In general, but not in all specific cases, as the temperature increases and pressure decreases substances pass through the four different states.
Almost all the observable matter in the universe exists in the plasma state.
The plasma state of matter is characterized by the following:
- charge separation by ionization: a plasma is a gas whose atoms have lost some or all of their electrons - it is a gas of ions and electrons
- a plasma has no definite shape or volume
- plasmas are overall electrically neutral, containing balanced numbers of positive and negative charges.
- plasmas are electric conductors, whereas gases are insulators
- plasmas form at very high temperatures: the higher the temperature and the lighter the element, the more fully ionized the plasma's atoms are likely to be:
- the solar corona and the interior of the sun are fully ionized plasmas
- lightning strikes consist of partially ionized plasmas, as do electric sparks
- lights based on ionized noble gases, such as neon lights, contain partially ionized plasma
- at lower temperatures, plasma may contain un-ionized neutral species, whose proportion falls as the temperature rises
- average speeds of particles in plasmas are higher than in gases, with a higher proportion of atomic- and molecular-sized particles moving at very high speeds
The image below is a neon light. A high voltage is applied to neon at low pressure, ionizing it to produce a plasma.