Physics Atomic Structure/ Radiation (Higher)

• 1. John Dalton 19th C: Atoms were solid spheres
• 2. JJ Thompson 1897: Plum pudding
• 3. Ernest Rutherford 1909: Scattering experiment, mass is concentrated in the centre and atoms are empty space
• 1. Niels Bohr 1913: Electrons orbit nucleus at fixed energy levels
• 4. Niels Bohr 1911: Electrons in shells orbiting nucleus
• James Chadwick 1940: Neutrons in nucleus discovered
• Isotope: an element with the same number of protons but a different number of neutrons. Same atomic number but different mass numbers.
• Alpha: 2 protons 2 neutrons, cant travel too far, highly ionising due to size
• Beta: fast moving electron, can be stopped by aluminium, emitted by atom when a neutron splits into a proton and an electron
• Gamma: Most penetrating, stopped by thick lead and concrete. Least ionising
• Half life: The time taken for the number of nuclei in an isotope to halve.
• Irradiation: when materials are near a radioactive source
• Alpha Decay Equations: An alpha particle is made of 2 protons 2 neutrons. Atomic number goes down by 2 and mass number decreases by 4
• Beta Decay Equations: A neutron turns into a proton and releases an electron. Mass of the nucleus does not change but the number of protons increases.
• remember!

  Protons= bottom number

  Electrons= bottom number

  Neutrons= top number-bottom number