C1.1 (the particle model)

• what does the particle model show?

  How particles are arranged and how they move in solids, liquids and gases
• Why can you not compress a substance in a solid or liquid state?

  There is no space for the particles to move in to
• why does a substance in a solid state have a fixed shape and cannot flow?

  The particles vibrate around fixed positions and cannot move around
• what is a physical change?

  When a substance changes state or shape, or breaks into pieces and no new substances are made, many physical changes can be reversed
• give some examples of physical changes?

  Freezing juice, mixing sand with water or dissolving sugar in water
• what is a chemical change?


  A change that produces one or more new substances, the properties of the new substances are often very different from the properties of the original substances
• Give some examples of chemical changes


  cooking eggs or cakes, steel rusting or an acid and an alkali reacting to make a salt and water
• what happens to the particles when a substance changes state?

  The actual particles stay the same but the arrangement and movement changes
• what happens to particles in a chemical change?

  They break up and join together in different ways, forming new substances
• what are the smallest particles that make up a substance called?

  Atoms
• what are the smallest atoms?

  Helium atoms
• what is the diameter of a helium atom?

  62 x 10 ^ -12 m
• what is the equation for the ratio of distance to diameter in an atom?


  Distance between atoms ÷ diameter of atom
• what are forces between particles called?

  Electrostatic forces of attraction, between positive and negative charges
• where are electrostatic forces of attraction strongest?


  Strongest in solids, weakest in gases. the forces become weaker the further apart the particles are
• what are the limitations of the particle model?


  It does not show:

  the forces between particles

  the size of particles

  the space between particles