What causes the H-F bond polarity?

• A. Electrons are shared equally.
• B. Electrons are pulled toward F because its more electronegative. Thus, the molecule is polar.
• C. Electrons are donated to form ions.
• D. F is less electronegative than H.

Answer: (B)

Polarity in a covalent bond comes from differences in electronegativity between the two atoms. In H–F, fluorine is much more electronegative than hydrogen, so the shared electrons are pulled closer to fluorine. This creates a partial negative charge on fluorine and a partial positive charge on hydrogen, giving the bond a dipole moment and making the molecule polar. Fluorine’s electronegativity is about 4.0 while hydrogen’s is about 2.1, which explains the strong pull. The idea that electrons are shared equally would yield a nonpolar bond, which isn’t the case here. Donating electrons to form ions would describe an ionic bond, not this covalent one. And fluorine is not less electronegative than hydrogen; it’s more, which is why the bond becomes polar.