We live in a gaseous atmosphere surrounded by plasma with plasma the fourth and most abundant state of matter.

This resource provides explanations of the key concepts, such as the structure, properties and uses, encountered when investigating gases and plasmas.

States of matter

The classical states of matter are solid, liquid and gas. Several other states, such as plasma, do exist. Plasma is the most common form of matter in the universe.

Kinetic-molecular theory of matter

This theory states that all matter is made up of extremely small particles (atoms, molecules or ions) that are in constant motion.

The gaseous state

The kinetic-molecular theory describes the gaseous state as one in which gas particles are spaced out relative to one another and are moving around with rapid, random motion.

Properties of gases


  • fill the entire containing vessel
  • diffuse freely when mixed
  • are easily compressed
  • expand rapidly when heated
  • exert a gas pressure.

The plasma state

Plasma is the highest energy state of matter consisting of a collection of free-moving electrons, positive ions and neutral particles. It is ionised gas and makes up 99% of all matter in the known universe.

Plasma properties


  • have a very high electrical conductivity
  • are more readily influenced by electric and magnetic fields than by gravity
  • produce their own electric and magnetic fields
  • produce their own electromagnetic radiation.

Latent heat of vaporisation

Converting a liquid at its boiling point to a gas at the same temperature requires an input of heat energy. The amount needed is called ‘latent heat’.


The flow of energy from a body at higher temperature to one at lower temperature when they are placed in thermal contact.

Heat energy

The energy in materials that relates to the temperature and random movement of the particles in that material. This energy of random particle movement can be transferred naturally from one high-temperature or hot material to another low-temperature or cold material.

Heat pump

A device that can pump thermal energy either into (heating) or out of (cooling) an enclosed space such as a house.

Thermal energy

All forms of matter have internal or thermal energy. This comes about as a result of particle motion (kinetic energy) as well as the energy stored in chemical bonds present in the particles themselves (potential energy).


The branch of science concerned with heat and its relation to energy and work.


The process occurring within the plasma core of our Sun in which the nuclei of lighter atoms link to form a heavier atom. This process releases tremendous amounts of energy.

Fusion reactors

Over the last 50 years, scientists have thoroughly investigated the development of nuclear fusion reactors that can transform fusion energy into electrical energy for public consumption.

Solar wind

The stream of charged particles ejected at high speed from the outer layer of the Sun. It is rapidly moving plasma.


A luminous glow of the upper atmosphere, often seen in high latitudes close to the poles. The more intense the solar wind, the more spectacular the aurora’s display of coloured lights.


A large-scale natural spark discharge that occurs within the atmosphere or between the atmosphere and the Earth’s surface. The lightning channel is an example of terrestrial plasma in action.

    Published 29 April 2014