4.4 Intermolecular forces

Question 1

What characteristics do intermolecular forces determine?

Answer 1

1. Solubility
2. Volatility (evaporation at normal temp)
3. Conductivity
4. Boiling/melting points

Question 2

Types of intermolecular forces

Answer 2

1. London dispersion forces
2. Dipole-dipole
3. Hydrigen bonding

Question 3

Explain London (dispersion) forces

Answer 3

LONDON: betwen opposite ends of temporary poles of two molecules

• non-polar molecule
• strength increases with molar mass
• temporary/instantaneus dipole forms (e density shifts - induced dipole)

London - weak - answer why non-polar gases are gases in room temp (Cl₂, O₂, CH₄)

Also exist in polar molecules but not reconginsed because they have stronger intermol. forces

Question 4

Explain dipole-dipole attraction

Answer 4

DIPOLE-DIPOLE:

• polar molecules (permanent poles)
• electrostatic attraction
• strength increases with molar mass, strength depends on distance between poles

Question 5

Explain van der Waal’s forces

Answer 5

Includes: London, dipole-dipole and dipole-induced forces

Can occur in one molecules between different side chains - proteins

Question 6

Explain induced-dipole forces

Answer 6

INDUCED-DIPOLE: when a polar molecule induces a dipole in a non-polar molecule - shift of e

Question 7

Explain hydrogen bonding

Answer 7

HYDROGEN BONDING:

• polar molecules - F/O/N with H
• influence physical properties
• the strongest intermolecular

e shift towards F/O/N - H high attraction of e - lone pairs

H bonds a=can also be within a molecule - DNA

Question 8

Wich trend does hydrogen bonding disrupt?

Answer 8

Boiling temperatures increases down the group but hydrigen bonding disrups the trend in F/O/N

Question 9

Bonding in ice

Answer 9

Water molecules in ice are arranged in tetrahedrals - 4 H bonds by each molecule - less dense tan liquid because distance due to arrangement is kept => less dense so the same number of molecules take up larger volume - water anomaly

Question 11

Relative strength of intermolecular forces

Answer 11

Hydrogen > dipole-dipole > induced-dipole > London

Question 12

Compare volatility, solubility in water, solubility in hexane and electrical conductivity in ionic/polar covalent/on-polar covalent/iant covalent compounds

Answer 12