Question

What is the bond polarity of h2s?

Answer 1

The short version: Sulfur is more electronegative than hydrogen, so the `"H-S"` bond is polar with electron density higher on the sulfur atom.

Explanation:

This leads to `"H"_2"S"` being a polar molecule.

However, the difference in polarity between `"H"` and `"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 `"C-H"` bond is viewed as non-polar and so, therefore, should the `"H-S"` bond.

However, there is some polar character to a `"C-H"` bond.

Its dipole moment is only 0.3 D.

We should therefore expect an `"H-S"` bond to have about the same dipole moment.

Yet, the measured molecular dipole moment of `"H"_2"S"` is 0.95 D.

If this were due entirely to the polar `"S-H"` bonds, the `"S-H"` bond dipole would be at most 0.6 D, with the negative end pointing to the `"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.