Final answer:
In formaldehyde, the central carbon atom is surrounded by three electron groups, leading to a trigonal planar shape with a bond angle of approximately 120°, slightly adjusted due to the C-O double bond to about 121° and 118° for the H-C-H bonds.
Step-by-step explanation:
The approximate H-C-O bond angle in formaldehyde (H₂C=O) is about 120°. The central carbon atom in formaldehyde has three electron groups surrounding it because the double bond counts as one electron group. These electron groups repel each other and adopt a trigonal planar shape, which typically has 120° bond angles. However, the presence of the C-O double bond creates a slight deviation from this ideal angle, causing a little larger bond angle adjacent to the double bond and slightly smaller angles between the single bonds. Therefore, the exact bond angles in formaldehyde are about 121° for the C=O bond and 118° for the H-C-H bonds.