Which hybridization best characterizes the O atom involved in ethanal (acetaldehyde; C2H4O) molecule?
a. sp b. sp2 c. sp3 d. sp3
The correct answer and explanation is:
The correct answer is b. sp2.
In ethanal (acetaldehyde, C2H4O), the oxygen atom is part of a carbonyl group (-C=O), which is characterized by a double bond between carbon and oxygen. The hybridization of the oxygen atom in this case is sp2.
Here is an explanation:
- Structure of ethanal: Ethanale has a simple structure where the central atom, carbon, is bonded to a hydrogen atom and an -CH3 group (methyl group). The oxygen atom is part of the carbonyl group, where it forms a double bond with the carbon atom (C=O).
- Bonding and hybridization: Oxygen in the carbonyl group has one sigma bond with carbon and one pi bond. The carbonyl carbon (C=O) is sp2 hybridized due to its involvement in a double bond, and the oxygen atom must match the carbon’s hybridization. In sp2 hybridization, the oxygen uses three orbitals to form sigma bonds and a lone pair of electrons. This leaves one unhybridized p orbital to form the pi bond with the carbon atom.
- Geometry and bond angles: The sp2 hybridization leads to a trigonal planar geometry around the oxygen atom. The bond angles are approximately 120 degrees, typical of sp2 hybridized atoms. This is consistent with the bond geometry observed in the carbonyl group.
- Lone pairs: The oxygen in ethanal has one lone pair of electrons, which is part of the sp2 hybridization. These lone pairs influence the shape of the molecule and its reactivity but do not interfere with the sp2 hybridization of the oxygen atom.
In summary, the oxygen in ethanal is sp2 hybridized because of its involvement in a double bond with carbon, which results in a trigonal planar structure.