AQA GCSE Discovering the Proton and Neutron

AQA GCSE Discovery of the Proton and Neutron

Nucleus

At the time the structure of the nucleus was unknown, so it was treated as a positively charged sphere, its exact structure was discovered later. 

Discovery of the proton

Ernest Rutherford discovered the proton.

Around 1917 he bombarded nitrogen nuclei with alpha particles and this led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles.

Each particle having the same amount of positive charge. The name proton was given to these particles.

Discovery of the Neutron

James Chadwick carried out experimental work to prove the existence of neutrons. This was around 1932, 20 years after the discovery of the nuclear model.

Scientists knew that the mass of a hydrogen nucleus was 1 and its charge was +1 because it contained 1 proton. 

Then they looked at other nuclei and the mass was always bigger than the positive charge.

A Lithium  nucleus has a mass of 7, but a total positive charge of +3 due to 3 protons. So, another particle was causing this extra mass that had no charge!

This other particle was the neutron!

James Chadwick discovered that the neutron has no charge, but its mass is similar to that of a proton. 

As a result the nuclear model was changed again to look like what we know today

 

Structure of the atom

Practice Questions

1.Describe how the idea of protons came about

2.Describe how scientists knew that there were particles other than protons in the nucleus?

 

3. Which famous Scientist discovered the neutron?

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