Unit 4. Intermolecular Forces

Question 1

What are intermolecular bonds

Answer 1

the bonds within the molecule

Question 2

What are intermolecular forces

Answer 2

forces that exist between molecules

Question 3

What are intermolecular forces responsible for

Answer 3

physical properties such as the boiling point, melting point and solubility of a substance

Question 4

Name the intermolecular forces

Answer 4

London dispersion forces, dipole–dipole forces and hydrogen bonding. Note that London dispersion forces and dipole–dipole forces are collectively known as van der Waals forces.

Question 5

explain London dispersion forces

Answer 5

the weakest type of intermolecular force
exist between all atoms and molecules
consist of temporary or instantaneous dipoles and induced dipoles, caused by changes in electron density within an atom or molecule.

Randomly electrons may be concentrated on one side of an atom or molecule, giving this side a slight negative charge, and the opposite side a slight positive charge.

These opposite charges are given the symbols δ+, (for a partial positive charge) and δ- (for a partial negative charge).
A molecule with a temporary dipole can induce a dipole in a neighbouring molecule; this is known as an induced dipole

Question 6

What determines the straight of London dispersion forces

Answer 6

The ease with which the electrons in an atom or molecule form a temporary or induced dipole (their polarisability).

The surface area of the molecule.

Question 7

What affects Polarisability

Answer 7

The increase of the molar mass of a molecule also increases its polarisabillity

Question 8

What effect do London dispersions forces have

Answer 8

Increased boiling point, especially as molar mass increases due to an increase in polarisabillity

Question 9

When do dipole dipole forces occur

Answer 9

Dipole–dipole forces (or attractions) only exist between polar molecules that have a permanent dipole.

this permanent dipole arises due to the difference in electronegativity

Question 10

When does hydrogen bonding occur

Answer 10

between molecules that have an electronegative nitrogen, oxygen or fluorine atom directly bonded to a hydrogen atom.

Question 11

What are the effects of hydrogen bonding

Answer 11

Higher boiling points

Question 12

What IMF do non polar molecules have

Answer 12

London dispersion forces