Chp 7

Question 1

Intermolecular

Answer 1

BETWEEN molecules

Question 2

Intramolecular

Answer 2

IN the molecules

Ionic, covalent, metallic

Question 3

3 types of intermolecular forces?

Answer 3

1. London forces
2. Permanent dipole - dipole interactions
3. Hydrogen bonding

Question 4

Key points for London forces

Answer 4

• exist in anything w electron
• instantaneous dipole makes induced dipole
• more electrons present the stronger LF
• more electrons more likely to be unsymmetrical
• more e- unsymmetrical > larger charge > larger instantaneous + induced dipole

Question 5

Key points for permenant dipole - dipole interactions

Answer 5

• difference in electronegativity
• difference high enough so dipole always present
• sometimes dipole not favourably alligned so they repel
• less significatn than LF when averaged out
• not much effect on physical properties

Question 6

Key points for hydrogen bonding

Answer 6

• Hydrogen must be connected to a more electronegative atom
• Flourine, Oxygen, Nitrogen
• Includes water, alcohol, carboxylic acid
• Bond angle at 180 (linear)

Question 7

Describe alkanes and bonds

Answer 7

• as Mr of alkanes increases the bp increases
• Alkanes only have LF and the more LF present the more energy needed to break them
• Mass increases + more electrons + more instantaneous and induced dipoles + more dipoles means more LF
• Branches alkanes have lower bp as less points of contact which means less LF

Question 8

Describe alcohols and bonding

Answer 8

• contain OH group form hydrogen bonding + LF
• hydrogen bonding increases the bp
• HB has the biggest effect in short chains
• LF biggest effect in longer chains
• Longer chain > more C+H means more LF which overcome HB in OH

Question 9

Enthalpy of vapourisation

Answer 9

Amount of energy to completely seperate molecules of liquid to convert into gas
Measure of strength of intermolecular forces

Question 10

BP of hydrogen halides

Answer 10

HF, HCl, HBr, HI

HF much higher bp > more HB
more electrons means more LF
More energy to break

HF highest then decrease but start to increase

Question 11

H20 + NH3 + HF

Answer 11

H2O + NH3 + HF should have similar BP because similar no. of electrons which means they will have similar LF
water highest (100)
HF (20)
NH3 (-33)

water (1HB)
HF (2HB)
NH3 (4HB)

Question 12

Alcohols + H20

Answer 12

Alcohol form hydrogen bonds with H20
ethanol + h2O mix
solubility of alcohols in water decreases as chain length increases due to LF becoming more predominant

Question 13

Polar molecules solubility

Answer 13

Many polar molecules have limited solubility bcoz either form no HB / not many HB

Question 14

rule for dissolving
like like

Answer 14

NP substance dissolve NP substance
Polar substance dissolve poalr substance