AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The development of the model of the atom (common content with physics): The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea.
By the early 1900s Rutherford's nuclear model was accepted: a tiny positive nucleus surrounded by electrons, but the nucleus seemed too heavy for its charge.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
By the early 1900s Rutherford's nuclear model was accepted: a tiny positive nucleus surrounded by electrons, but the nucleus seemed too heavy for its charge. In 1932 Chadwick bombarded beryllium with alpha particles and detected a penetrating, uncharged radiation. He showed it was a new particle, the neutron, with mass about that of a proton and no charge. Placing neutrons in the nucleus explained the missing mass and the existence of isotopes, which have the same proton number but different mass numbers. This was roughly 20 years after the nucleus became an accepted idea, so the model of the atom developed as new evidence emerged.
What earns the marks
- State that Chadwick's experiments in 1932 provided evidence for a particle in the nucleus with no charge.
- Describe the neutron as having a relative mass of about 1 and a relative charge of 0.
- Explain that neutrons account for the extra mass of the nucleus and for isotopes of an element.
- Link the discovery to the wider development of the atomic model, about 20 years after the nucleus was accepted.
- Use evidence from scattering or radiation experiments to justify a change in the model rather than accepting ideas without evidence.
Common mistakes and how to put them right
Saying Chadwick discovered the electron.
Put it right: The electron was discovered earlier by Thomson, while Chadwick's evidence was for the neutron.
Describing the neutron as positively charged.
Put it right: The neutron is neutral, with relative charge 0.
Claiming the nucleus was unknown until Chadwick's work.
Put it right: The nucleus was accepted about 20 years earlier, and Chadwick added the neutron to the nuclear model.
Exam tips
- Use the phrase 'evidence for' when explaining how experimental results changed the atomic model.
- Quote relative mass and charge values for the neutron to show precise knowledge.
- Link the discovery to isotopes, since this shows why neutrons matter in the model.
Try the lesson
The start of the The development of the model of the atom (common content with physics): The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea. lesson, made from checked teaching notes for this specification point.
Have a go first
Which particle did the experimental work of James Chadwick provide evidence for?
Listen
By the early 1900s Rutherford's nuclear model was accepted: a tiny positive nucleus surrounded by electrons, but the nucleus seemed too heavy for its charge. In 1932 Chadwick bombarded beryllium with alpha particles and detected a penetrating, uncharged radiation. He showed it was a new particle, the neutron, with mass about that of a proton and no charge. Placing neutrons in the nucleus explained the missing mass and the existence of isotopes, which have the same proton number but different mass numbers. This was roughly 20 years after the nucleus became an accepted idea, so the model of the atom developed as new evidence emerged. A strong answer earns marks for these points. State that Chadwick's experiments in 1932 provided evidence for a particle in the nucleus with no charge. Describe the neutron as having a relative mass of about 1 and a relative charge of 0. Explain that neutrons account for the extra mass of the nucleus and for isotopes of an element. Link the discovery to the wider development of the atomic model, about 20 years after the nucleus was accepted. A common slip: Saying Chadwick discovered the electron. Instead, the electron was discovered earlier by Thomson, while Chadwick's evidence was for the neutron. Exam tip: Use the phrase 'evidence for' when explaining how experimental results changed the atomic model.
Key words
Say what each word means before you turn the card.
Development of the atomic model
Try answering aloud or in your head before turning the card.
Experimental evidence and scientific method
Try answering aloud or in your head before turning the card.
Subatomic particles and relative mass and charge
Try answering aloud or in your head before turning the card.
Isotopes and nuclear composition
Try answering aloud or in your head before turning the card.
See every definition
- Development of the atomic model
- The model of the atom changed as new evidence emerged, with the neutron added about 20 years after the nucleus became an accepted idea.
- Experimental evidence and scientific method
- Changes in the model are justified using evidence from experiments rather than accepting ideas without evidence.
- Subatomic particles and relative mass and charge
- The neutron has a relative mass of about 1 and a relative charge of 0.
- Isotopes and nuclear composition
- Isotopes have the same proton number but different mass numbers, and neutrons account for the extra mass of the nucleus and for isotopes.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of The development of the model of the atom (common content with physics): The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge