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Rutherford was born near Nelson in New Zealand. His father was a farmer. Rutherford graduated in mathematics and physics before getting a scholarship to work at the Cavendish laboratory in Cambridge under JJ Thomson.
What did Rutherford do.
Rutherford studied radioactive atoms and he found that they were “unstable”. In that time, people started to understand a bit more about radiation. He had his assistants shoot positive particles at atoms in a thin piece of gold foil to find out where those particles would end up. They could do this because they used a plate which illuminated a little bit when hit by a particle. This did mean they had to do the experiment in the dark. The glow showed that most particles passed through the gold foil unhindered while only a few were diverted slightly to the left or right. When his assistants told Rutherford this disappointing news, he is rumoured to have been so frustrated that he ordered his assistants to position the detecting plates on the other side “for the heck of it”. His assistants did so and were astounded that some of the particles were reflected back from the gold foil. They described it as “Shooting a cannon at a piece of tissue paper and expecting the cannonball to bounce back”. After a lot of calculations, Rutherford concluded that this was only possible if the atom is mostly empty with a small, dense and positively charged nucleus. If the atom was 100 metres wide, the nucleus would have had the size of a pea.
Rutherford’s model of atomic theory
The atom consists mainly of empty space.
The mass of the atom is concentrated in the nucleus, which is a small core at the centre of the atom.
The nucleus contains positive charges.
Electrons move around the nucleus like planets orbiting the sun.
The atom is neutral as it has the same number of positive charges and negatively charged electrons
Assingments
17. Draw an atom of helium according to Rutherford.
18. Explain how Rutherford came to the conclusion that the atom was mostly empty.
19. What is the main difference between the models of Rutherford and Thomson?
20. To the right, there are two drawings of Rutherford’s gold foil experiment. The source of the positive particles at the bottom fires the particles at the foil in the middle. The sphere around it represents the detection plate.
a. In the first drawing: Draw what Rutherford expected to see if Thomson’s mode was correct. (you can decide whether the particles could make it through the positive soup)
b. In the second drawing: Draw what Rutherford actually saw.
For most exercises in this booklet, Rutherford’s model is enough. A positive nucleus with negative electrons in orbit around it. We will describe the shells (and you’ll need it to understand a piece of CSI) but after that you won’t have to worry about the shells again.
After the NT and NG-part, we’ll continue with “the current model of the atom” and for that you must know that the nucleus consists of two different particles: the positive protons and the neutral neutrons
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