5: Intermolecular forces

Question 1

How do induced dipoles form?

Answer 1

• Fast-moving electrons in clouds
• Fluctuations in electron density
• Move to one side
• Cause instantaneous dipole
• This induces a dipole in the neighbouring molecule

Question 2

What factors increase the strength of an induced dipole and why?

Answer 2

• A larger molecule (has a larger cloud)

- A greater SA (has a more exposed electron cloud)

Question 3

What are permanent dipole dipole interactions?

Answer 3

Weak electrostatic forces of attraction between molecules caused by the slight positive and slight negative charges on polar molecules

Question 4

‘Permanent dipole dipole interactions take places instead of induced dipole dipole interactions.’ True or false?

Answer 4

FALSE; permanent dipole dipole interactions take place IN ADDITION to induced dipole dipole interactions

Question 5

Which elements can have hydrogen bonds? (3)

Answer 5

F, N, O

Question 6

The bond between hydrogen and an electronegative element is very polarised. What happens because of this?

Answer 6

Because it’s so polarised, a weak bond forms between the hydrogen and the lone pair on the electronegative element

Question 7

What are two physical properties of molecules containing hydrogen bonding?

Answer 7

• More soluble in water

- Higher melting and boiling point