1. IB Chemistry Power Points
Topic 4
Bonding
www.pedagogics.ca
LESSON
Determining Molecule Polarity

2. DEMONSTRATION - POLAR MOLECULES
Evidence place a liquid in a burette
allow it to run out
place a charged rod alongside the stream of liquid
polar molecules are attracted by electrostatic attraction
non-polar molecules will be unaffected
NET DIPOLE - POLAR NON-POLAR

3. Determining Molecular Polarity
We must know if individual covalent bonds are polar
and
the shape of the molecule
Example 1 : nitrogen gas
molecules
containing only
non-polar bonds
ARE NOT POLAR

4. Determining Molecular Polarity
We must know if individual covalent bonds are polar
and
the shape of the molecule
Example 2 : hydrofluoric acid HF
bond dipole

5. Determining Molecular Polarity
We must know if individual covalent bonds are polar
and
the shape of the molecule
Example 2 : hydrofluoric acid HF
molecule dipole
molecule is POLAR

6. Example 3 Methane
C-H bonds slightly polar
but molecule is symmetrical
bond dipoles cancel out
C
molecule is NON-POLAR

7. Example 4 Ammonia
N-H bonds polar
molecule is asymmetrical
lone pair (negative)
hydrogen atoms (positive)
molecule is POLAR

8. Example 5 water

9. POLAR MOLECULES - SUMMARY
Concept s molecules containing non-polar bonds are non-polar
symmetrical polar bonds: the molecule isn’t polar
asymmetrical polar bonds: the molecule will be polar
HYDROGEN CHLORIDE TETRACHLOROMETHANE WATER
NET DIPOLE - POLAR NON-POLAR NET DIPOLE - POLAR
To determine molecular polarity, we must know molecular shape and
bond polarity.