Atoms, ions and molecules
In gas, the particles are far apart. In liquid, the particles are closer together. In solid, they are even closer than liquid. Physical state of matter is called solid, liquid and gas. These can commonly be defined by their physical characteristics.
Solid, liquid and gas have fixed mass. Solids have fixed volume and shape. Liquid has fixed volume but not fixed shape and gasses have neither fixed volume nor shape. Liquids and gasses take up the shape of the container.
All liquids can flow or poured from one container to another. But some liquids flow faster than other liquids. The more viscous the liquid the more time it takes to flow because of the friction between its molecule. Water is an example of liquid that has low viscosity so the molecules are free to move easily.
Among the three states, gas is highly compressible compared to liquid, where solid is incompressible. Solid and liquid have higher density than gas.
The particles of solid are not free to move the same way as the particles of gas or liquid. These particles are held together by forces that keep them close to each other. However, even the particles of solid show constant movement. They vibrate back or forth as if they are attached to little springs. When heat is added to a solid, the particle’s speed up and exhibit bigger vibrations.
The particles of liquid stay close together. It is because the forces among particles are stronger than those in gas but weaker than those in solid. The particles in gas on the other hand, can move freely because they are very far apart compared to solid and liquid.