# What is the bond polarity of h2s?

Dec 24, 2013

The short version: Sulfur is more electronegative than hydrogen, so the $\text{H-S}$ bond is polar with electron density higher on the sulfur atom.

#### Explanation:

This leads to $\text{H"_2"S}$ being a polar molecule.

However, the difference in polarity between $\text{H}$ and $\text{S}$ is very small, so neither the bond nor the molecule are very polar.

The longer version:

The difference in electronegativities of hydrogen (2.20) and sulfur(2.58) is almost exactly the same as that between hydrogen and carbon (2.55).

The $\text{C-H}$ bond is viewed as non-polar and so, therefore, should the $\text{H-S}$ bond.

However, there is some polar character to a $\text{C-H}$ bond.

Its dipole moment is only 0.3 D.

We should therefore expect an $\text{H-S}$ bond to have about the same dipole moment.

Yet, the measured molecular dipole moment of $\text{H"_2"S}$ is 0.95 D.

If this were due entirely to the polar $\text{S-H}$ bonds, the $\text{S-H}$ bond dipole would be at most 0.6 D, with the negative end pointing to the $\text{S}$ atom.

However, hydrogen sulfide has two lone pairs.

(from 2012 Book Archive)

Lone pairs contribute to the molecule's dipole moment even though they do not constitute a 'bond'.

The sulfur 'end' of the lone pair is positive, and the electron 'end' is negative, so one might think of a 'lone pair dipole' contributing to the polarity of the molecule in analogy to a bond dipole.

Thus, it may be the lone pairs that make the major contribution to the polarity of the molecule.