Two different compounds have the formula #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?

1 Answer
Dec 4, 2016

Answer:

Here's how I would do it.

Explanation:

Draw the Lewis structure.

Start with a trial structure. Put two #"F"# atoms and two #"Cl"# atoms on a central #"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# 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# 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"# and #"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"# and #"Cl—Xe—Cl"# bond angles are 180 °.

Trans

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

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

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

Cis

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