TeXes Science Practice Test

Which pair of atoms is known to form a nonpolar covalent bond?

1. O-Na

2. N-O

3. H-H

4. C-O

The correct answer is: H-H

A nonpolar covalent bond occurs when two atoms share a pair of electrons equally. This is typically found in situations where the two atoms involved are of the same element or have very similar electronegativities. The pair of hydrogen atoms (H-H), as found in the diatomic hydrogen molecule, exemplifies this because both hydrogen atoms have identical electronegativities, which leads to the equal sharing of the bonding electrons. In contrast, the other pairs involve elements with differing electronegativities. For instance, sodium (Na) is a metal and has a much lower electronegativity compared to oxygen (O), leading to an ionic bond rather than a covalent bond. Nitrogen (N) and oxygen (O) also have differing electronegativities, which results in a polar covalent bond. Lastly, carbon (C) and oxygen (O) can form polar covalent bonds due to their difference in electronegativity as well. Hence, the hydrogen pair is the only one that forms a truly nonpolar covalent bond.