Final answer:
In the formate ion, both the carbon and oxygen atoms possess pπ orbitals, which participate in the formation of a pi bond within the C=O double bond.
Step-by-step explanation:
In the formate ion (HCO2−), the atoms that have pπ orbitals are carbon and oxygen. These pi orbitals are involved in the formation of pi (π) bonds, which are a type of covalent chemical bond formed by the overlap of atomic orbitals allowing the sharing of electron density. In the formate ion, the central carbon atom is sp2 hybridized and the oxygen atoms also have sp2 hybrid orbitals.
Correspondingly, one of the oxygen atoms forms a double bond with the carbon atom, which consists of one sigma (σ) bond and one pi (π) bond. The sigma bond is made from the overlap of sp2 orbitals, while the pi bond is made from the side-to-side overlap of unhybridized p orbitals. The electrostatic potential map shows the bond polarity and indicates the red region where the lone pair of electrons are located in two sp2 orbitals.