polarizability/nucleophiles

[Sacci Mohan]

I do not understand why Br is a stronger nucleophile than F- in terms of polarizability. Can someone explain this please?

[Kimberly Wagas 1H]

Stronger nucleophiles have higher polarizability. Br has a greater atomic radius compared to F, so the distance between its electrons and nuclear charge is greater. The greater the distance of electrons from nuclear charge, the less control the nuclear charge has on the charge distribution, and thus the increased polarizability of the atom. Therefore, Br has higher polarizability. Another factor that influences polarizability is the number of electrons. The greater the number of electrons, the less control the nuclear charge has on charge distribution, and thus the increased polarizability of the atom.

[Hayley Hammons 1L]

Br is a larger molecule than F-, giving it a larger atomic radius and a larger bonding region where the valence electrons are further away from the nucleus, allowing for easier polarization. This ease in polarization increases the likelihood that the valence electrons can be used to form a sigma bond with an electrophile, making Br a better nucleophile than F-.