Developing the model of the atom: Atomic structure: Physics: GCSE (9:1)

• Atom

  Building block of matter

  
• J J Thomson


  Discovered the electron and went on to propose that the atom looked like a plum pudding

  
• Plum Pudding model


  An atom is a sphere of positive charge, with negatively charged electrons in it

  
• Ernest Rutherford


  Eonducted an experiment to test the plum pudding model

  
• Alpha particle scattering experiment

  An experiment carried out by two students of Ernest Rutherford where they directed a beam of alpha particles at a very thin gold foil suspended in a vacuum

  
• Alpha particles


  A type of nuclear radiation with a positive charge

  
• Expected results from experiment

  The alpha particles should have passed straight through the foil undeflected

  
• Actual results from experiment

  Most of the alpha particles did pass straight through the foil but a small number of were deflected by large angles and a very small number of alpha particles reflected straight back off the foil

  
• conclusions from experiment

  the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged
• Nuclear model


  An atom is mostly empty space with a positively charged nucleus in the centre that contains most of the mass and electrons orbiting the nucleus

  
• Niels Bohr


  Adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances

  
• James Chadwick


  Provided the evidence to show the existence of neutrons within the nucleus

  
• Current model of the atom

  An atom is mostly empty space with protons and neutrons contained in the nucleus and electrons orbiting the nucleus in different energy levels

  
• What happens to electrons when an atom absorbs energy

  Electrons at a particular energy level jump to higher levels (at larger distances from the nucleus)

  
• When electrons in an atom move to a lower energy level


  The atom emits energy, releasing it as a specific frequency of light