What is the bond polarity of CH4?

1 Answer
May 8, 2018

Answer:

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")#.

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