Polar MoleculesSection 4.4

Polar Bonds• Polar Bonds - look up electronegativity

values for each element on the periodic table, then determine the difference:– <0.4 non-polar bond– 0.5-1.7 polar bond– 1.8+ Ionic bond (only if a non-metal and a metal)

Examples• Are the following bonds polar?• HBr BH3

Polar Molecules• Polar Molecules – have polar bonds and the

molecule is not symmetrical (i.e. the charges are not shared equally around the central atom) Use VSPER

• Non-polar molecules – can have polar or non-polar bonds that are equally shared around the central atom.

Empirical Rules for Polar & Non-polar Molecules

Formula Description Example

Polar

ABLinear Molecules

CO, HCl

CxAyBz

Molecules containing C and 2 other types of atoms

C2H5OH

CHCl3

OxAyMolecules with an O at one end

H2O

NxAyMolecules with an N at one end

NH3

Non-polarA2

Diatomic molecules of the same element

O2

CxAyMost carbon compounds

CO2

Examples• NCl3

– Polar

• CO2 –

Non-polar

• H2O–

Polar

Applying VSEPR• Both shape and bond polarity will determine

if the molecule is polar.• If the molecule is symmetrical the molecule

will be non-polar.• A bond dipole is the new way to show the

polar bond (they are vectors…)

A quick review of Vectors

=0

Theoretical Prediction of Molecular Polarity

1. Draw a Lewis Structure

2. Use VSEPR to determine the shape around each central atom

3. Use electronegativities to determine the polarity of each bond.

4. Add the bond dipole vectors and determine if the resultant is 0 (non-polar) or not 0 (polar)

Examples• Are they polar or non-polar molecules?

– SiBr4

– SF2

– BBr3

Today’s Tasks• Pg. 253 #1-3• Pg. 255-256 #6-10 • Pg. 256 #1-3