CAMBRIDGE IGCSE CHEMISTRY BOOK

Particle Theory and States of Matter

Everything is made of particles: All substances, whether solid, liquid, or gas, consist of tiny particles that are not visible to the naked eye. These particles can be atoms, molecules, or ions.
Particle Movement: In solids, the particles are fixed in place and do not move freely. In liquids and gases, however, particles move around randomly and collide with one another.
Random Motion: The movement paths of particles in liquids and gases are random, changing direction upon collision with other particles.
Evidence of Particles: Everyday examples showcase the behavior of particles; for instance:
- Cooking smells spreading suggests gas particles are moving through air.
- Dust and smoke are visible in sunlight due to the particles being bombarded by air particles.

Definition of Diffusion: Diffusion is the process that describes how particles move from areas of high concentration to areas of low concentration until evenly spread.
Types of Particles:
- Some substances consist of single atoms (like argon).
- Many are composed of molecules (like water and gases).
- Others consist of charged groups of atoms known as ions (like potassium manganate).
Visualizing Particles: Advanced microscopes now allow scientists to visualize particles, such as individual palladium and carbon atoms.

Solids: Definite shape and volume due to fixed arrangements of particles in a lattice.
Liquids: Have a defined volume, take the shape of their container, and the particles can slide past one another due to weaker forces than in solids.
Gases: No fixed shape or volume; they expand to fill their container, displaying low density compared to solids and liquids.

Melting and Boiling Points: Water's melting and boiling points are 0°C and 100°C, respectively, indicating the transition between solid (ice), liquid (water), and gas (steam).
**Heat and State Changes:
- Melting: Solid to liquid at its melting point.
- Boiling: Liquid to gas at its boiling point.
- Freezing: Liquid to solid when cooled below 0°C.
- Condensing: Gas to liquid when cooled.

Arrangement of Particles: For substances to change states, their particles rearrange:
- In solids, they vibrate in fixed positions.
- In liquids, they move around each other while maintaining close proximity.
- In gases, they are far apart and move quickly, colliding frequently.

Definition: The kinetic particle theory states that substances can exist in solid, liquid, or gas forms, and their properties vary depending on the arrangement and movement of their particles.
Mass and Energy: Heating increases energy and causes particles in solids to vibrate, leading to melting, and in liquids to become gaseous.

What is Gas Pressure? When gas particles collide with the walls of their container, they exert pressure. This pressure increases with temperature and when a gas is compressed.
Conditions of Gas Behavior: The properties of gases (pressure, volume) can change depending on their temperature and whether they are confined.

Summary of Concepts: Understanding that all matter is made of particles enhances comprehension of how substances interact, change states, and the general principles of chemistry that govern these interactions. Particle behavior is foundational to disciplines such as physics and chemistry.