INTERMOLECULAR FORCES
In the solid and liquid phases, there is a force of attraction between
molecules to keep them together, known as intermolecular forces
The type of IMF and strength of IMF determine the phase as well
as the physical properties of a substance at a particular
temperature and pressure
Van der Waals Forces
Dipole-dipole forces
Attractive electrostatic forces between permanent dipoles
The negative side of one molecule attracts the positive side of an
adjacent molecule
The oppositely charged sides of polar molecules align towards
each other
The stronger the dipoles, the greater the attractive force
London dispersion forces
Involves attraction between non-polar molecules or atoms
Continuous motion of electrons surrounding an atom or molecule
may cause an uneven or asymmetrical distribution of elections
Therefore, one side of the atom or molecule contains more
electrons than the other, producing a temporary dipole
One dipole then induces another dipole in a neighbouring molecule
A weak attractive force develops between the induced dipoles
Hydrogen Bonds
Special dipole-dipole force between polar molecules containing an
H atom covalently bonded to an N,O or F atom
N,O and F atoms are small and have a large electronegativity and
very strong dipole forms- strongest IMF
Small molecules allow atoms to move closer together
IMF vs Inter-atomic forces
There are 3 types of inter-atomic bonds:
1. Covalent
2. Ionic
3. Metallic
Forces between atoms or ions and are strong
In the solid and liquid phases, there is a force of attraction between
molecules to keep them together, known as intermolecular forces
The type of IMF and strength of IMF determine the phase as well
as the physical properties of a substance at a particular
temperature and pressure
Van der Waals Forces
Dipole-dipole forces
Attractive electrostatic forces between permanent dipoles
The negative side of one molecule attracts the positive side of an
adjacent molecule
The oppositely charged sides of polar molecules align towards
each other
The stronger the dipoles, the greater the attractive force
London dispersion forces
Involves attraction between non-polar molecules or atoms
Continuous motion of electrons surrounding an atom or molecule
may cause an uneven or asymmetrical distribution of elections
Therefore, one side of the atom or molecule contains more
electrons than the other, producing a temporary dipole
One dipole then induces another dipole in a neighbouring molecule
A weak attractive force develops between the induced dipoles
Hydrogen Bonds
Special dipole-dipole force between polar molecules containing an
H atom covalently bonded to an N,O or F atom
N,O and F atoms are small and have a large electronegativity and
very strong dipole forms- strongest IMF
Small molecules allow atoms to move closer together
IMF vs Inter-atomic forces
There are 3 types of inter-atomic bonds:
1. Covalent
2. Ionic
3. Metallic
Forces between atoms or ions and are strong
