In p-Block elements in Gr. 15, we read that as the H-E bond enthalpy decreases, the reducing character of the hydride increases but the acidic character (i.e. basicity) decreses. How could this be? Isn't acidic character given by the ease of fernishing of H atom?
Then in Gr. 16 we read that reducing character as well as acidic character increases down the group as H-E bond enthalpy decreases. This seems suitable. But why is the case not there in Gr. 15?
In case of group 15
Decrease in basic character does not depends on the acidic character and similarly acidic character does not depend on the basic character i.e
Basicity depends on the size and availability of pair of electron on group 15th elements . In basic character case as we move down size of an atom increases and thus electron density on the central atom decreases and availability of electron for donation decreases and basic character also decreases.
Where as acidic character is decided on the basis bond dissociation enthalpy i.e as bond dissociation enthalpy decreases the stability of hydrides decreases. Since bond dissociation enthalpy decreases down the group,it causes a simultaneous decrease in stability of hydrides and thus reducing character of hydrides increases(i.e hydrides become less stable and they easily dissociate to give hydrogen ion). Thus acidic character always increases down the group it never decreases. Similarly it also decreases for 16th group.
Decrease in basic character does not depends on the acidic character and similarly acidic character does not depend on the basic character i.e
Basicity depends on the size and availability of pair of electron on group 15th elements . In basic character case as we move down size of an atom increases and thus electron density on the central atom decreases and availability of electron for donation decreases and basic character also decreases.
Where as acidic character is decided on the basis bond dissociation enthalpy i.e as bond dissociation enthalpy decreases the stability of hydrides decreases. Since bond dissociation enthalpy decreases down the group,it causes a simultaneous decrease in stability of hydrides and thus reducing character of hydrides increases(i.e hydrides become less stable and they easily dissociate to give hydrogen ion). Thus acidic character always increases down the group it never decreases. Similarly it also decreases for 16th group.