C1 - atomic structure

• An element contains only one type of atom
• elements in the same group have:

  • the same number of electrons in their outer shell
  • similar properties

  elements in the same period have:

  • the same number of electron shells
• compounds are 2 or more elements that are chemically bonded and are made in chemical reactions
• what is a mixture?

  Two or more different atoms which are not chemically bonded - can be separated
• what is the reactant?

  what you start with in a chemical reaction
• what is a product?

  what is made in a chemical reaction
• the conservation of mass:

  • in a chemical reaction, chemical bonds are broken and the atoms are rearranged and the chemical bonds are made again
  • in a chemical reaction, mass is never lost, you must start and finish with the same mass
• a pure substance contains only one type of element/compound
• an impure substance contains more than one type of element/compound in a mixture e.g. salt water contains NaCl and H2O - all mixtures are impure substances
• mixtures are much easier to separate than elements/compounds - not chemically bonded
• ways for separating impure substances:

  • chromotography
  • Distillation
  • crystalisation
• Chromatography:

  • different substances travel different distances up the paper depending on their solubility in the solvent used. The more soluble, the further it moves up the paper
  • line must be drawn with pencil - wont run
• distillation:

  • when 2 liquids with different boiling points are separated e.g. ethanol boils at 78 degrees Celsius and water boils at 100 degrees celcius
  • if you heat the mixture of water and ethanol to 80 degrees the ethanol will evaporate but the water wont
  • then condense the ethanol and collect pure ethanol
• crystalisation is when a solvent is evaporated from a solute
• protons and neutrons are found in the nucleus whilst electrons are found orbiting the nucleus in shells
• the mass and charges o the sub atomic particles:

  mass:

  proton - 1

  neutron - 1

  electron - 0

  charge:

  proton - +1

  neutron - 0

  electron - -1
• Atoms have no overall charge because they have the same numbers of positive protons and negative electrons