chemistry

chemistry

1. atomic structure and the periodic table

   • atoms
     • particles and mixtures
       • dilution
         • A solution is made when a solute, usually a soluble solid compound, is dissolved into a liquid called a solvent, typically water.
         • If the solute is white (eg sodium chloride) then the solution is colourless. This is because the individual particles (in this case, ions) in the sodium chloride crystals break apart and spread out through the water.
         • If the solute is coloured (eg blue copper sulfate) then the solution will have a colour. As with the white solute, the particles are now too small to see, and evenly spread out.
         • Adding more water to copper sulfate solution will make it a paler shade of blue, because the blue particles will now be further apart. This shows that both the solute and solvent are made from tiny particles.
       • diffusion
         • in gases
           • When chemicals, like the smell of perfume or burning toast, are let loose in a room, the particles mix with the air particles. The particles of smelly gas are free to move quickly in all directions. They eventually spread throughout the whole room. This is called diffusion. Diffusion in gases is quick because the particles in a gas move quickly. It happens even faster in hot gases.
         • in liquids
           • Diffusion can also happen in liquids. This is because the particles in liquids can move around each other, which means that eventually they are evenly mixed. For example, if you drop a little bit of paint into a jar of water the colour will spread slowly through the water by diffusion. Diffusion in liquids is slower than in gases because the particles in a liquid move more slowly.
         • in solids
           • Diffusion does not happen at all in solids because the particles in a solid can only vibrate on the spot, rather than being able to move from place to place.
       • simple distilation
         • Distillation separates a liquid from a solution. For example, water can be separated from salty water by simple distillation. This method works because the water evaporates from the solution, but is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.
   • structure of an atom
     • The protons and neutrons are found in the nucleus at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in shells around the nucleu

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