Question

What is the bond polarity of CH4?

Answer 1

The dipole moment of a `"C-H"` bond is probably 0.34 D.

Explanation:

We often say that a `"C-H"` bond is nonpolar because the electronegativities of `"C"` and `"H"` are so close to each other.

However, the values are `"C = 2.55"` and `"H = 2.20"`.

The difference corresponds to 3% ionic character, so a `"C-H"` bond should have a small dipole moment.

From experimental IR intensities of methane, we can infer that `µ_text(C-H) = "0.34 D"`, directed `stackrelcolor(blue)(δ⁻)("C")"-"stackrelcolor(blue)(δ⁺)("H")`.

Theoretical calculations give varying results, but most experimental values are between 0.3 D and 0.4 D.