Exploring the Particle Model of Matter in GCSE Physics

The Particle Model of Matter

The particle model of matter describes the behavior and properties of substances based on their fundamental particles and the forces between them. In GCSE Physics, this model explains the three states of matter: solids, liquids, and gases.

States of Matter

• Solids: Particles are closely packed, vibrating about fixed positions with strong attractive forces between them. Solids have a definite shape and volume.
• Liquids: Particles are still closely packed but can slide past each other. Attractive forces are weaker than in solids, allowing liquids to flow and take the shape of their container, while maintaining a fixed volume.
• Gases: Particles are widely spaced, moving randomly in all directions with negligible attractive forces between them. Gases have no definite shape or volume, taking the shape and volume of their container.

Density

Density is the measure of a substance's mass per unit volume. It is calculated as:

Density = Mass / Volume

For regular solids and liquids, the density can be determined experimentally by measuring the mass and volume. For irregular shapes, the displacement method can be used to find the volume.

Worked Example

Problem: A solid cube with sides of 10 cm has a mass of 2.7 kg. Calculate its density.

Solution:

• Volume of cube = side length × side length × side length = 10 cm × 10 cm × 10 cm = 1000 cm³ = 0.001 m³
• Density = Mass / Volume = 2.7 kg / 0.001 m³ = 2700 kg/m³

Internal Energy and Changes of State

Internal energy is the total kinetic and potential energy of particles in a substance. Heating a substance increases its internal energy, either by increasing the temperature (increasing particle motion) or causing a change of state (overcoming attractive forces between particles).

Specific heat capacity and specific latent heat are used to calculate the energy required for these changes:

• Specific Heat Capacity: Energy required to change the temperature of 1 kg of a substance by 1°C.
• Specific Latent Heat: Energy required to change the state of 1 kg of a substance, given by the equation: E = mL, where E is the energy, m is the mass, and L is the specific latent heat.

Gas Laws

For a fixed mass of gas, the pressure, volume, and temperature are related through particle collisions and kinetic energy. As temperature increases, particles move faster, causing more frequent and forceful collisions with the container walls, increasing the pressure. Similarly, increasing the volume decreases the pressure by reducing the frequency of collisions.

These relationships can be explored through experiments and calculations involving gas laws, such as Boyle's Law, Charles' Law, and the Ideal Gas Law.

For further reading and practice, refer to the BBC Bitesize guide on the particle model and exam board specifications from OCR, AQA, Edexcel, and WJEC.