OCR GCSE Chemistry

## States of matter Matter is made of tiny particles, and the **particle model** uses that idea to explain how solids, liquids and gases behave. In the simplest version each particle is drawn as a small solid sphere, and the states differ in how the particles are arranged and how they move. | State | Arrangement | Movement | Density and shape | |---|---|---|---| | Solid | Closely packed, usually in a regular pattern | Vibrate about fixed positions | High density, fixed shape and volume | | Liquid | Closely packed, irregular | Move past one another | High density, fixed volume, takes the shape of its container | | Gas | Far apart, irregular | Move quickly in random directions | Low density, fills its container | Solids and liquids are hard to compress because their particles are already touching. A gas can be compressed because most of it is empty space between the particles, which is also why gases have such low densities. Gas particles fill a container because they are free to travel until they hit a wall, and the collisions with the walls are what produce gas pressure. Particles in a liquid or gas are always moving, and this is the reason for diffusion. If a drop of coloured solution goes into water, or a scent is released in one corner of a room, the particles spread out from where they are crowded into the space around them without anyone stirring. Diffusion is faster in gases than in liquids because gas particles are further apart and move faster. Elements are…