why bond angles of the chalcogens go on decreasing down the group? the charge density decreases and so the angle should increase as initially lp-lp repulsion was dominant but later bp-bp repulsion takes the lead...

All the members form volatile hydrides of the type AH₃. All hydrides are pyramidal in shape. The bond angle decreases on moving down the group due to decrease in bond pair–bond pair repulsion.

The decreasing order of basic strength of hydrides is as follows :

NH₃> PH₃AsH₃> SbH₃> BiH₃.

The increasing order of boiling points is as follows :

PH₃< AsH₃< NH₃< SbH₃.

NH₃is thermally most stable andBiH₃is least stable. This is because inNH₃, N – H covalent bond is the strongest due to small size of N atom. Hence, the decomposition temperature ofNH₃will be the highest.The increasing order of reducing character is as follows,NH₃< PH₃AsH₃< SbH₃< BiH₃.

Thank You

Ruchi

Askiitians faculty