States of Matter

• Everything is made of matter
• Three states of matter

  • Solid
  • Liquid
  • Gas
• Particle model


  A simple model used to describe the three states of matter
• Particle model


  • Particles are represented by small solid spheres
  • Can be used to explain how particles are arranged and move in solids, liquids and gases
• Particles in solids


  • Have a regular arrangement
  • Are very close together
  • Vibrate about fixed positions
• Particles in liquids


  • Have a random arrangement
  • Are close together
  • Flow around each other
• Particles in gases

  • Have a random arrangement
  • Are much further apart
  • Move very quickly in all directions
• Key Point


  This particle model does have some limitations. It does not take into account:

  . the forces between the particles

  . the volume (although small) of the particles

  . the space between particles
• Changing states


  • Particles stay the same
  • Arrangement of particles changes
  • Movement of particles changes
• Melting point


  The temperature at which a pure substance melts
• Boiling point


  The temperature at which a pure substance boils
• The amount of energy required for a substance to change state depends on the amount of energy required to overcome the forces of attraction between the particles
• The stronger the forces of attraction

  • The greater the amount of energy needed to overcome them
  • The higher the melting and boiling point will be
• Substances with high melting points

  • Ionic compounds
  • Metals
  • Giant covalent structures
• Substances with small molecules

  • Strong covalent bonds within molecules
  • Weak forces of attraction between molecules
  • Only a little energy needed to overcome forces between molecules
  • Relatively low melting and boiling points
• Key Point


  The stronger the forces between particles, the higher the melting point of the substance
• Identifying the State of a Substance

  . The melting point and boiling point of a substance can be used to identify its state at a given temperature
• State Symbols


  . Chemical equations are used to sum up what happens in reactions

  . State symbols show the state of each substance involved

  - (s) - solid

  - (l) - liquid

  - (g) - gas

  - (aq) - aqueous (dissolved in water)

  . For example, when solid magnesium ribbon is added to an aqueous solution of hydrochloric acid:

  - a chemical reaction takes place

  - a solution of magnesium chloride is produced

  - hydrogen gas is produced

  . This can be summed up in a symbol equation