States of matter
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Solids are formed when a substance is cooled to below its melting point. The atoms in a solid don't have enough energy to break their intermolecular forces, so they can be modelled as tightly packed spheres. Only solid metals can conduct electricity, as they have free electrons that can carry the charge.
Liquids are formed when a substance is held above its melting point but below its boiling point. The atoms have enough energy to partially break their intermolecular forces, giving them more flexibilty to move around in space. Molten metals and ionic substances have free moving charged particles, allowing them to conduct electricity.
Gases are formed when a substance is warmed to above its boiling point. The atoms have enough energy to completely break their intermolecular forces, giving them to freedom to move around in space.
When writing chemical equations, state symbols are used to indicate which physical state each compound is in. They're written in subscript after the molecule. (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous.
Substances can change their physical state via a range of physical processes.
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