Question

A molecule has the formula AX_3, where A is the central atom and each X is bonded to A with a single bond. If there is one unshared pair of electrons around A, then the molecule has a _____ geometry and is non-polar or polar?

A) Trigonal planar, non-polar
B) Trigonal planar, polar
C) Tetrahedral, non-polar
D) Tetrahedral, polar

Answer 1

The AX_3 molecule with one unshared pair of electrons has a tetrahedral electron-pair geometry and a trigonal pyramidal molecular structure, and it is polar.

Step-by-step explanation:

For a molecule with the formula AX_3 and one unshared pair of electrons on the central atom A, there are four regions of electron density (three bonded pairs and one lone pair). This matches the electron-pair geometry known as tetrahedral. However, with one lone pair present, the actual molecular structure becomes trigonal pyramidal rather than tetrahedral. In terms of polarity, the presence of a lone pair of electrons creates an asymmetry in the molecule's shape, leading to an uneven distribution of charge. As a result, the molecule will be polar, making the correct answer (D) Tetrahedral, polar.