Complete Chemistry for Cambridge IGCSE - Notes

• The book is endorsed by Cambridge International Examinations for the IGCSE Chemistry syllabus 0620.

• The book is divided into two-page units with color coding: Core curriculum (red line), Extended curriculum (white pages with red line), and extra material (colored pages).

• Each chapter ends with a revision checklist and exam-level questions.

• A glossary, past exam papers, interactive tests, revision advice, and sample exam papers are included.

1 States of Matter

1.1 Everything is Made of Particles

• Everything is made of tiny particles that are too small to see.

• In solids, particles are fixed, while in liquids and gases, they move freely.

• Particles in liquids and gases exhibit random motion, colliding and bouncing off each other.

• Random motion: particles move in a zig-zag pattern, changing direction upon collision.

• Evidence for particles includes cooking smells spreading and dust/smoke dancing in sunlight.

• Particles mix via diffusion (collisions) moving from high to low concentration until evenly spread.

• Atoms are the smallest particles that cannot be broken down chemically; some substances are made of single atoms (e.g., argon).

• Molecules consist of two or more atoms joined together (e.g., water, bromine).

• Ions are atoms or groups of atoms carrying a charge (e.g., potassium manganate(VII)).

• Powerful microscopes can "see" particles in solids, such as palladium and carbon atoms.

1.2 Solids, Liquids, and Gases

• Solids have a fixed shape and volume and do not flow.

• Liquids flow easily, have a fixed volume, but take the shape of their container.

• Gases do not have a fixed volume or shape and fill their container.

• Water exists as ice (solid), water (liquid), and steam (gas), changing state with heating or cooling.

• Melting: solid to liquid; freezing: liquid to solid; evaporation: liquid to gas; condensation: gas to liquid.

• Melting point: temperature at which a solid melts (e.g., 0°C for ice).

• Boiling point: temperature at which a liquid boils (e.g., 100°C for water).

• Heating curves show temperature changes during state transitions; melting and boiling points are sharp and clear.

• Nearly all substances can exist as solid, liquid, and gas; melting and boiling points vary widely.

1.3 The Particles in Solids, Liquids, and Gases

• State changes do not alter the particles themselves, only their arrangement.

• Solids: fixed pattern (lattice), strong forces, particles vibrate in place.

• Liquids: particles can move and slide past each other, weaker forces than solids.

• Gases: particles far apart, move quickly, minimal forces.

• Melting: particles gain energy, vibrate more, break away from positions.

• Boiling: particles gain enough energy to overcome forces, forming a gas.

• Evaporation: some particles in a liquid have enough energy to escape as gas even below boiling point.

• The heat required for melting or boiling varies for each substance due to different interparticle forces.

• Changes can be reversed by cooling; gases condense to liquids, and liquids solidify.

• Kinetic particle theory: relates states of matter to particle arrangement and motion

1.4 A Closer Look at Gases

• Gas pressure: results from particles colliding with each other and the container walls.

• Heating a gas in a closed container increases pressure because particles move faster and collide more forcefully.

• Compressing a gas increases pressure because particles are forced into a smaller space, increasing the collision frequency.

• Gases can be compressed into liquids, but liquids and solids cannot be compressed easily.

• Gases diffuse because particles collide and bounce, moving from areas of high to low concentrations.

• Diffusion rate of gases depends on particle mass (relative molecular mass) and temperature.

• Lower mass particles diffuse faster; higher temperature increases diffusion rate.