Wed February 20, 2013 By: Shrijeet

Unlike phosphorus, bismuth does not form pentahalide ?

Expert Reply
Thu February 21, 2013

In the case of Bismuth, due to inert pair effect Bi3+ will be much more stable, so it will not form a pentahalide (removal of the s-electrons is necessary for forming the 5+ cation, and due to poor shielding by d and f-orbitals the s-electrons will be very strongly held by the nucleus. The bond formed with two halides will not compensate for the energy required to unpair the s-electrons)

Phosphorus has vancant d-orbitals, and also the s-orbitals are fairly well-shielded from the nucleus. Hence it will more readily form a pentahalide (but note that even phosphorus pentahalides are unstable compared to the respective trihalides).

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