Intermolecular Forces

Question 1

What does intermolecular mean?

Answer 1

Between forces

Question 2

What are intermolecular forces?

Answer 2

• Occur due to constant random movements of electrons within atom shells in molecules
• Not involving any sharing or transfer of electrons
• Two main types of intermolecular force are hydrogen bonding and van der Waals’ forces

Question 3

What is the relative strength of ionic and covalent bonds?

Answer 3

1000

Question 4

What is the relative strength of hydrogen bonds?

Answer 4

50

Question 5

What is the relative strength of permanent dipole-dipole bonds?

Answer 5

10

Question 6

What is the relative strength of London forces?

Answer 6

1

Question 7

What are the different types of van der Waals forces?

Answer 7

• Dipole-dipole interactions (including permanent dipole-induced interactions and permanent dipole-permanent dipole interactions)
• London (dispersion) forces (also known as induced dipole-dipole interactions

Question 8

What are permanent dipole-induced dipole interactions?

Answer 8

• Occur due to present polar bonds
• Molecule with permanent-dipole induce dipole in other molecule

Question 9

What does it mean if a molecule has a permanent dipole?

Answer 9

It has slightly negative and slightly positive ends

Question 10

What happens when permanent-dipole molecules are near other non-polar molecules?

Answer 10

Causes electrons in shells in nearby molecule to shift slightly, causing non-polar molecule to become slightly polar and attraction occurs

Question 11

What are permament dipole-permanent interactions?

Answer 11

• Molecules with permanent dipoles also attracted to other molecules with permanent dipoles
• Usually referred to as permanent dipole-dipole forces as both involve at least one permanent dipole

Question 12

What are London (dispersion) forces?

Answer 12

• Non-polar molecules may be attracted to one another, but forces are very weak
• Instantaneous dipole induces dipole in neighbouring molecules, inducing further dipoles on neighbouring molecules
• Small induced dipoles attract one another, causing weak intermolecular forces

Question 13

What causes London forces?

Answer 13

• Constant random electron movements in atoms’ shells, unbalancing distribution of charge within electron shells, so at any moment, there will be instantaneous dipole across molecule

Question 14

How do London forces change in size?

Answer 14

Increases with increasing electron numbers, so greater electron numbers, larger induced dipoles and greater attractive forces between molecules

Question 15

How do London forces affect boiling points?

Answer 15

In event of non-polar molecules, there are only London forces to be overcome as these forces are so weak, such substances have very low boiling points

Question 16

How do electron numbers affect van der Waals and London forces?

Answer 16

As electron numbers increase, strength of van der Waals’ forces increase and would be London forces as no dipoles are present in any molecules before interacting