physics - atomic structure

• Dalton said that matter was made up of tiny spheres (atoms that could not be broken up


  1804
• JJ Thomson discovered electrons that could be removed from atoms


  1897
• Dalton's theory wasn't right - atoms could be broken up
• Thomson's model of the atom

  Atoms were spheres of positive charge with electrons embedded in them
• Rutherford carried out the Gold foil Experiment


  1909
• Gold foil Experiment


  1. Fired alpha particles at a thin sheet of gold

  2. Most particles went straight through due to the atom being mostly empty space

  3. Some were deflected backwards as the nucleus is small + dense
• Current model of the atom

  • The nucleus contains protons and neutrons
  • Electrons move around the nucleus
• Isotopes


  Atoms of the same element have the same number of protons but a different number of neutrons
• Isotopes


  • Carbon-12
  • Carbon-13
• All elements have different isotopes, but there are usually one/two stable ones
• Unstable isotopes decay into other elements and give out radiation as they try to become more stable
• Radioactive decay


  Radioactive substances emit one or more ionising radiation from their nucleus - alpha, beta, gamma
• Ionising radiation


  Radiation that knocks electrons off atoms, creating positive ions