Bond order is defined as

• A. Number of electron pairs in the bond
• B. Total electrons in the molecule
• C. Half the number of electrons shared in a covalent bond
• D. Difference in electronegativity between bonded atoms

Answer: (C)

Bond order tells you how many bonds connect two atoms, i.e., how strong the connection between them is. In covalent bonding, electrons are shared in pairs between the atoms. The bond order is defined as half the number of electrons that are shared between the atoms. So, two shared electrons (one pair) give a bond order of 1; four shared electrons (two pairs) give a bond order of 2; six shared electrons (three pairs) give a bond order of 3. This reflects how many linkages there are between the atoms.

This also explains why the concept can be fractional in some cases: when bonding is delocalized or when considering molecular orbitals, the effective sharing isn’t confined to whole pairs in a single structure, leading to non-integer bond orders.

The other ideas aren’t the definition: the total electrons in the molecule aren’t about the bond strength between a pair of atoms, and electronegativity differences describe polarity rather than how many bonds hold the pair together. While counting electron pairs in a simple single-to-triple bond picture aligns with bond order in straightforward cases, it doesn’t capture partial or delocalized bonding, which the half-the-electrons-shared definition handles cleanly.