Account for the following : (i) Ammonia is more basic than phosphine. (ii) Elements of Group - 16 generally show lower value of first ionisation enthalpy compared to the elements in the corresponding periods of Group - 15. (iii) Electron pair gain enthalpy with (-)ve sign for fluorine is less than that for chlorine.

Account for the following : (i) Ammonia is more basic than phosphine.

1.	Account for the following : (i) Ammonia is more basic than phosphine. (ii) Elements of Group - 16 generally show lower value of first ionisation enthalpy compared to the elements in the corresponding periods of Group - 15. (iii) Electron pair gain enthalpy with (-)ve sign for fluorine is less than that for chlorine.
Answer» <P> Solution :Ammonia is more basic than `PH_(3)` : This is becuase of small size of NITROGEN, electron pairs are crowded in a small REGION and more available, whereas in `PH_(3)`, the electrons are more diffused due to large size of phosphorus hence less available. (ii) Elements of group - 16 generally show LOWER value of first ionisation enthalpy as COMPARED to the elements in corresponding periods of group - 15. This is because group - 15 members have `ns^(2)np^(3)` configuration, due to half filled p - orbital, they are more stable , hence greater ionisation enthalpy. (iii) Electron pair gain enthalpy with negative sign high for fluorine is less than that of chlorine : When an extra electron is added to fluorine repulsion occurs and energy released is less or electron gain enthalpy is less negative in comparison to chlorine, which is due to small size of 2p orbital of fluorine in comparison to 3p orbital of chlorine.