iGCSE Chemistry (Combined) Edexcel

States of Matter

States of Matter

• Matter exists in four states, namely solid, liquid, gas and plasma.
• These different states of matter have distinct properties which can be used to identify them.

Solids

• Solids hold a fixed shape and volume.
• The particles of solids are tightly packed together, causing them to vibrate on the spot.
• Crystalline solids have regular repeating patterns in their particle arrangement. For example, salt and diamond.
• Amorphous solids have irregular particle arrangements. For example, glass and plastic.

Liquids

• Liquids have a definite volume but no definite shape. They take the shape of the container they are in.
• Liquid particles are less closely packed than solids but more so than gases. Their particles slide past each other.
• Viscosity is a property of fluids (liquids and gases) that indicates the resistance to flow. A liquid like honey, which flows slowly, has a high viscosity.

Gases

• Gases have no definite shape or volume.
• The particles of a gas move freely in all directions, which means the gas spreads out and fills any container it is placed in.
• Pressure in gases is caused by gas molecules colliding with the walls of its container.

Changes in States

• Changes in states of matter are caused by varying the temperatures and pressures.
• The names of the state changes are: melting (solid to liquid), freezing (liquid to solid), evaporation (liquid to gas), condensation (gas to liquid), sublimation (solid to gas), and deposition (gas to solid).

The Kinetic Particle Theory

• This theory helps to explain changes in states of matter.
• It considers the movement of particles in solids, liquids and gases - in a solid, the particles have the least kinetic energy, while in a gas, they have the most.
• As one state changes to another (for example, when a solid is heated and turns into a liquid), the average kinetic energy of the particles increases.