Intermolecular Forces

Question 1

Intermolecular forces

Answer 1

The force of attraction & repulsion between molecules
Simply referred to as van der waals forces

4 types of van der waals forces
Dipole-dipole
London dispersion force
Hydrogen bonding
Ion-dipole force

These attractions between particles determine the physical properties of substances and include the boiling point, freezing point, vapour pressure, and compressibility

Question 2

Dipole-Dipole Forces

Answer 2

A force of attraction between polar molecules

The permanency of the dipoles in the neighboring molecules adds to the strength of the force and also the magnitude of the dipole moments

The force of attraction increases significantly between molecules as the distance decreases

Like dissolves like - polar solutes dissolve in polar solvents and non-polar solutes dissolve in non-polar solvents.

Question 3

London Dispersion Forces

Answer 3

The simultaneous attraction of the electrons of one molecule by the positive nuclei in the surrounding molecule (ie. instantaneous dipoles)

It is the weakest force of attraction between particles and it is due to the instantaneous dipole-induced-dipole attraction.

London dispersion forces are the ONLY force of attraction between non-polar molecules. The noble gases also exhibit London forces of attraction.

Question 4

Using Vander Waals forces to predict Boiling Points

Answer 4

The more polar a molecule is, the higher the boiling point

The greater the number of electrons (ie. increase in molecular weight), the stronger the London dispersion force and therefore, higher boiling point

Isoelectric (same # of electrons) molecules have the same London Dispersion force

Question 5

Hydrogen Bonding

Answer 5

The attraction of hydrogen bonded to FON, to another FON attached to hydrogen

GREATER # OF HYDROGEN BONDING (to itself) = STRONGER INTERMOLECULAR FORCE (IMF)

Question 6

Ion-Dipole Forces

Answer 6

In this type of force of attraction, an ion is attracted to its oppositely partially charged area of a polar molecule
The size and charge of the ion and the magnitude of the dipole moment of the polar molecule are factors in the strength of the ion-dipole force