Radioactivity (6.17)

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

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