Which compound has bond angles nearest to 120
? (a) o=c=s b CHI3C H2C=O d H-C=C-H e CH4
The Correct Answer and Explanation is:
Correct Answer: (c) H₂C=O (formaldehyde)
Formaldehyde (H₂C=O) exhibits bond angles that are closest to 120° because of the trigonal planar geometry around the central carbon atom. The carbon atom in H₂C=O is sp² hybridized, which means its three hybrid orbitals arrange themselves in a planar triangular shape to minimize electron repulsion, resulting in bond angles of approximately 120°.
The molecule consists of a central carbon atom double bonded to an oxygen atom and single bonded to two hydrogen atoms. The sp² hybridization of the central carbon leads to three electron domains (two C–H bonds and one C=O bond) lying in a plane, arranged as far apart as possible. This results in idealized bond angles of 120°, though small deviations may occur due to the presence of the more electronegative oxygen atom influencing electron distribution.
Analyzing the other options:
- (a) O=C=S (carbonyl sulfide): This is a linear molecule with a bond angle of approximately 180°, due to sp hybridization of the carbon atom.
- (b) CHI₃ (triiodomethane): The carbon in CHI₃ is sp³ hybridized, forming a tetrahedral geometry with bond angles around 109.5°.
- (d) H–C≡C–H (ethyne): Each carbon atom is sp hybridized, resulting in a linear geometry with bond angles of 180°.
- (e) CH₄ (methane): The carbon atom is sp³ hybridized, producing tetrahedral geometry and bond angles close to 109.5°.
Only H₂C=O shows geometry where bond angles are near 120°, characteristic of molecules with sp² hybridization and trigonal planar shape. This makes it the most suitable answer among the given options.
