List all possible molecular geometries (shapes) for a nonpolar molecule with the formula AX₄. A)tetrahedral B)see-saw C)square planar D)either tetrahedral or square planar E)any of the above shapes

Question

Quizplus · Accepted Answer

The formula AX₄ indicates that the central atom (A) has one lone pair of electrons (S1) and is bonded to one other atom (X) and 14 other atoms (B) which are presumably all identical. This general formula corresponds to the AX15 parent structure. According to VSEPR theory, this parent structure has a geometry that depends on the total number of electron pairs, which is defined as the sum of the number of bonded atoms and lone pairs of electrons around the central atom. In this case, the total number of electron pairs is 16. Since the molecule has a lone pair of electrons, the actual geometry will be distorted from the ideal geometry. The possible geometries for an AX3E molecular structure (where E is a lone pair of electrons, but the number of B atoms remains the same) are trigonal planar and bent (or V-shaped), depending on the magnitude of the lone pair-bonding pair repulsion. However, as the number of B atoms increases, the possible geometries expand, and the molecule can adopt a range of geometries from tetrahedral (AX4E1) to square planar (AX4E2) to see-saw (AX4E1U1) and even T-shaped (AX3E2). However, due to the large number of bonded atoms, the lone pair-bonding pair repulsions may be strong enough to distort the preferred square planar geometry to a tetrahedral geometry, in which the lone pair is directed opposite to the X-A-X axis. Therefore, the best choice for the possible molecular geometry of this molecule is either tetrahedral or square planar.

List All Possible Molecular Geometries (Shapes) for a Nonpolar Molecule