Basicity of Group 15 hydrides [duplicate]








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[Why does basicity of group 15 hydrides decrease down the group?](/questions/16215/why-does-basicity-of-group-15-hydrides-decrease-down-the-group)

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Why does the basicity of Group 15 hydrides ($\ce{NH\_3,~ PH\_3,~ etc}$) decreases down the group ? 


I know that's because of its Lewis Base nature due to the lone pair but wouldn't the more EN element be less reluctant to give the lone pair ?  

 And nitrogen is most EN in that group .




It can be explained by the very helpful [Bent's rule](http://en.wikipedia.org/wiki/Bent%27s_rule). As nitrogen is more electronegative than phosphorus, there is a bigger s character of the sp3 hybrid orbitals that are used to form the bond to hydrogen than the ones of phosphorus. As a result, the sp3 hybrid orbital that holds the electron pair, has a bigger p character for nitrogen than for phosphorus, meaning that the pair is more distant from the nucleus and more susceptible to donation.


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