegativity of N (3.0) is higher than that of P (2.1). Due to this N-H bond is more polar than a P-H bond. Also, P and H have the same electronegativity of 2.1 i.e., the P-H bond is non-polar. Therefore, PH₃ does not form hydrogen form.

The structure of NH₃ and PH₃ with their electronegativity is represented below.