Question

VSEPR geometry predicts that the bond angles in formaldehyde (CH2O), a trigonal planar
molecule, will be 120° throughout all three angles. However, analysis showed that the H-C-H
bond angle is slightly smaller at 116.5°, while the two H-C-O angles are slightly larger at
121.8°. Explain this difference in the predicted bond angle vs actual bond angle. ?

Answer 1

VSEPR geometry predicts that the bond angles in formaldehyde (CH2O), a trigonal planar

molecule, will be 120° throughout all three angles. However, analysis showed that the H-C-H

bond angle is slightly smaller at 116.5°, while the two H-C-O angles are slightly larger at

121.8°. Explain this difference in the predicted bond angle vs actual bond angle. ?

Answer 2

• VSEPR (valence shell electron pair repulsion theory) is used to find out the geometry of the compound according to VSEPR theory electronic repulsions between different kinds of electron pairs determine the geometry the combination will try to minimize these electronic repulsions and will adopt A structure in which these bond pairs are as far as possible.

• Suppose, we have a molecule AB2 then the bond pair electrons of bond AB will ripple each other and the molecule will attain a structure in which these are 180 degrees apart from each other.

  Formaldehyde CH2O

  VSEPR geometry: Trigonal planar

  All bond angles = 120degrees

• Only The bond pay religions have been taken into consideration as carbon is joined to the oxygen via a double bond and a double bond Have four electrons in it hence double bond electrons cost more repulsion than single bond repulsion
• due to more repulsion between the double bond and single bond angle theta, one will increase and hence correct bond angles for the compound will be 116.5 degrees

The difference between the predicted bond angle and the actual bond angle.

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