Two different compounds have the formula $X e F_{2} C l_{2}$ $XeF_2Cl_2$ . How do you write the Lewis structures for these two compounds, and describe how measurement of dipole moments might be used to distinguish between them?

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Answer 1 · 2016-12-04T01:11:26

Here's how I would do it.

Draw the Lewis structure.

Start with a trial structure. Put two $F$ $"F"$ atoms and two $Cl$ $"Cl"$ atoms on a central $Xe$ $"Xe"$ , and give every atom an octet.

Trial

The trial structure has 32 valence electrons.

$1 Xe + 2 F + 2 Cl = 8 + 14 + 14 = 36$ $"1 Xe" + "2 F" + "2 Cl" = 8 + 14 + 14 = 36$ valence electrons

We have four extra electrons, so we add 2 lone pairs on the central atom.

The Lewis structure is

XeF2Cl2

This is an ${AX}_{4} E_{2}$ $"AX"_4"E"_2$ system.

Its electron geometry is octahedral.

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The bulky lone pairs will occupy the top and bottom axial positions, and the $F$ $"F"$ and $Cl$ $"Cl"$ atoms will occupy the equatorial positions.

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The molecular geometry is square planar.

The atoms can arrange themselves in two ways.

In the trans isomer the $F—Xe—F$ $"F—Xe—F"$ and $Cl—Xe—Cl$ $"Cl—Xe—Cl"$ bond angles are 180 °.

Trans

The $Xe—F$ $"Xe—F"$ bond dipoles (red) cancel, and the $Xe—Cl$ $"Xe—Cl"$ bond dipoles cancel.

There is no net dipole, so the trans isomer is nonpolar.

In the cis isomer the $Xe—F$ $"Xe—F"$ and $Xe—Cl$ $"Xe—Cl"$ bond dipoles do not cancel.

Cis

The cis isomer has a net dipole moment and the molecule is polar.

Two different compounds have the formula XeF2Cl2XeF_2Cl_2. How do you write the Lewis structures for these two compounds, and describe how measurement of dipole moments might be used to distinguish between them?