FC10 Intermolecular forces

Question 1

What are the 3 main categories of intermolecular forces

Answer 1

• Induced dipole-dipole interactions (London forces)
• Permanent dipole-dipole interactions
• Hydrogen bonding

Question 2

What is the strongest intermolecular forces

Answer 2

Hydrogen bonding

Question 3

Do London forces exist between polar or non-polar molecules

Answer 3

Both

Question 4

How are induced dipole-dipole forces created

Answer 4

• Movement of electrons produces a changing dipole in a molecule
• This instantaneous dipole induces a dipole on a neighbouring molecule
• This induced dipole induces further dipoles on neighbouring molecules

Question 5

Are London forces stronger in molecules with more electrons or less electrons

Answer 5

More electrons

Question 6

Do permanent dipole-dipole interactions act between polar or non-polar molecule

Answer 6

Polar molecules

Question 7

Explain why simple molecular compounds have low melting and boiling points

Answer 7

Weak intermolecular forces are broken by the energy present at low temperatures

Question 8

Explain why simple molecular compounds do not usually dissolve readily in water

Answer 8

There is little interaction between the molecules in the lattice and the polar solvent molecules

Question 9

Explain why simple molecular compounds have poor electrical conductivity

Answer 9

There are no mobile charged particles

Question 10

What is a hydrogen bond

Answer 10

A special type of permanent dipole-dipole interaction found between molecules containing H-O, H-N, H-F

Question 11

How do you draw/ show a hydrogen bond

Answer 11

dotted/ dashed line

Question 12

What are the anomalous properties caused by hydrogen bonding

Answer 12

• The solid (ice) is less dense than the liquid (water)
• The relatively high melting and boiling points

Question 13

Why is ice less dense than water

Answer 13

• Hydrogen bonds hold water molecules apart in an open lattice structure
• The water molecules in ice are further apart than in water
• Solid ice is less dense than liquid water so floats

Question 14

How many hydrogen bonds can one molecule of water form, and where will they form

Answer 14

4 bonds
- 2 on the 2 hydrogen atoms
- 2 of the 2 lone pairs of electrons on the oxygen

Question 15

Why does water have a relatively high melting and boiling point

Answer 15

• Hydrogen bonds are extra forces, over and above the London forces
• Hydrogen bonds require a vast amount of energy to break, far more energy than just London forces
• So it has a much higher melting and boiling point than expected

Question 16

State which of the following have hydrogen bonding, H20, H2S, CH4, CH3OH, NO2

Answer 16

• H20
• CH3OH