Phosphorous have valence electrons in the 3rd energy level. It also have the 3d sublevel.
P 1s²2s²2p⁶3s²3p³3d⁰ → P* 1s²2s²2p⁶3s¹3p³3d¹
When the electron occupies the 3d sublevel, valence of phosphorus can be equal to five.
Nitrogen have valence electrons in the 2rd energy level. At the nitrogen atom, the 3d sublevel is absent.
