Radioactivity (6.17)

The atomic model

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Thomson's plum pudding model

  • After the discovery of the electron Thomson proposed that the atom was like a plum pudding with a ball of positive 'dough' with lots of negative electrons stuck inside it.

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Rutherford's nuclear model

  • In 1905, Rutherford directed a beam of alpha particles at a very thin gold film suspended in a vacuum. 
  • Most alpha passed straigh through→ Most of the atom is empty space 
  • Some alpha particles were deflected through quite large angles→ There is a concentration of positive charge in the atom to repel the positively charged alpha particles.
  • A very few alpha particles were repelled back the same way→ The concentration of positive charge must be large enough to cause such deflections (high mass; small volume = dense nucleus)

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Bohr's addition to the model

  • 1913 Bohr suggested the electrons excisted in different energy levels at specific distances from the nucleus
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