Density of solids, liquids and gases

The difference between the densities of solids, liquids and gases is due to the distance between the particles in each state of matter.

Solids and liquids

The particles of a solid are very close together.

It melts when it changes from the solid state to the liquid state.

The particles remain close together, so there is usually only a small increase of volume.

The same mass of liquid will have slightly greater volume than the solid.

As density equals \frac{\text{mass}}{\text{volume}}, the liquid will have slightly lower density.

The density of solid iron = 7.8 g/cm3

The density of liquid iron = 6.9 g/cm3

Liquids and gases

A substance evaporates when it changes from the liquid state to the gas state.

Its particles move freely and are very far apart, so there is a large increase of volume.

The same mass of gas will have very much greater volume than the liquid, and so will have much lower density.

The density of liquid oxygen = 1.1 g/cm3

The density of gaseous oxygen = 0.0014 g/cm3

StateDistance between particlesDensityDensity in g/cm3
SolidVery close togetherHighSolid iron = 7.8
LiquidSlightly further apart than a solidSlightly less than the solidLiquid iron = 6.9
GasVery much further apart than a solid or liquidVery much less than the solid or liquidOxygen gas = 0.0014
Flow chart showing the particle model changes between solid, liquid and gas, as internal energy is increased.