Determine the hybridization of the central atom in CO2.

• A. sp
• B. sp2
• C. sp3
• D. dsp3

Answer: (A)

Count how many electron-domain regions surround the carbon in CO2. Carbon is bonded to two oxygens by sigma bonds and has no lone pairs, so there are two regions of electron density. Two regions lead to sp hybridization: the s and one p orbital mix to form two equivalent sp hybrids that point in opposite directions, giving a linear molecule. The remaining p orbitals on carbon participate in pi bonding with the oxygens to form the C=O double bonds. Therefore, the central atom is sp hybridized. Choices implying three or four electron domains would predict trigonal planar or tetrahedral geometries, which is inconsistent with CO2's linear structure, and a dsp3 description isn't appropriate for carbon in this simple molecule.