Physical States
of Matter
BIOB111 Session 5

Intermolecular
Forces (IMF)

Intramolecular
Forces

attractive force between two molecules

weak compared to intramolecular forces

high in solids and liquids but negligible in gases

Van Der Waals
Interactions

Dipole-Dipole
Interactions

Hydrogen
Bonds

Solutions

a homogeneous mixture of 2/more substances in which each substance retains its own chemical identity

Components

Solvent

Solute

Solubility
#

Factors
affecting
solubility

Temperature

Pressure

Henry's Law #

Concentration

Polarity

Concentration
of solutions

Percent
concentration

Molar
concentration
(Molarity)

Parts per
million

Dilution

Osmosis

anything with H and O, N, S, F, Cl and a spare pair of electrons

the greater the polarity (related to electronegativity difference) between the partial +ve and partial -ve charge, the greater the strength of the dipole-dipole interaction

occurs in all molecules - only type of intermolecular force present between non-polar molecules

it is the medium in which other present substances dissolve

commonly H2O

the component present in the largest/greatest quantity in the solution

substance that dissolves in the solution

more than 1 solute can be present in one solution

the component present in a lesser amount (lower concentration) relative to the solvent

solubility of solids increases with increasing temperature

gas solubility decreases with increasing temperature (particles move faster, less like to come into contact and mix with other molecules)

has little effect on the solubility of solids and liquids in water

plays a major role in the solubility of gases in water (gases are more soluble at higher pressures)

if any more solute is added to this saturated solution it will not dissolve. It will precipitate.

solubility can be increased in increasing temperature (saturation point becomes higher)

saturated solution contains the maximum amount of solute that can be dissolved in the solvent under given conditions (saturation point)

polar solvents can dissolve polar solutes (e.g. H2O)

non-polar solvents can dissolve non-polar solutes

high pressure = higher solubility

low pressure = lower solubility

at a given temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid

at high partial pressure, more gas molecules dissolve in the liquid (gas particles are more condensed, increased contact between the gas and liquid)

the maximum amount of solute that will dissolve in a given amount of solvent under a specific condition

solubility depends on: temperature, pressure (increase in pressure aids gas dissolving into the solution), concentration, polarity (dissolve best in other polar solvents)

does not alter the number of moles of solute present

C1 x V1 = C2 x V2

the process of adding more solvent (usually water) to a solution in order to lower its concentration

the movement of a solute through a semi-permeable membrane from an area of higher solvent concentration to an area of lower solvent concentration

results from momentary/short-lived uneven electron distributions in molecules

weak temporary intermolecular force that occurs between an atom/molecule (polar or non-polar) and another atom/molecule

dispersion forces, London Forces

partially -ve - more electrons distributed close to it
partially -ve - less electrons close to it
interaction breaks as soon as both atoms/molecules have the same amount of electrons near them

electrostatic attraction between +ve and -ve. The +ve and -ve ends are close to each other

lots of different molecules form the electrostatic attractions, therefore lots of intermolecular bonds

atoms have a difference on partial charge (from a difference in electronegativity)

molecules orient themselves to maximise the +ve ‒ -ve interactions and minimise +ve ‒ +ve and -ve ‒ -ve interactions

occurs between polar covalent molecules

What is required:

  • must have 2/more polar covalent compounds/molecules
  • partial charge difference

H is the least electronegative atom, therefore can have the greatest different in partial charge between two atoms

δ- is due to a lone pair of electrons

H has the greater partial +ve than the other atoms that can be involved

occur between the H δ+ (partial +ve) and the δ- (partial -ve) on another atom of the other molecule

observed among H containing polar covalent molecules where H is covalently bonded to a highly electronegative small elemental atom (O, N, S, F, Cl) (δ-)

dipoles can approach close to each other due to the small size of the H atom

unusually strong dipole-dipole interactions

% of component in total volume of 100%

%v/v or % w/v

the amount of solute in a specified amount of solution

moles/litre

1M solution of NaCl - how much NaCl in 1 mole. Weigh out molar mass in grams. 1M = 58.44g of NaCl dissolved in 1L of water

moles of solute in a solution divided by the litres of the solution

represents 1 part of solute (weight or volume) in 1 million parts of solution (weight or volume)

1ppm = 1g/m3 = 1mg/L = 1μg/mL

true chemical bonds
strong forces within molecules