Identify the hybridization of the carbon atom in formaldehyde H2CO.
The Correct Answer and Explanation is:
The hybridization of the carbon atom in formaldehyde (H₂CO) is sp².
To understand why this is the case, we begin by analyzing the bonding environment around the carbon atom. Formaldehyde consists of a central carbon atom that forms two single bonds with hydrogen atoms and a double bond with an oxygen atom. This gives the carbon atom a total of three regions of electron density, which include the two sigma bonds to hydrogen and one sigma bond to oxygen (the double bond also includes a pi bond, but the pi bond does not affect hybridization).
When an atom is surrounded by three regions of electron density, it adopts an sp² hybridization. In this model, one s orbital and two p orbitals mix to form three sp² hybrid orbitals, each arranged 120 degrees apart in a trigonal planar geometry. These three sp² orbitals participate in sigma bonding — two with the 1s orbitals of the hydrogen atoms and one with an sp² orbital from oxygen. The remaining unhybridized p orbital on carbon overlaps sideways with a p orbital on oxygen to form the pi bond, completing the double bond between carbon and oxygen.
This arrangement explains both the molecular geometry and bond characteristics of formaldehyde. The trigonal planar shape ensures that the molecule is flat, which aligns with experimental observations of bond angles close to 120 degrees. Moreover, the presence of a delocalized pi system contributes to the reactivity of formaldehyde in various organic reactions, particularly in nucleophilic addition.
Understanding this hybridization is fundamental when analyzing molecular shape, predicting reactivity, and interpreting spectroscopic data. The sp² configuration explains the electron distribution and helps rationalize the planar structure of formaldehyde, which is central to its chemical behavior and biological significance.
