Question

Question #44b23

Answer 1

Here's what I get.

Explanation:

The structural formula is:

When you draw the Lewis structure for `"PF"_2"Cl"_3`, you find that it is an AX₅ molecule.

According to VSEPR theory, it must have a trigonal bipyramidal shape.

There are three possible structures:

a) Both `"F"` atoms in the axial position.
b) Both `"F"` atoms in the equatorial locations.
c) One `"F"` axial and one `"F"` equatorial.

Which is most likely to be correct?

The `"Cl"` atoms should be equatorial because

1. The `"Cl"` atoms are bigger than `"F"` atoms, so they are more likely to occupy the equatorial locations (separated by 120° rather than 90°).
2. The `"P-Cl"` σ bonds occupy more space than the `"P-F"` σ bonds because the less electronegative `"Cl"` atoms hold the electrons less tightly. The `"Cl"` atoms will occupy equatorial locations to minimize bond repulsions.

The structure is most likely.

The ball-and-stick model doesn't show correctly the relative sizes of the atoms.

Here's a space-filling picture showing the relative sizes.

An experiment shows that `"PF"_2"Cl"_3` is nonpolar.

The structure shown has no dipole moment:

The two `"P-F"` bond dipoles are at 180°, so they cancel each other. And the three `"P-Cl"` bonds are symmetrically distributed at angles of 120°, so their dipoles also cancel.

Thus, the above structure is correct.