Understanding the Particle Model of Matter for GCSE Physics

The Particle Model of Matter

The particle model explains the properties of the three states of matter - solids, liquids, and gases - based on the arrangement and behavior of their constituent particles (atoms or molecules).

Solids

• Particles are closely packed in a regular, ordered arrangement.
• Particles vibrate about fixed positions, held together by strong attractive forces.
• Solids have a definite shape and volume, with high density.

Liquids

• Particles are randomly arranged, but still close together.
• Particles can slide over each other, with weaker attractive forces than solids.
• Liquids have no fixed shape, but a definite volume and high density.

Gases

• Particles are randomly arranged and far apart, with negligible attractive forces.
• Particles move rapidly in all directions, colliding with each other and container walls.
• Gases have no fixed shape or volume, with low density.

Density

Density is the mass per unit volume of a substance. It can be calculated as:

density = mass / volume

Worked Example

Problem: Find the density of a 500 g block with dimensions 5 cm x 10 cm x 2 cm.

Solution:

• Mass = 500 g = 0.5 kg
• Volume = 5 cm x 10 cm x 2 cm = 100 cm³ = 0.0001 m³
• Density = mass / volume = 0.5 kg / 0.0001 m³ = 5000 kg/m³

Internal Energy and Thermal Physics

Internal energy is the total kinetic and potential energy of particles in a substance. Heating increases internal energy by:

• Raising the temperature (increasing particle kinetic energy)
• Causing a change of state (overcoming particle attractive forces)

Key concepts:

• Specific heat capacity: the energy required to raise 1 kg of a substance by 1°C
• Specific latent heat: the energy absorbed or released during a change of state per unit mass
• Energy required for state change: E = mL, where m is the mass and L is the specific latent heat

Gas Laws

For a fixed mass of gas, pressure (P), volume (V), and temperature (T) are related as:

• Pressure ∝ 1/Volume (at constant T)
• Pressure ∝ Temperature (at constant V)

This behavior arises from particle collisions with container walls. Higher temperature means greater particle kinetic energy and more frequent collisions.