Basic Chemistry/States of matter

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Matter exists in four different forms - solid, liquid, gas, and plasma. These are the four states of matter. You can recognize each state because they have different properties. A property of a material describes how it behaves. This behavior is not observable at the chemical level due to microscopic sized particles. We can observe how many H2O particles behave when we open a faucet, releasing water, which is a lot of H2O particles in their liquid state. Of course we can observe other states of H2O particle groupings, at low temperatures they freeze, demonstrating a solid property. At high temperatures they form a gas called steam.


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  1. Wikipedia: State of matter
  2. Wikipedia: Solid
  3. Wikipedia: Liquid
  4. Wikipedia: Gas

States of matter

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Property Solids Liquids Gases
Volume has definite volume has definite volume has no definite volume-always fills the container they are in
Shape have a definite shape match the shape of the container become the same shape as the container
Density have a high density have a high density have a low density
Compressibility not easily squashed not easily squashed easily squashed
Flow don't flow flow easily flow easily

Particle theory

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  • All materials are made up of particles.
  • The particles that are in a substance (material) stay the same whatever state the substance is in. The only thing that changes is the arrangement of the particles and the energy they have.
  • Whichever state the substance is in depends on how strongly the particles stick together. And how well the particles stick together depends on:
    • the material
    • the temperature
    • the pressure.
  • This is particle theory, and it explains all the different properties of solids, liquids and gases.


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  • They are held tightly together by strong forces of attraction.
  • They are held in fixed positions but they do vibrate.
  • Because the particles don't move, solids have a definite shape and volume, and can't flow.
  • Because the particles are already packed closely together, solids can't easily be compressed.
  • Because there are lots of particles in a small volume, solids are dense.
  • Powdered solids cannot take the shape of their container.


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  • Particles are still touching and held by very strong forces of attraction.
  • They are free to move past each other.
  • Because the particles can move, liquids don't have a definite shape, and they can flow.
  • Because the particles are still packed close together, liquids can't easily be compressed and keep the same volume.
  • Because there are lots of particles in a small volume, liquids have almost the same density as when they are solid. Some, like water are actually more dense than their solid, but most are very slightly less dense.


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  • Particles are far apart from each other because there are very weak forces of attraction between them.
  • They move fast in all directions.
  • Because of this, gases don't have a definite shape or volume and fill any container.
  • Because there is lots of free space between particles, gases can easily be compressed.
  • Because there aren't many particles in a large volume, gases have very low densities typically 1000 times less than in their condensed state as solid or liquid at atmospheric temperature and pressure.