[6.3] intermolecular forces

Question 1

where are intermolecular forces found?

Answer 1

• between molecules of simple covalent substances (eg. methane, water, iodine)
• not giant structures (eg. ionic, giant covalent, metallic)

Question 2

what are the 3 types of intermolecular forces?

Answer 2

• london forces (weak)
• permanent dipole-dipole interactions (medium)
• hydrogen bonds (strong)

Question 3

where are london forces found?

Answer 3

in all molecules (polar and non-polar)

Question 4

what can london forces also be called?

Answer 4

• dispersion forces
• induced dipole-dipole interactions

Question 5

describe how london forces arise [3]

Answer 5

• uneven distribution of electrons
• causes an instantaneous dipole
• causes induced dipoles in neighbouring molecules

Question 6

what 2 factors affect the strength of a london force?

Answer 6

• the number of the electrons
• the shape of a molecule

Question 7

how does the number of electrons affect the strength of a london force?

Answer 7

• the greater the number of electrons a molecule has, the stronger the instantaneous dipoles
• the greater the induced dipole-dipole interactions
• stronger attractive forces

Question 8

how does the shape of a molecule affect the strength of a london force?

Answer 8

• the points of contain between molecules also affects the strength of the london forces
  > straight chain molecules have greater points of contact so stronger london forces
  > branched chain molecules have fewer points of contact so weaker london forces

Question 9

where are permanent dipole-dipole interactions found?

Answer 9

in polar molecules only

Question 10

what do simple molecules form in solid state?

Answer 10

in the solid state, simple molecules form a regular structure called a simple molecular lattice

Question 11

what is the solubility of polar and non-polar substances?

Answer 11

• like dissolves like
  > polar molecules will only dissolve in polar solvent
  > non-polar substances will only dissolve in non-polar solvents

Question 12

what is required for a solute to dissolve?

Answer 12

• the solute particles must be separated from each other and surrounded by the solvent particles
• the forces of attraction between solute and solvent particles must be strong enough to overcome the solute-solute and the solvent-solvent attractions
  > non-polar substances cannot dissolve in polar solvents because the intermolecular forces cannot be broken