1.5- Intermolecular Forces

Question 1

What are van der Waals’?

Answer 1

The attraction between the instantaneous and induced dipoles in neighbouring molecules

Question 2

Describe how instantaneous and induced dipoles occur

Answer 2

When two electrons approach each other, the electrons in one molecule repel the electrons in the other causing an uneven distribution of charge

Question 3

Describe the trend in the amount of energy needed to break van der Waals’ forces

Answer 3

Molecules with more electrons/ more mass have larger dipoles therefore experience greater van der Waals’ forces .
The shape of the molecules, increasing the fit between molecules increases the amount of contact between electrons

Question 4

Define the term permanent Dipole-Dipole attractions

Answer 4

The attraction between the positive end of the permanent dipole on a molecule with the negative end of the permanent dipole of a neighbouring molecule

Question 5

Define the term hydrogen bonding

Answer 5

The attraction between the lone pair of electrons on a very electronegative atom ( Nitrogen Oxygen and Fluorine ) in one molecule and a hydrogen atom in a neighbouring molecule in which the hydrogen atom is covalently bonded to a very electronegative atom

Question 6

Describe why the boiling point of water is much higher than expected

Answer 6

Hydrogen bonds require a very high amount of energy to break in comparison with other dipole dipole attractions

Question 7

Describe why the boiling point of water is much higher than expected

Answer 7

Hydrogen bonds require a very high amount of energy to break in comparison with other dipole dipole attractions

Question 8

Describe how the density of water changes in a liquid to a solid

Answer 8

When water freezes it expands, this is because the water molecules move away from one another in order to maximise the hydrogen binding in its structure.

Ice has an open lattice with hydrogen bonds holding the water molecules apart.
When the ice melts these rigid hydrogen bonds collapse