States of Matter (Solid, Liquid, Gas)

Particle Arrangement

The arrangement of particles differs in solids, liquids, and gases, affecting their properties:

• Solids: Particles are tightly packed in a fixed, regular pattern. They are very close together with almost no space between them.
• Liquids: Particles are close together but not in a fixed pattern. They can move past each other, allowing liquids to flow.
• Gases: Particles are far apart with lots of space between them. They move independently and freely in all directions.

For example, in a solid like ice, water molecules are locked in place in a crystal lattice. In liquid water, molecules are close but slide around each other. In steam (water vapour), molecules are widely spaced and move randomly.

Particle Movement

The movement of particles varies with the state of matter:

• Solids: Particles vibrate about fixed positions but do not move from place to place.
• Liquids: Particles move by sliding past each other, allowing the liquid to flow and change shape.
• Gases: Particles move rapidly and randomly in all directions, colliding with each other and the container walls.

This explains why solids keep their shape, liquids flow to fit their container, and gases fill any available space.

For instance, in a solid metal rod, atoms vibrate but stay in place, while in liquid mercury, atoms slide over each other, and in mercury vapour, atoms move quickly and randomly.

Shape and Volume

The differences in particle arrangement and movement affect the shape and volume of solids, liquids, and gases:

• Solids: Have a fixed shape and fixed volume because particles are locked in place.
• Liquids: Have a fixed volume but no fixed shape. They take the shape of their container because particles can move around.
• Gases: Have no fixed shape or volume. They expand to fill the entire volume of their container.

For example, a block of wood keeps its shape and volume, water in a glass keeps its volume but takes the glass’s shape, and air in a balloon expands to fill it.

Energy and States

Heating a substance transfers energy to its particles, affecting their movement and arrangement:

• As particles gain energy, they move faster and vibrate more vigorously.
• In solids, increased energy causes particles to vibrate more until they break free during melting.
• In liquids, particles move faster and can escape into the gas phase during boiling.
• Energy transfer is involved in changing states, but the detailed processes of melting, boiling, and evaporation are covered in other topics.

For example, heating ice causes particles to gain energy and vibrate more until the solid melts into liquid water.

The energy gained or lost during state changes is called latent heat (see Changes of State topic for more). Latent heat is the energy required to change the state of a substance without changing its temperature.

Learning Example: Particle Movement and State

Imagine a container of water at room temperature (liquid). The particles are close but move around each other. If you heat the water, particles gain energy and move faster. Eventually, at 100°C, they have enough energy to break free from the liquid and become gas particles moving rapidly and far apart.