Intermolecular Forces Flashcards
What are intermolecular forces? (1 mark)
⦾ Forces between molecules (1)
What are the 3 types of IMFs? (3 marks)
- VWFs (induced dipole-dipole) (1)
- Permanent dipole-dipole (1)
- Hydrogen (1)
What are Van der Waals forces? (1 mark)
⦾ Cause all atoms + molecules to be attracted to each other (1)
Explain how Van der Waals forces are created? (8 marks)
⦾ e- in charge clouds move v. fast (1)
⦾ any moment, more likely to be one side (1)
⦾ (creates) temporary dipole (1)
⦾ causes another temporary dipole in opposite direction on neighbouring atom (1)
⦾ 2 dipoles attracted (1)
⦾ Continues (chain reaction) (1)
⦾ Dipoles created + destroyed all the time (1)
⦾ Overall atoms attracted to each other (1)
Explain (fully) the forces that hold iodine molecules together? (4 marks)
⦾ Iodine atoms in molecule held in pairs via strong covalent bonds (1)
⦾ molecules held in molecular lattice arrangement (1)
⦾ via weak VWFs (1)
⦾ crystal stucture (1)
What are the factors that affect Van der Waals forces strength? How? (4 marks)
⦾ Bigger molecules have bigger electron clouds - stronger VWFs (2)
⦾ Molecule shape - long + straight lie closer than branched - stronger VWFs between (2)
What happens to VWFs when you boil a liquid? (2 marks)
⦾ need to overcome IMFs (1)
⦾ so particles escape liquid surface (1)
Explain why liquids with stronger VWFs have higher boiling points? (1 mark)
⦾ More energy needed to overcome stronger VWFs (1)
What other properties can VWFs affect? (2 marks)
⦾ Melting point (1)
⦾ Viscosity (1)
What is the trend in strength of VWFs and boiling points down the noble gases? (3 marks)
⦾ no. of e- increase (1)
⦾ VWFs increase (1)
⦾ bp. increases (1)
What is the trend in VWFs and boiling points as alkane chains get longer? (4 marks)
⦾ no. of e- increase (1)
⦾ area over which VWFs can act increases (1)
⦾ therefore stronger (1)
⦾ bp. increases (1)
What are permanent dipole-dipole forces? (2 marks)
⦾ weak electrostatic forces of attraction (1)
⦾ between 𝛿+ and 𝛿− charges on neighbouring molecules (1)
What would happens when an electrostatically charged rod is placed next to a jet of polar liquid? e.g. water
(1 mark)
⦾ Liquid moves towards rod (1)
Explain how the liquid is able to move towards the electrostatically charged rod? (1 mark)
⦾ Polar liquids contain molecules with permanent-dipoles (1)
Explain why it doesn’t matter if the rod is +vely or -vely charged as to why the polar liquid is still able to move? (2 marks)
⦾ Polar molecules in liquid turn around (1)
⦾ (so) oppositely charged end attracted to rod (1)
What effect does increased polarity of the liquid have on the attraction between the rod and the jet? (2 marks)
⦾ Stronger electrostatic attraction between rod + jet (1)
⦾ greater deflection (1)
What is the effect on non-polar liquids when placed near charged rod? (1 mark)
⦾ no effect (1)
What is Hydrogen bonding? (1 mark)
⦾ When H covalently bonded to F, N or O (1)
How do F, N and O bond with hydrogen? (2 marks)
⦾ V. electronegative (1)
⦾ draw bonding e- away from H atom (1)
Explain how Hydrogen bonding works? (3 marks)
⦾ Polarised bond (1)
⦾ H’s v. small so v. high charge density (1)
⦾ forms weak bonds with lone e- pairs on F, N or O (1)
Explain how hydrogen bonding works in water?
2 marks
⦾ H bonding between (1)
⦾ 𝛿+H and lone e- pair on 𝛿−O (1)
Explain how hydrogen bonding works in ammonia?
2 marks
⦾ H bonding between (1)
⦾ 𝛿+H and lone e- pair on 𝛿−N (1)
State and explain the effect of hydrogen bonding on properties of substances? (3 marks)
⦾ Higher mp.s/bp.s (1)
⦾ (because) extra energy needed (1)
⦾ (to) break H bonds (1)
What is an unusual property of water? (1 mark)
⦾ Ice less dense than liquid water (1)
Explain the effect of hydrogen bonding when liquid water cools to form ice? (4 marks)
⦾ Molecules make more H bonds (1)
⦾ arrange themsleves into regular lattice structure (1)
⦾ increased distance between molecules as ice compared to liquid (due to H bonding) (1)
⦾ (therefore) ice less dense than water (1)
What are the 3 physical properties of simple covalent compounds? (3 marks)
- Electrical conductivity (1)
- Melting point (1)
- Solubility (1)
Explain the 3 physical properties of simple covalent compounds? (6 marks)
Electrical conductivity:
⦾ don’t conduct electricity (1)
⦾ (because) no free ions or e- to carry charge (1)
Melting point:
⦾ Low mp.s (1)
⦾ (because) weak forces between molecules easily broken (1)
Solubility:
⦾ Some dissolve in water (1)
⦾ (depending) on how polarised molecules are (1)
What is the main factor that determines the melting/boiling point of a substance?
⦾ Strength of induced dipole-dipoleforces
What are the 2 main factors that affect the overall strength of intermolecular forces:
⦾ Down group 7 hydrides from HCl to HI?
(4 marks)
⦾ Polarity of molecules decreases (1)
⦾ (so) strength of permanent dipole-dipole interactions decrease (1)
⦾ No. of e- increases in molecule (1)
⦾ (so) strength of induced dipole-dipole interactions increases (1)
How are the boiling points affected:
⦾ Down group 7 hydrides from HCl to HI?
(3 marks)
⦾ Increases (1)
⦾ Increased strength of induced dipole-dipole interactions (1)
⦾ (has) greater effect on bp. than decreasing strength of permanent dipole-dipole interactions (1)
What is the strength of induced dipole-dipole interactions for 2 molecules with similar number of electrons? (1 mark)
⦾ Similar (1)
Which group 7 hydride has the highest boiling point?
1 mark
⦾ HF (1)
