Intermolecular Forces

Question 1

What are the 3 types of intermolecular forces?

Answer 1

• Hydrogen
• Permanent dipole-dipole
• Induced dipole-dipole

Question 2

When is a molecule non-polar?

Answer 2

Molecule is symmetrical, dipoles cancel out

Question 3

When is a molecule polar?

Answer 3

Molecule is not symmetrical, dipoles don’t cancel out

Question 4

How do you know if simple molecules have hydrogen bonding between them?

Answer 4

• Lone pair of electrons on the F, O or N
• H bonded to an N, O or F

Question 5

Explain how an induced dipole-dipole intermolecular force is formed between 2 non-polar molecules? (5)

Answer 5

• Random movement of electrons in one molecule leads to an…
• Uneven distribution of electrons, creating a…
• Temporary dipole in one molecule
• This induces a dipole in a neighbouring molecule
• Dipoles attract

Question 6

If the strongest intermolecular force is hydrogen bonding, which other forces do they also have?

Answer 6

• Permanent dipole-dipole
• Induced dipole-dipole

Question 7

What increases the strength of induced dipole-dipole forces? (2)

Answer 7

• More electrons
• More surface contact area

Question 8

Which has a higher boiling point, Cl2 or Br2?

Answer 8

Br2 - Has more electrons so stronger induced dipole-dipole forces

Question 9

Why does HBr have a higher boiling point than HCl? (3)

Answer 9

• Both polar molecules
• Strongest intermolecular force is permanent dipole-dipoles
• HBr has more electrons than HCl so stronger induced dipole-dipole forces

Question 10

How does permanent dipole-dipoles arise?

Answer 10

• Difference in electronegativity leads to bond polarity
• There’s an attraction between partially positive on one molecule and partially negative on another

Question 11

SHAPES
Explain how lone pairs of electrons influence the shapes and bond angles?

Answer 11

• Lone pairs repel more than bonding pairs
• This decreases the bond angles