Final answer:
The molecular geometry around the oxygen atom in acetic acid is bent or V-shaped, resembling a trigonal planar geometry with a missing vertex due to two nuclei and two lone pairs, resulting in less than 120° bond angles.
Step-by-step explanation:
The molecular geometry around the oxygen atom in acetic acid is not trigonal planar. In acetic acid, the oxygen atom has two nuclei attached (one to hydrogen and one to carbon) and also possesses two lone pairs. According to the VSEPR theory, this would result in a bent or V-shaped molecular geometry, akin to a trigonal planar arrangement with a missing vertex. The presence of lone pairs causes repulsion that makes the bond angles less than the ideal 120° that is found in a perfect trigonal planar shape.
Specifically, in a dimer form of acetic acid, each oxygen atom participates in two hydrogen bonds, leading to a geometry that is more accurately described as tetrahedral around the oxygen atoms due to the presence of two covalent bonds and two hydrogen bonds.