S1.1Structure 1 — Models of the particulate nature of matter

Introduction to the particulate nature of matter — IB Chemistry SL Revision Notes & Topical Questions

15 min read 27 parts Lesson 1 of 6 1 quiz

📚 IB Chemistry SL Hub / Topical Revision

0%read

Lesson summary

S1.1 Introduction to the particulate nature of matter — IB CHEMISTRY SL notes: Distinguish elements, compounds and mixtures, choose methods to separate mixtures, and explain states, changes of state and temperature in terms of particles.FeatureElementCompoundMixtureCompositionOne…

Compound properties
Mixture components
Homogeneous mixture
Heterogeneous mixture
Filtration
Fine solids

Part 1 of 11Elements, compounds and mixtures

Feature	Element	Compound	Mixture
Composition	One kind of atom	Two or more elements chemically bonded in a fixed ratio	Substances in no fixed ratio
Separation	Cannot be broken down chemically	Only by chemical reactions	By physical methods
Properties	Characteristic of the element	Different from the constituent elements	Components keep their own properties
Examples	Cu, O₂, S₈	H₂O, NaCl	Air, brine, alloys

Elements, compounds and mixtures

Compound properties

Compound properties sodium chloride differs from reactive sodium and toxic chlorine.

Mixture components

Mixture components are interspersed but not chemically combined, e.g. nitrogen and oxygen in air.

Homogeneous mixture

Homogeneous mixture has uniform composition and properties with one phase, e.g. air, solutions and bronze.

Heterogeneous mixture

Heterogeneous mixture has non-uniform composition,
- and separate components or phases can often be seen, e.g. concrete, orange juice with pulp and sand in water.

Part 2 of 11Choosing a separation method

Principle
- every method exploits a difference in a physical property such as boiling point, solubility, magnetism or density.

Technique	Separates	Property exploited
Solvation (dissolving)	Soluble from insoluble solid, e.g. salt from sand	Solubility in a chosen solvent
Filtration	Insoluble solid from liquid	Particle size
Crystallisation	Dissolved solid from solution	Solubility falls on cooling or evaporation
Recrystallisation	Impure solid purified	Solubility in hot and cold solvent
Simple distillation	Solvent from solution	Large boiling point difference
Fractional distillation	Miscible liquids	Small boiling point differences
Paper chromatography	Components of a solution	Solubility in mobile phase and attraction to paper
Magnetic separation	Iron from sulfur	Magnetism

Part 3 of 11Solvation, filtration and crystallisation

1Solvation

Solvation solvent particles surround and attract solute particles, so only the desired component dissolves.
- (hydration in water)

2Filtration

Filtration the filtrate passes through the filter paper and the insoluble residue stays behind.

3Fine solids

Fine solids vacuum (Büchner) filtration under reduced pressure is faster than gravity filtration.
Very small or dense particles — centrifugation collects them at the bottom of the tube.

4Crystallisation steps

Crystallisation steps heat gently to evaporate some solvent, test saturation with a cold glass rod, cool slowly, filter, wash with distilled water and dry on filter paper.

5Do not boil to dryness

Do not boil to dryness crystals fail to form and hydrated salts such as CuSO₄·5H₂O lose water of crystallisation.
Slow cooling — gives larger, purer crystals.

Part 4 of 11Recrystallisation

Purpose
- purifies an impure solid using differences in solubility in hot and cold solvent.

Dissolve the solid in the minimum volume of hot solvent.

Hot-filter to remove any insoluble impurities.

Cool slowly so the product crystallises while soluble impurities stay in solution.

Collect the crystals by Büchner filtration under reduced pressure.

Wash with a little fresh cold solvent.

Dry on filter paper.

Part 5 of 11Distillation

1Simple distillation

Simple distillation separates a solvent from a solute, or a liquid with a much lower boiling point, by evaporation then condensation.

2Steps

Steps heat the solution, the lowest boiling liquid evaporates, vapour condenses in the condenser and the distillate is collected.
Example — water from salt solution.

3Fractional distillation

Fractional distillation separates miscible liquids with similar boiling points using a fractionating column.

4Example

Example ethanol (78 °C) and water (100 °C), heating to 78 °C to collect the ethanol first.
Safety — an electric heater is used with flammable liquids.
Industrial use — crude oil is separated by fractional distillation.

Part 6 of 11Paper chromatography

Draw a pencil baseline near the bottom of the paper, because pencil does not dissolve.

Place small spots of sample on the line.

Suspend the paper in a shallow layer of solvent with the spots above the solvent level.

