Atomic Structure

• Which sub-atomic particle was discovered first?

  Electron
• Describe the plum pudding model

  J.J Thomson suggested that atoms were spheres of positive charge with negatively charged electrons scattered throughout like plums in a pudding.
• Describe the gold foil alpha scattering experiment

  In 1909, Rutherford fired a beam of alpha particles at thin gold foil. They expected the particles to pass straight through or be slightly deflected, however some deflected straight back while most went right through. This meant that most of the mass of the atom must be concentrated at the centre in a nucleus
• Who discovered the neutron?

  James Chadwick
• What is the charge of a proton?

  +1
• What is the charge of a neutron?

  0
• What is the charge of an electron?

  -1
• What did Niels Bohr suggest about the nuclear model of the atom?

  That electrons orbiting the nucleus do so at certain distances called energy levels.
• What is an isotope?

  An isotope of an element are atoms with the same number of protons but a different number of neutrons
• How does alpha radiation occur?

  When an alpha particle is emitted from the nucleus of an atom.
• What are alpha particles made up of?

  Two neutrons and two protons
• What levels of penetration and ionisation are alpha particles?

  Low penetration, highly ionising - can only travel a few cm in air and absorbed by a sheet of paper.
• What is a beta particle?

  A fast moving electron released by the nucleus of an atom,
• What levels of penetration and ionisation are beta particles?

  Moderately ionising and moderately penetrating - range in air of a few metres, absorbed by a 5mm sheet of aluminium
• Finish the sentence: for every beta particle emitted, a neutron in the nucleus has turned into a....

  Proton
• What are gamma rays?

  EM waves with a short wavelength
• What level of penetration and ionisation are gamma rays?

  Highly penetrating, weakly ionising - travels long distance without being stopped, pass through atoms rather than collide
• What is half-life?

  The half-life is the time taken for the number of radioactive nuclei in an isotope to halve.