Localized Bonding Model for Formaldehyde

The isosurface viewer below illustrates the Valence Bond Theory description of bonding in the formaldehyde molecule. The small red sphere on the right indicates the position of the oxygen nucleus. The gray sphere marks the position of the carbon nucleus. The white spheres on the left mark the positions of the hydrogen nuclei.

Examine each of the atomic orbitals. Identify orbitals for lone pairs of electrons. Identify pairs of orbitals that overlap to form a chemical bond. Compare pairs of overlapping atomic orbitals with the corresponding bonding orbitals for the molecule.

Note that orbital positions are based upon the original view, in which the carbon and oxygen nuclei lie along the z axis. The vertical axis is the x axis.


  1. Why are the oxygen atomic orbitals smaller than the carbon atomic orbitals?
  2. On which atom are the lone pairs located? Which orbitals account for the lone pairs of electrons?
  3. Which atomic orbitals overlap to form the C=O σ bond?
  4. Which atomic orbitals overlap to form the C=O π bond?
  5. How is electron density distributed differently in the C=O σ bond compared with the C=O π bond?
  6. Both the carbon and oxygen atoms have a 2py orbital that is not part of a hybridization scheme. What is the role of the 2py orbitals in bonding in the H2CO molecule?
  7. Which atomic orbitals overlap to form a C-H σ bond?
Carbon Atomic Orbitals:     2py
sp2 hybrid orbitals:     1     2     3

Oxygen Atomic Orbitals:     2py
sp2 hybrid orbitals:     1     2     3

Hydrogen Atomic Orbitals
1s (top)           1s (bottom)

Formaldehyde Orbitals
C-H σ (top)
C-H σ (bottom)
C-O σ
O lone pair (top)
O lone pair (bottom)
C-O π

Formaldehyde Molecule


VB_H2CO.html version 3.0
© Copyright 2015,2020,2023 David N. Blauch