Final answer:
According to VSEPR theory, if there are three electron domains in the valence shell of an atom, they will be arranged in a trigonal planar geometry.
Step-by-step explanation:
According to VSEPR theory, if there are three electron domains in the valence shell of an atom, they will be arranged in a trigonal planar geometry. A molecule with three electron groups orients the groups as far apart as possible, forming an equilateral triangle with angles 120° apart. An example of a molecule with a trigonal planar geometry is BF3.