Atomics Structure and Theories
- In 1897, J.J.Thompson discovered negatively charged electrons. A few years later, he knew that atoms had a neutral overall charge so he said atoms were like a plum pudding. The main part of the pudding was positive, but there were negatively charged electrons dotted through it. It was nicknamed the “plum pudding model” because it looked similar to a plum pudding.
- A scientist called Ernest Rutherford wanted to see whether the plum pudding theory was correct. So he and two students (Geiger and Marsden) carried out an experiment. The experiment involved firing a narrow beam of alpha particles at a very thin sheet of gold foil in a vacuum. They could see where the alpha particles were hitting and moving to using a detector.
- Most alpha particles passed straight through the foil
- A few particles were deflected
- Very few bounced straight back towards the source
In I/GCSE physics, these results didn’t fit what the expected if the “plum pudding”model was correct. So after reaching conclusions based on their evidence, they came up with their own model of the atom.
Evidence and Conclusions
1.Most alpha particles passed straight through the foil: The atoms in the gold foil contained a lot of empty space
2.Alpha particles are positively charged, when they are deflected back, they must have been deflected by a force of repulsion: The atom must contain a small positively charged centre which we know as the nucleus
3.Alpha particles are heavy, yet some bounced straight back:The nucleus of the atom must be very small but very dense
4.Negative charges didn’t seem to have any effect: This suggested that electrons are not part of the inner atom but orbit the empty space around the nucleus
- Rutherford and Marsden came up with the Nuclear Model of the Atom
- The nucleus contains protons and neutrons. The protons are positively charged and the neutrons are neutral resulting in the nucleus having an overall positive charge.
- The negatively charged electrons orbit in energy shells around the nucleus.
And we're all done for today!
Drafted by Kin (Physics)