Which halogen, bromine or iodine, will form the more polar bond with phosphorus?

1 Answer
Nov 17, 2016

Well, bromine is more electronegative than iodine, and thus a #P-Br# bond should be more polar.


By definition, electronegativity is the ability of an atom involved in a chemical bond to polarize electron density towards itself. There are various scales, of which the Pauling scale is the earliest, and is still widely.

It is well-known that electronegativity increases across a Period (i.e. it increases from left to right as we face the Periodic Table, but decreases down a Group). This makes sense on the basis of atomic structure: as we add protons to a nucleus, the nuclear charge attracts the valence electrons, and demonstrably reduces the atomic radius. On the other hand, when we descend a Group, the valence electrons are farther removed from the nuclear core, and the valence electrons are effectively shielded from the increased nuclear charge.

And thus a #P-Br# bond should be more polar than a #P-I# bond.