Let the solvent (mobile phase) rise through the paper (stationary phase) by capillary action.

Dry the paper and observe the chromatogram.

Distance travelled

Distance travelled components more soluble in the solvent travel further.

Adsorption

Adsorption components more strongly attracted to the paper move more slowly.

Part 7 of 11States of matter

Kinetic molecular theory
- explains the states in terms of the energy, arrangement and motion of particles.

Property	Solid	Liquid	Gas
Shape and volume	Fixed shape and volume	Fixed volume, shape of container	Fills any container
Arrangement	Closely packed, regular, ordered	Close but randomly arranged	Widely spaced, random
Motion	Vibrate in fixed positions	Slide past each other	Fast and random
Density	High	Medium	Very low; easily compressed
Particle energy	Lowest	Medium	Highest

Gas pressure
- arises from particles colliding with the container walls.

Part 8 of 11Changes of state

Nature
- physical changes that are reversible and do not alter the chemical identity.

Change	Change of state	Energy
Melting	Solid to liquid	Endothermic
Vaporisation	Liquid to gas	Endothermic
Sublimation	Solid to gas	Endothermic
Freezing	Liquid to solid	Exothermic
Condensation	Gas to liquid	Exothermic
Deposition	Gas to solid	Exothermic

Energy direction

Energy direction energy is absorbed to overcome interparticle attractions and released when particles come closer.

Boiling

Boiling occurs throughout the liquid at the boiling point, when vapour pressure equals external pressure.

Evaporation

Evaporation occurs only at the surface at temperatures below the boiling point.

Pressure effect

Pressure effect lowering external pressure, e.g. at altitude, lowers the boiling point.

Sublimation examples

Sublimation examples iodine, dry ice (CO₂) and naphthalene sublime at atmospheric pressure.

State symbols

(s), (l), (g) and (aq) for aqueous solution.

Part 9 of 11Temperature and average kinetic energy

Temperature

Temperature a measure of the average kinetic energy of particles, and the Kelvin is the SI unit.

Conversion

T/K = t/°C + 273.15, and a change of 1 K equals a change of 1 °C.

Absolute zero

0 K (−273.15 °C), where particles have minimum kinetic energy.

Proportionality

Proportionality average kinetic energy is directly proportional to absolute temperature.

Same temperature

Same temperature all gases have the same average kinetic energy, but lighter particles move faster on average.

Distribution

Distribution at any temperature particles have a range of speeds.

Part 10 of 11Heating curve

Region	Process	Temperature
Solid heating	Particles vibrate more as kinetic energy rises	Increases
Melting	Energy overcomes attractions and raises potential energy	Constant
Liquid heating	Particles move more freely	Increases
Boiling	Energy separates particles completely	Constant
Gas heating	Particles move rapidly with the highest kinetic energy	Increases

Plateaus

Plateaus energy increases potential energy, not kinetic energy.
- (particle spacing)

Boiling plateau

Boiling plateau is longer than the melting plateau because far more energy is needed to separate particles completely.

Cooling

Cooling the reverse occurs, with condensation and freezing releasing energy.

Part 11 of 11More from the specification

1Phase change energetics

Melting and boiling are endothermic transitions where thermal energy is absorbed to overcome intermolecular forces between particles.

2Latent heat and plateau temperature

During phase transitions, supplied heat increases potential energy rather than kinetic energy, so the temperature remains constant.

3Separation using a suitable solvent

Differential solubility enables separating mixtures by dissolving soluble components in a suitable solvent while insoluble residues are filtered.

4Exothermic phase changes

Freezing and condensation release latent heat into the surroundings as intermolecular attractive forces pull particles closer.

5Intermolecular forces

Weak attractions between separate molecules, overcome on melting or boiling.

Key terms

Term	Meaning
Element	A pure substance made of only one type of atom.
Compound	A pure substance of two or more elements chemically combined in a fixed ratio.
Mixture	Two or more substances physically combined in no fixed ratio.
Homogeneous mixture	A mixture with uniform composition and one phase.
Heterogeneous mixture	A mixture with non-uniform composition and distinguishable phases.
Sublimation	The change of state from solid directly to gas.
Absolute zero	0 K, the temperature of minimum particle kinetic energy.

Avoid these mistakes

Saying temperature rises during melting — it stays constant while energy changes potential energy.

Treating a mixture as having a fixed formula — its components are in any proportion and keep their properties.

Writing the neutral scale as °C in gas calculations — absolute temperature in kelvin is needed.

Evaporating a crystallisation solution to dryness — slow cooling of a saturated solution gives crystals.

Last updated: 14 October 2026