question_answer 1)

  Arrange the elements N, P, O and S in the order of: (i) increasing first ionisation enthalpy. (ii) increasing non-metallic character

Answer:

  (i) The first ionisation enthalpy of S is less than that of P as S has unsymmetrical configuration and P has symmetrical configuration. P and N belong to the same group. The atomic radius of P is more than N and thus, first ionisation enthalpy of P is less than N. O and N belong to same period having atomic numbers 8 and 7 respectively. O has unsymmetric structure while N has stable symmetrical configuration as each p-orbital is half filled. Hence, the ionisation enthalpy of O is less than N. (ii) Non-metallic character increases in a period and decreases in a group. Thus, the order is: P < S < N < O.