Negative End
Positive End
Polarity in Molecules
a sidedness or asymmetry
Why is polarity important?

Polarity tells us a lot about the behavior of a
compound.
Why is water a liquid at room temperature?
 Why is oxygen a gas at room temperature?
 Why does table salt dissolve easily in water,
but have a REALLY high melting point?

one!
Polar Bonds
 Polar
Bond
Electronegativity difference creates a pull in
the electrons to one side of bond
 Slightly negative and positive end of bond

Polar Molecule

Polar Molecule




Must contain at least one polar bond
Creates slightly negative and slightly positive end of
a molecule
Forces are not cancelled out.
All forces in molecule can be summed to determine
the molecular polarity.
Deciding if a Molecule is Polar

Need to draw a vector to show polarity

Vectors have magnitude & direction
 A vector is an arrow that represents the
strength of force of something (like a charge),
and the direction in which it is acting.

Vectors of equal strength in opposite
directions cancel out!
Vectors for Dipoles

The vector points in the direction of
the partial negative charge

It has a + on the partial positive end.
+
δ
δ
Molecules with 2 Atoms


Any 2-atom molecule with a polar
bond has a dipole moment.
The molecule will be polar
Molecules with 3+ atoms.
 In
some molecules, the polar bonds will cancel
each other out making the molecule non-polar
(even though it contains polar bonds)
 This is based on the molecule’s geometry
O C O
Other Molecules are Polar
Water
Nitrogen trifluoride
Sulfur tetra fluoride is polar, as well.
Now it is your turn
to determine whether a
molecule is
polar or not!