4-Atomic structure

• history of the atom

  1. Democritus- everything made from tiny particles, can't be broken down, separated by empty space
  2. Dalton- solid spheres, diff types make up diff elements
  3. Thompson- plum pudding- ball of positive charge with electrons scattered around
  4. Rutherford- alpha scattering exp- nuclear model- positive charge nucleus, negative charge cloud around it
  5. Bohr- electrons orbit nucleus in shells
  6. Rutherford- protons
  7. Chadwick- neutrons
• radioactive decay is the process in which unstable isotopes emit particles and energy such as alpha, beta or gamma radiation or just neutrons to decay into other elements and become more stable
• electrons

  • arranged in energy levels (shells)
  • they can increase an energy level if they gain enough energy which makes it 'excited'
  • an electron does this due to electromagnetic radiation
  • it will soon decrease it's energy level and re-emit the energy as electromagnetic radiation
• ionisation - ionisation radiation

  • happens when an electron in the outer shell absorbs so much energy that it is able to leave the atom
  • this leaves the atom with more protons than electrons so it will have a positive charge (positive ion)
• types of radioactive radiation

  • alpha
  • beta
  • gamma
  • neutrons
• types of radiation - alpha α - ⁴₂He

  • made up of 2 protons and 2 neutrons
  • doesn't have electrons so it has a 2+ charge
  • can only move a few cm in the air, cannot penetrate any materials, absorbed by a single sheet of paper
  • they are strongly ionising due to their large size and strong charge
  • often displayed by helium as they are identical
• types of radiation - beta β - ⁰₋₁β

  • just an electron
  • has a 1- charge and has no mass
  • electrons are emitted from one of the atom's neutrons, which decays into a proton and an electron, at high speeds
  • they can penetrate moderately far such as several metres of air, 5 mm of aluminium
  • they are moderately ionising as they are small
• types of radiation - gamma γ - ⁰₀γ

  • aren't particles, they are waves of electromagnetic radiation
  • they are often emitted after alpha or beta radiation as nucleus ridding itself of a bit of extra energy
  • they pass straight through materials as they have no mass or charge such as long distances in the air, thick sheets of lead, multiple metres of concrete
  • they are weakly ionising as they don't collide with particles
• types of radiation - neutron - ¹₀n

  • if a nucleus contains too many neutrons, making it unstable, it can throw out a neutron to increase it's stability
  • this is called beta radiation
• nuclear equations

  • alpha - 4 is subtracted from the atomic mass, and 2 from the atomic number
  • beta - the atomic mass stays the same, the atomic number increases by 1
  • gamma - neither of the numbers change as only energy is emitted
  • neutron - only 1 is subtracted from the atomic mass, the atomic number stays the same

  
• • atomic mass is the top number
  • atomic number is the bottom number
• the decay process is randon
• activity

  • activity is the overall rate of decay of all the isotopes in a sample
  • the units for activity are Becquerels
  • 1Bq = 1 decay per second
• half-life - has two meanings

  • time taken for the number of radioactive nuclei in a sample to halve
  • time taken for the number of decays or activity to halve
• finding activity

  • using a Geiger-muller tube and counter which records all the decays that reach them each second
• as a radioactive sample decays over time, its half life increases