Question

(a) What conditions must be met if a molecule with polar bonds is nonpolar? (b) What geometries will give nonpolar molecules for \(\mathrm{AB}_{2}, \mathrm{AB}_{3}\), and \(\mathrm{AB}_{4}\) geometries?

Short answer

For a molecule with polar bonds to be nonpolar, it must have a symmetrical geometry, ensuring the bond dipoles cancel each other out, resulting in a net molecular dipole moment of zero. For \(\mathrm{AB}_{2}\), \(\mathrm{AB}_{3}\), and \(\mathrm{AB}_{4}\) geometries, the nonpolar geometries are linear, trigonal planar, and tetrahedral, respectively, as the bond dipoles cancel out in these configurations.

Step-by-step solution

(Conditions for nonpolar molecules)

In order for a molecule with polar bonds to be nonpolar, the molecule must have a symmetrical geometry, with its polar bonds being arranged in such a way that their dipoles cancel each other out. This means that the molecule has a net molecular dipole moment of zero.

(Nonpolar geometries for \(\mathrm{AB}_{2}\))

In the case of \(\mathrm{AB}_{2}\) geometries, the only nonpolar geometry is linear. When \(\mathrm{AB}_{2}\) is linear, the bond dipoles are opposite to each other and cancel out, resulting in a nonpolar molecule.

(Nonpolar geometries for \(\mathrm{AB}_{3}\))

For \(\mathrm{AB}_{3}\) geometries, the nonpolar geometry is trigonal planar. In this geometry, the bond dipoles of the three polar bonds are symmetrically distributed in a plane, and as a result, they cancel each other out. This results in a nonpolar molecule.

(Nonpolar geometries for \(\mathrm{AB}_{4}\))

In the case of \(\mathrm{AB}_{4}\) geometries, the nonpolar geometry is tetrahedral. In the tetrahedral geometry, the bond dipoles of the four polar bonds are symmetrically distributed in space, resulting in their dipoles canceling each other out. This leads to a nonpolar molecule.