AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
The discovery of the electron led to the plum pudding model of the atom.
Full specification wording
The development of the model of the atom (common content with chemistry): The discovery of the electron led to the plum pudding model of the atom.
Thomson's experiments on the rays inside a discharge tube showed the existence of a particle much lighter than any atom and carrying a negative charge, the electron.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 3 of 12
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Thomson's experiments on the rays inside a discharge tube showed the existence of a particle much lighter than any atom and carrying a negative charge, the electron. Two consequences followed at once. First, the atom must contain smaller parts, so it is not indivisible. Second, since ordinary atoms carry no overall charge, something positive must also be present to cancel the electrons. The simplest picture that fitted both facts was a ball of positive charge with the negative electrons dotted through it, which became known as the plum pudding model. It explained neutrality and the existence of electrons, but it placed no concentration of mass or charge anywhere in particular.
What earns the marks
- The electron being identified as a negatively charged particle inside the atom.
- Stating that the atom could therefore no longer be an indivisible sphere.
- Stating that positive charge is needed to balance the negative electrons in a neutral atom.
- Naming the resulting model as the plum pudding model.
Common mistakes and how to put them right
Saying the electron was discovered by the alpha particle scattering experiment.
Describing the plum pudding model as having a nucleus.
Putting the plum pudding model before the discovery of the electron.
Claiming the discovery of the electron showed that the atom is mostly empty space.
Exam tips
- Link the discovery to the model with a because, since that logic is what the question is testing.
- Do not bring in alpha scattering here; it belongs to the next step in the sequence.
- Remember the plum pudding model still had to explain why atoms are neutral overall.
Try the lesson
The start of the The development of the model of the atom (common content with chemistry): The discovery of the electron led to the plum pudding model of the atom. lesson, made from checked teaching notes for this specification point.
Have a go first
Which particle was discovered that led scientists to propose the plum pudding model of the atom?
Listen
Thomson's experiments on the rays inside a discharge tube showed the existence of a particle much lighter than any atom and carrying a negative charge, the electron. Two consequences followed at once. First, the atom must contain smaller parts, so it is not indivisible. Second, since ordinary atoms carry no overall charge, something positive must also be present to cancel the electrons. The simplest picture that fitted both facts was a ball of positive charge with the negative electrons dotted through it, which became known as the plum pudding model. It explained neutrality and the existence of electrons, but it placed no concentration of mass or charge anywhere in particular. A strong answer earns marks for these points. the electron being identified as a negatively charged particle inside the atom. stating that the atom could therefore no longer be an indivisible sphere. stating that positive charge is needed to balance the negative electrons in a neutral atom. naming the resulting model as the plum pudding model. Exam tip: Link the discovery to the model with a because, since that logic is what the question is testing.
See it
Key words
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discovery of the electron
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plum pudding model
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neutral atoms
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divisible atoms
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See every definition
- discovery of the electron
- Thomson's experiments on the rays inside a discharge tube showed a particle much lighter than any atom and carrying a negative charge.
- plum pudding model
- A ball of positive charge with the negative electrons dotted through it, which explained neutrality and the existence of electrons.
- neutral atoms
- Ordinary atoms carry no overall charge, so something positive must also be present to cancel the electrons.
- divisible atoms
- The atom must contain smaller parts, so it is not indivisible.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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