AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
The experimental work of James Chadwick provided the evidence to show the…
Full specification wording
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.
By the early 1930s, the nuclear model explained protons and electrons, but a problem remained: the mass of most atomic nuclei was greater than the mass of their protons alone.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 11 of 14
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
By the early 1930s, the nuclear model explained protons and electrons, but a problem remained: the mass of most atomic nuclei was greater than the mass of their protons alone. About 20 years after the nucleus became an accepted idea, James Chadwick conducted experiments that solved this missing mass problem. His work yielded evidence for a previously undiscovered subatomic particle. He demonstrated that this particle had a relative mass of 1 but carried no electrical charge, leading to the name 'neutron'. Because they are neutral, neutrons were harder to detect. This breakthrough completed the modern nuclear model, establishing that the nucleus contains both protons and neutrons, accounting for the full atomic mass.
What earns the marks
- State that James Chadwick provided the experimental evidence for the existence of neutrons.
- Explain that neutrons are located within the central nucleus of an atom.
- Identify that the discovery of the neutron explained the missing mass of atomic nuclei.
- State that neutrons have a relative charge of 0 and a relative mass of 1.
- Recognise that Chadwick's discovery occurred about 20 years after the nucleus was first accepted as a scientific idea.
Common mistakes and how to put them right
Claiming that Chadwick discovered the electron.
Put it right by stating that Chadwick discovered the neutron, while J.J. Thomson discovered the electron.
Saying that neutrons are positively charged.
Put it right by stating that neutrons have no electrical charge (they are neutral), whereas protons are positive.
Stating that neutrons orbit the nucleus.
Put it right by placing neutrons inside the dense central nucleus alongside protons.
Exam tips
- You do not need to describe the specific details of Chadwick's experiments, but you must know that his experimental work provided the evidence for neutrons.
- Remember the timeline: the neutron was discovered approximately 20 years after the nucleus became an accepted scientific idea, completing the modern atomic 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. lesson, made from checked teaching notes for this specification point.
Have a go first
Whose experimental work provided the evidence for the existence of neutrons within the nucleus?
Listen
By the early 1930s, the nuclear model explained protons and electrons, but a problem remained: the mass of most atomic nuclei was greater than the mass of their protons alone. About 20 years after the nucleus became an accepted idea, James Chadwick conducted experiments that solved this missing mass problem. His work yielded evidence for a previously undiscovered subatomic particle. He demonstrated that this particle had a relative mass of 1 but carried no electrical charge, leading to the name 'neutron'. Because they are neutral, neutrons were harder to detect. This breakthrough completed the modern nuclear model, establishing that the nucleus contains both protons and neutrons, accounting for the full atomic mass. A strong answer earns marks for these points. State that James Chadwick provided the experimental evidence for the existence of neutrons. Explain that neutrons are located within the central nucleus of an atom. Identify that the discovery of the neutron explained the missing mass of atomic nuclei. State that neutrons have a relative charge of 0 and a relative mass of 1. A common slip: Claiming that Chadwick discovered the electron. Instead, stating that Chadwick discovered the neutron, while J.J. Thomson discovered the electron. Exam tip: You do not need to describe the specific details of Chadwick's experiments, but you must know that his experimental work provided the evidence for neutrons.
Key words
Say what each word means before you turn the card.
Discovery of the neutron
Try answering aloud or in your head before turning the card.
Structure of the nucleus
Try answering aloud or in your head before turning the card.
Development of the atomic model
Try answering aloud or in your head before turning the card.
See every definition
- Discovery of the neutron
- James Chadwick conducted experiments that yielded evidence for a previously undiscovered subatomic particle, which had a relative mass of 1 but carried no electrical charge.
- Structure of the nucleus
- The modern nuclear model establishes that the nucleus contains both protons and neutrons, accounting for the full atomic mass.
- Development of the atomic model
- This breakthrough completed the modern nuclear model, about 20 years after the nucleus became an accepted idea.
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.
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