Is the H-F Bond Polar?

Given

• Pauling electronegativity of fluorine: 3.98

• Pauling electronegativity of hydrogen: 2.20

• Bond-type guidelines: delta EN < 0.4 nonpolar; 0.4-1.7 polar; > 1.7 ionic (approximate)

Find

Whether the H-F bond is nonpolar covalent, polar covalent, or ionic, and the partial-charge assignment.

Principle

Electronegativity measures how strongly an atom pulls shared electrons toward itself. The difference between two bonded atoms predicts the bond type: small differences mean electrons are shared nearly equally (nonpolar), large differences mean the pull is so one-sided the electron effectively transfers (ionic), and the middle ground gives a polar covalent bond with partial charges.

Formula

Solution

1. Compute the difference: delta EN = 3.98 - 2.20 = 1.78.

2. Compare with guidelines: 1.78 falls in the polar covalent range (it is a borderline, strongly polar case).

3. The more electronegative atom pulls electrons toward itself: fluorine carries the partial negative charge (F delta-).

4. Hydrogen is left electron-poor and carries the partial positive charge (H delta+).

5. Answer: polar covalent bond, written H(delta+) - F(delta-).

Unit check

Electronegativity is a dimensionless index, so their difference is dimensionless too — it can only feed into a classification rule, never a physical quantity. The partial charges are fractions of an electron, dimensionless as well.

What this means physically

The pull toward fluorine gives HF one of the largest bond dipoles of any diatomic molecule, which is why hydrogen fluoride forms unusually strong hydrogen bonds and attacks glass. A single subtraction on the Pauling scale predicts real, dramatic chemistry.