Which substance contains a nonpolar covalent bond?

• A. O2
• B. NaCl
• C. NH3
• D. HBr

Answer: (A)

Nonpolar covalent bonds form when electrons are shared almost equally between atoms, which happens when the bonded atoms have the same or very similar electronegativity. In oxygen gas, the two atoms are identical, so the electrons are pulled about equally and the bond is nonpolar covalent.

The other substances involve either a large difference in electronegativity or a molecular shape that creates an uneven distribution of charge. Sodium chloride forms an ionic bond because sodium donates electrons to chlorine, producing ions rather than a shared electron pair. Ammonia has N–H bonds with a noticeable electronegativity difference, and the molecule’s geometry creates a polar molecule with a net dipole. Hydrogen bromide also has a polar covalent bond due to the H–Br electronegativity difference, giving a dipole moment.