Atoms and elements

• isotopes are atoms with the same number of protons and different number of neutrons
• an element is a substance made of only one type of atom
• a compound is a substance made of 2 or more different elements chemically combined together
• a mixture consists of 2 or more elements or compounds not chemically combined together
• John Dalton- 1803-Atoms are solid spheres that are indivisible

  JJ.Thompson- 1897-The atom is a sphere with positive and negative charges embedded in it

  Ernest Rutherford- 1911-Electrons orbit a positively charged nucleus, the atom is empty spaced (later on discovered proton)

  Niels Bohr- 1913-Electrons travel in separate orbits around the nucleus

  James Chadwick- Discovered the neutron
• What is chromatography?


  a process for separating components of a mixture
• What is simple distillation?

  purifying a liquid by heating it into a vapour that is then condensed back into a liquid
• What is fractional distillation?


  separates a mixture into a number of different parts, called fractions
• What is crystallisation?


  the process of forming solid crystals from a solution by allowing the solvent to evaporate slowly
• What is filtration?


  used to separate a solid from a liquid