The elements of group 15 have five electrons (two in the s – orbital and three in p – orbital) in their respective valence shells. It is difficult to lose three electrons to form E3+ ions. It is even more difficult to lose all the five valence electron (two – s and three – p) to from E5+ ions. Therefore higher elements have no tendency to form ionic compounds. They prefer to form covalent compounds by sharing of electrons. Thus, elements in the +5 oxidation state are more covalent than in the +3 oxidation state.