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• An atom is the smallest part of an element.
• A chemical reaction leads to the formation of one of more new substances. Sometimes an energy change is involved.
• An element is a substance made up from only one type of atom.
• A mixture is when different elements or compounds are not chemically joined together and can be seperated.
• An ion is an atom that has gained or lost electrons to become a charged practicle.
• Elements are arranged in order of atomic number.
• In the periodic table:

  • Groups are vertical
  • Periods are horizontal
• Symbol equations must be balanced as elements are never created or destroyed. This means there are always the same number of atoms in both the reactants and products.
• An ionic equation is similar to a symbol equation but only includes the ions that react.
• Ions that do not take part in a chemical reaction are known as spectator ions.
• A half equation applies to a specific type of reaction, which involves the change in oxididation number of an atom or ion.

  These reactions are known as redox reactions, where an atom or ion either:

  • Loses electrons (oxidation)
  • Gains electrons (reduction)
• Atoms contain protons, neutrons and electrons.
• The nucleus contains protons and neutrons.
• Electrons move around the nucleus in electron shells.
• The nucleus has a positive charge.
• Atoms have a neutral charge.
• The atomic number shows the amount of protons there is.

  The mass number shows you the total amount of protons and neutrons there are.
• Isotopes:

  Different forms of the same element, which have the same number of protons but a different number of neutrons.
• Isotopes have the same atomic number but different mass numbers.
• Compounds are held together by chemical bonds.
• A compound formed from a metal and a non-metal consists of ions. The metal atoms lose electrons to form positive ions and the non-metal atoms gain electrons to form negative ions. The opposite charges of the ions mean that they're strongly attracted to each other. This is called ionic bonding.
• A compound formed from non-metals consists of molecules. Each atom shares an electron with another atom - this is called covalent bonding.
• Filtration is removing an insoluble solid from a liquid.
• Simple distillation is separating a mixture based on boiling points
• Fractional distillation is separating boiling points, which are very close together.
• Crystallisation is forming a soluble solid from a solution.
• Chromatography is separating a mixture based on solubility.
• Filtration:

  • Used to separate an insoluble solid from a liquid.
  • When filtered, the solid remains in the filter paper. This is known as the residue.
  • The substance that passes through the filter paper is known as the filtrate.
• Distillation:

  • Separates mixtures based on different boiling points.
  • The mixture is heated to a gas.
  • Both simple and fractional distillation involve a condenser (allows the gas to turn back into a liquid) and thermometer (allows the correct part of the mixture to be collected).
  • Fractional distillation includes a fractioning column (increases the separation time).
• Crystallisation:

  • Used to obtain a soluble solid from a solution.
  • The solvent is removed by evaporation.

  - To encourage large crystals to form, the solvent is evaporated by

  gentle heating until crystals start to form. If the solvent is

  evaporated quickly, then small crystals would form.
• Chromatography:

  • Used to separate a mixture based on solubility.
  • The solvent rises up the paper and dissolves the sample. The more soluble parts of the mixture travel further up the paper.
  • The level that the solvent travels to is known as the solvent front.
  • Comparing an unknown mixture with known samples allows us to identify components.

  - A positive match is when the spots in both the mixture and a

  known sample travel to the same height and create the same

  number of spots.
• Protons are a subatomic particle that is positively charged and found in the nucleus.
• Neutrons are a subatomic particle with no charge and is found in the nucleus.
• Electrons are a subatomic particle that is negatively charged and orbits the nucleus in shells.
• Relative atomic mass is the mass of protons and neutrons in an atom.
• Atomic number is the number of protons and electrons in an atom.
• When elements lose electrons, they become positive ions; they become negative ions when they gain electrons. 
• Electron structure:

  • 1st shell: 2 electrons
  • 2nd shell: 8 electrons
  • 3rd shell: 8 electrons
• Isotopes have the same number of electrons, so they have similar chemical properties. Isotopes have different numbers of neutrons, so they have different physical properties.
• Models of the atom:

  1. Dalton
  2. Thomson
  3. Rutherford
  4. Bohr
  5. Chadwick