Chemical Bonding Worksheets Page 19
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2210.8 ELECTRONEGATIVITY AND POLARITY: Why Oil and Water Don’t Mix
For diatomic molecules:
– nonpolar molecules: when the 2 atoms have equal EN values
– polar molecules: when the 2 atoms have different EN values
– have dipole (+ve and –ve ends)
For molecules of three of more atoms:
– polarity depend on individual bonds and geometry around central atom
– Polar molecules have an overall dipole (positive end and negative end)
– In nonpolar molecules, all the individual dipoles cancel → no overall dipole.
Guidelines for Determining if a Molecule is Polar or Nonpolar
1. Use a dipole arrow to indicate which atom in a nonpolar bond is more electronegative.
2. Determine if there is an overall dipole:
– If two arrows point in opposite directions, all arrows point in, or all arrows point out, then
the dipoles cancel → nonpolar molecule.
– If all arrows point towards the same direction and don’t cancel, there is an overall
dipole for the molecule → polar molecule.
– A dipole moment is the quantitative measure of the separation of charges in a
molecule → The higher the dipole moment, the more polar the molecule.
Example: First determine if there are any polar covalent bonds then if they cancel or if there is
an overall dipole to determine whether the following molecules are polar or nonpolar:
CO
:
H
O:
2
2
H
CCl 4
CHCl 3
CHEM 121 Tro Chapter 10 F2012
page 19 of 22
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