Which of the following best explains why the two C–O bond lengths in the formate ion,

CHEMISTRY · Single correct · A Level · Chemistry · Bonding · Bonding

Problem

\mathrm{HCO}_{2}^{-}

, are identical and intermediate between a typical C=O double bond and a C–O single bond? (a) Each

\text{C–O}

bond alternates between single and double character because the bonds rapidly switch positions in time. (b) Because the carbon atom is

\text{sp}^2

-hybridized, both

\text{C–O}

bonds must have identical lengths regardless of bond order. (c) Electron delocalization produces a resonance hybrid in which each

\text{C–O}

bond has a fractional bond order between 1 and 2. (d) Steric repulsion between the two oxygen atoms forces the

\text{C–O}

bonds to adopt identical lengths.