Question #5981b

Carbon tetrachloride, #"CCl"_4#, is a nonpolar molecule because of its molecular geometry.

In order for a molecule to be polar, it must have a net dipole moment. In the case of carbon tetrachloride, that net dipole moment is equal to zero.

Here's why that is the case.

The #"C" -"Cl"# bond is indeed quite polar. Chlorine is more electronegative than carbon, which means that it will attract the bonding electrons more.

Consequently, a partial negative charge, #delta^(-)#, will appear on the chlorine atom and a partial positive charge, #delta^(+)#, will appear on the carbon atom.

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A bond dipole moment will thus appear for each of the four #"C"-"Cl"# bonds that exist in a molecule of carbon tetrachloride. Because these four bonds are identical, theese dipole moments will also be identical in magnitude.

Now, carbon tetrachloride has a tetrahedral molecular geometry. This means that the resultant of any three #"C"-"Cl"# bonds will always

• be equal in magnitude
• have an opposite direction

with the fourth. In other words, no net dipole moment will exist because the four bond dipole moments that arise from the polar #"C"-"Cl"# bonds will cancel each other out.

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