Intermolecular Forces Worksheet
Fill in the Blank:
Terms: bonds, charges, dipole, forces, dipole-dipole forces, hydrogen bonding, ions, ionic, London
dispersion forces, unchanged, unequal
1. When a molecular substance changes state (ex: from liquid to gas), the atoms within the molecules are
unchanged
2. No bonds
are broken when a molecular substance changes state.
3. The forces holding
ions
together in
ionic
solids are ionic electrostatic forces. Opposite charges
attract each other. These are the strongest intra-particle
forces
.
4. The strongest intermolecular forces in a sample of oxygen gas are the London Dispersion Forces
5. Unequal sharing of electrons in a molecule results in the formation of partial charges on the
molecule.
6. A dipole occurs because one part of a molecule has a partial positive charge while another part of a
molecule has a partial negative charge.
There are 3 intermolecular forces present in a sample of water. List the 3 intermolecular forces in order of
strength from strongest to weakest:
1. ____Hydrogen Bonding__________
2. ____Dipole-Dipole Forces________
3. ____London Dispersion Forces____
Diagrams
Draw a diagram showing how 5 water molecules would interact in the liquid state:
Draw a diagram showing how water molecules would interact in the gas state:
Explain, using intermolecular forces, what has happened when the sample of water has changed from a
liquid to a gas.
Energy provided from heat causes the water molecules to move faster, gaining kinetic energy, shich
means that the individual molecules of water are able to move away from each other and break the
hydrogen bonding forces between the molecules.
Written Response:
Methane (CH4) and water have the similar molecular masses. Why is methane a gas at room temperature
while water is a liquid at room temperature? Explain, using bonding and intermolecular forces, the
difference between these two molecules.
Methane is a non-polar molecule because it has a symmetrical shape. The only forces present in methane
are London Dispersion Forces.
Water is a polar molecule because it is a bent non-symmetrical molecule with polar covalent bonds. The
strongest force holding the water molecules close to each other is Hydrogen Bonding.
The intermolecular forces in water are much stronger than those in methane. These forces keep water in the
liquid state at room temperature because the water molecules are kept closer together by hydrogen bonding.
Find the boiling points of H2O and H2S in the Chemistry reference books. Explain the difference in boiling
points using intermolecular forces. Be sure to draw out the shapes of the molecules and look at the polarity
of the bonds.
Boiling Points:
H2O
100°C
H2S
-60°C
Both water and H2S have a bent shape, which is non-symmetrical.
But the H-S bond has a _EN = 0.5 while
the H-O bond has a _EN = 1.4
The H-O bond is much more polar thatn the H-S bond
In a sample of H2S there are weak dipole-dipole forces present, but a sample of H2O there are strong
Hydrogen bonding forces present. This explains why water is a liquid at room temperature and H2S is a
gas.