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Bond angle of PH3

Bond angle of PH3

by ankita chaturvedi -
Number of replies: 1

Hello friends,

The bond angle of hydrides of 5th group decreses as:

NH3===107 deg.

it is sp3 hybridised and the presence of a lone pair reduces bond angle by roughly 2 deg.

bond angle of PH3 is===93 deg.

what is the reason of the decrease of the bond angle by such a value despite the fact that PH3 is also sp3 hybridised,

does higher elecronegativity of nitrogen account for this fact??

pls answer my query.

In reply to ankita chaturvedi

Re: Bond angle of PH3

by Ankul Garg -
Well, yes it is the higher electonegativity of N that accounts for this Higher bond angle. Due to greater difference in electronegativities of N and H as compared to that of P and H, the N-H bonds attain a state of instablity due to greater charge separation.
                                               Ndelta(--) --- Hdelta(++)
                                               Pdelta(-) --- Hdelta(+)
To minimise the instability and to minimise the bp-bp repulsion, the N-H bonds tend to be at greatest distance apart, thus contributing to larger bond angle. Also, due to smaller size of N than P, the lone pair of e- is not very far away from Central N atom and thus lp-bp repulsion is minimised. In short, in NH3 the electron density around the central atom is too high which causes the H atoms to align far away from each other so as to minimise the effect of charge separation.
                         N           P
                      /  |  \      /|\