Chemistry

• The concentration equation is :

  concentration = mass / volume
• Solids:

  • have a fixed volume and a fixed shape
  • Electricity cannot flow, because their particles cannot move from place to place
  • cannot be compressed, because their particles are close together and have no space to move into
• Liquids:

  • have a fixed volume but no fixed shape 
  • can flow and take the shape of their container, because their particles can move around each other
  • cannot be easily compressed, because their particles are close together and have no space to move into
• Gases:

  • have no fixed shape or volume
  • can flow and completely fill their container, because their particles can move quickly in all directions
  • can be compressed, because their particles are far apart and have space to move into
• Atoms are tiny particles that are far too small to see, even with a microscope.To make diagrams simpler we often draw atoms as circle
• An element is a substance that is made up of only one kind of atom.
• A compound is a substance that contains atoms of two or more different elements, chemically joined together.
• A mixture contains different substances that are not chemically joined to each other. 
• Mixtures can usually be separated by physical techniques such as filtering and distillation
• Filtration

  This technique is used to separate an insoluble solid from a liquid. It can be used to obtain a product that is free from unreacted chemicals, by-products or solvent
• Evaporation

  One way to separate a soluble solid from its solution is to make crystals. This involves evaporating the solution to a much smaller volume and then leaving it to cool. As the solution cools, crystals form, and these can be obtained by filtration.
• Simple distillation

  Distillation separates a liquid from a solution. . This method works because the water evaporates from the solution, but is then cooled and condensed in a condenser and collected in a separate container. The salt does not evaporate and so it stays behind.
• Chromatography can be used to separate mixtures of coloured compounds
• Simple chromatography A spot of the mixture is placed on a pencil line near the bottom of a piece of chromatography paper The paper is then placed upright in a suitable solvent, such as water. As the solvent soaks up the paper, it carries the mixtures with it. Different components of the mixture will move at different rates. This separates the mixture out.
• Water purification.

  • Sedimentation – the water is stored in a large tank or a reservoir. This slows down the flow of the water and allows large, insoluble particles to settle to the bottom. The cleaner water at the top can then be extracted for the next stage.
• Water purification

  • Filtration – the water is sprayed onto specially-prepared layers of sand and gravel. As it trickles through, smaller insoluble particles are removed. The filter beds are cleaned periodically by pumping clean water backwards through the filter.
• Water purification

  • Chlorination – chlorine gas is injected into the water to sterilise it. The chlorine is poisonous and so kills microorganisms.
• Atoms contain three sub-atomic particles called

  protons , neutrons and electrons

  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 nucleus.
• An atomic number is the number shown below the symbol and is the number of protons
• The total number of protons and neutrons in an atom is called its mass number which is above the symbol.
• Isotopes have different numbers of neutrons but the same number of protons.
• Mendeleev arranged the elements in order of increasing relative atomic mass. He then arranged the elements by putting those with similar properties below each other into groups.
• Relative atomic mass = average mass/1200