Question 26.SE.1: Formaldehyde has the Lewis structure Describe how the bonds ...
Formaldehyde has the Lewis structure
Describe how the bonds in formaldehyde are formed in terms of overlap of appropriate hybridized and unhybridized orbitals.
Analyse We are given a structure containing several types of bonds and are asked to interpret these bonds in terms of hybrid orbitals.
Plan Single bonds are of the σ type, whereas double bonds consist of one σ-bond and one π-bond. The ways in which these bonds form can be deduced from the geometry of the molecule, which we predict using the VSEPR model.
Solve The C atom has three electron domains around it, which suggests a trigonal planar geometry with bond angles of about 120°. This geometry implies sp² hybrid orbitals on C.
These hybrids are used to make the two C—H and one C—O σ-bonds to C. There remains an unhybridized 2p orbital on carbon, perpendicular to the plane of the three sp² hybrids.
The O atom also has three electron domains around it, so we assume that it has sp² hybridization as well. One of these hybrids participates in the C—O σ-bond, while the other two hybrids hold the two non-bonding electron pairs of the O atom. Like the C atom, therefore, the O atom has an unhybridized 2p orbital that is perpendicular to the plane of the molecule. The unhybridized 2p orbitals on the C and O atoms overlap to form a C—O π-bond, as illustrated in Figure 26.7.
