The Atom (Cambridge O Level Physics)

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Atomic Structure

  • Atoms are the building blocks of all matter
    • They are incredibly small
  • Atoms have a tiny nucleus at their centre, with electrons orbiting around the nucleus
  • They consist of small positively charged nuclei, surrounded by negatively charged electrons

  

The Structure of an Atom

 

rutherfords-model-of-the-atom

An atom has a small positive nucleus, surrounded by orbiting negative electrons

Rutherford's Experiment

  • In 1909 Ernest Rutherford was investigating their ideas about the structure of the atom
  • This involved the scattering of alpha (α) particles by a sheet of thin metal supports the nuclear model of the atom
  • A beam of alpha particles was directed at a thin gold foil
  • They expected the alpha particles to travel straight through the gold foil with only a small amount of deflection
  • Instead, they discovered that :
    • Most of the alpha particles passed straight through the foil 
    • Some of the alpha particles changed direction but continued through the foil 
    • A few of the alpha particles bounced back off the gold foil 

Alpha Particles Passing Through Atoms in a Gold Foil

rutherford-scattering, IGCSE & GCSE Physics revision notes

When α-particles are fired at thin gold foil most of them pass straight through but a very small number bounce straight back 

  • When α-particles are fired at thin pieces of gold foil:
    • The majority of them go straight through (A)

      This happens because the atom is mainly empty space

    • Some are deflected through small angles (B)

      This happens because the positive α-particles are repelled by the positive nucleus which contains most of its mass

    • A very small number are deflected straight back (C)

      This is because the nucleus is extremely small

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Ann H

Author: Ann H

Expertise: Physics

Ann obtained her Maths and Physics degree from the University of Bath before completing her PGCE in Science and Maths teaching. She spent ten years teaching Maths and Physics to wonderful students from all around the world whilst living in China, Ethiopia and Nepal. Now based in beautiful Devon she is thrilled to be creating awesome Physics resources to make Physics more accessible and understandable for all students no matter their schooling or background.