On earth, we commonly find three states of matter: solid, liquid, and gas.

The molecules of water move differently depending on the state of matter. In the gas form they move freely, in the liquid form they have a more restricted range of movement, and in the solid form they are not changing positions, but vibrating in place

Figure 1. Three states of water molecules.

  • Solid is rigid; it has both a fixed shape and volume.
  • Liquid assumes the shape of its container; it has a distinct volume but has no specific forms.
  • Gas, also known as vapor, takes the volume and shape of its container; it has no definite shape and volume.

The molecular arrangement of the molecules in the substance determines the different properties of solid, liquid, and gas.

In some high-temperature environments (for example the interior of stars, TV screens, or lightning strikes), we could find another state of matter called plasma. Plasma is a gaseous state of matter that contains a number of electrically charged particles.