Effect of Lone Pairs on Polarity

[Danielle Sumilang - 1F]

Hello!

I understand that symmetry and electronegativity influence polarity but I was wondering how lone pairs affect whether or not a molecule is polar. Thank you!

[Chem_Mod]

It would depend. Lone pairs are electron-dense. They take up space and force other nearby functional groups to be repelled. In the case of NH₃, a lone pair forces the molecule to take a trigonal pyramidal shape. The bond angle thus changes to be less than 109.5 degrees, even though we would expect 109.5 degrees due to its tetrahedral electron pair geometry. The lone pair makes it this way. However, there are times when lone pairs may allow the molecule to be nonpolar, as the case of XeCl₂. The molecular geometry of XeCl₂ is linear with symmetric electron region distribution. Therefore this molecule is nonpolar.