How does density differ between solids, liquids, and gases?

Density differs between solids, liquids, and gases due to the varying arrangement and spacing of their particles.

In solids, particles are tightly packed together in a fixed, orderly arrangement. This close packing means that solids generally have the highest density among the three states of matter. The particles vibrate in place but do not move around, which helps maintain the solid's shape and volume. For example, metals like iron and gold are very dense because their atoms are closely packed in a regular pattern.

Liquids have particles that are still close together but not in a fixed position. They can move around and slide past each other, which allows liquids to flow and take the shape of their container. Because the particles are not as tightly packed as in solids, liquids have a lower density than solids. Water is a common example of a liquid with a density of about 1 gram per cubic centimetre (g/cm³).

Gases have particles that are much further apart compared to solids and liquids. The particles in a gas move freely and rapidly in all directions, filling the entire volume of their container. This large amount of space between particles means that gases have the lowest density of the three states of matter. For instance, the density of air at room temperature is approximately 0.0012 g/cm³, which is much less than that of solids and liquids.

Understanding these differences in density helps explain why certain materials float or sink when placed in a liquid, and why gases are often used to fill balloons and tyres. The arrangement and movement of particles in each state of matter are key factors that determine their density.