Final answer:
The bond angle in a trigonal pyramidal molecular geometry, derived from a tetrahedral electron geometry with one lone pair, is approximately 107.3° due to LP-BP repulsions.
Step-by-step explanation:
The student is asking about the bond angle in a molecule with a trigonal pyramidal molecular geometry, which is derived from a tetrahedral electron geometry but has one lone pair. The ideal bond angle for a tetrahedral geometry is 109.5°, but due to the lone pair-bond pair (LP-BP) repulsions, this angle decreases in a trigonal pyramidal structure.
For example, in an ammonia molecule (NH3), which has a trigonal pyramidal shape, the H-N-H bond angles are less than the ideal tetrahedral angle because the lone pair occupies more space and repels the bonding pairs. As a result, the bond angle is approximately 107.3°.