AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The development of the model of the atom (common content with physics): The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. This nuclear model replaced the plum pudding model.
In the alpha particle scattering experiment, positively charged alpha particles were fired at thin gold foil.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In the alpha particle scattering experiment, positively charged alpha particles were fired at thin gold foil. Most passed straight through, showing that atoms are mostly empty space. Some were deflected through large angles, and a very few bounced back. A spread-out positive sphere could not produce such strong repulsion, so the positive charge and most of the mass must be concentrated in a tiny central region: the nucleus. Because alpha particles are positive, the repulsion that deflected them shows the nucleus is positively charged. This nuclear model replaced the plum pudding model because it explained the scattering pattern, including the small number of large deflections. The nucleus is very small compared with the atom but contains most of the mass, leaving most of the atom as empty space.
What earns the marks
- Links most alpha particles passing straight through to the conclusion that the atom is mostly empty space.
- Links large-angle deflection or bouncing back of a few alpha particles to a concentrated positive charge and mass at the centre.
- States that the nucleus is positively charged because positive alpha particles are repelled by it.
- Explains that the nuclear model replaced the plum pudding model because the plum pudding model could not explain the deflections.
- Describes the nucleus as tiny compared with the atom but containing most of the atom's mass.
Common mistakes and how to put them right
Saying alpha particles are attracted to the nucleus.
Put it right: Describe repulsion between like charges.
Claiming most alpha particles were deflected.
Put it right: Match each observation to its conclusion carefully.
Stating that the nucleus contains most of the atom's volume.
Put it right: Distinguish mass from volume.
Exam tips
- Answer in pairs: observation first, then the conclusion it supports, for example most pass through, so the atom is mostly empty space.
- Use the word repelled, not attracted, when explaining why positive alpha particles change direction near the nucleus.
- If asked why the model changed, refer to new evidence from the scattering experiment that the old model could not explain.
Try the lesson
The start of the The development of the model of the atom (common content with physics): The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. This nuclear model replaced the plum pudding model. lesson, made from checked teaching notes for this specification point.
Have a go first
In the alpha particle scattering experiment, a small number of alpha particles were deflected by large angles or bounced back. What did this observation lead scientists to conclude about the atom?
Listen
In the alpha particle scattering experiment, positively charged alpha particles were fired at thin gold foil. Most passed straight through, showing that atoms are mostly empty space. Some were deflected through large angles, and a very few bounced back. A spread-out positive sphere could not produce such strong repulsion, so the positive charge and most of the mass must be concentrated in a tiny central region: the nucleus. Because alpha particles are positive, the repulsion that deflected them shows the nucleus is positively charged. This nuclear model replaced the plum pudding model because it explained the scattering pattern, including the small number of large deflections. The nucleus is very small compared with the atom but contains most of the mass, leaving most of the atom as empty space. A strong answer earns marks for these points. Links most alpha particles passing straight through to the conclusion that the atom is mostly empty space. Links large-angle deflection or bouncing back of a few alpha particles to a concentrated positive charge and mass at the centre. States that the nucleus is positively charged because positive alpha particles are repelled by it. Explains that the nuclear model replaced the plum pudding model because the plum pudding model could not explain the deflections. A common slip: Saying alpha particles are attracted to the nucleus: alpha particles and the nucleus are both positive, so the force is repulsion. Instead, describe repulsion between like charges. Exam tip: Answer in pairs: observation first, then the conclusion it supports, for example most pass through, so the atom is mostly empty space.
See it
Key words
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Evidence-driven model replacement
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Concentration of mass and charge in the nucleus
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Empty space within the atom
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Repulsion between like charges
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See every definition
- Evidence-driven model replacement
- The nuclear model replaced the plum pudding model because it explained the scattering pattern, including the small number of large deflections.
- Concentration of mass and charge in the nucleus
- The mass of an atom was concentrated at the centre and the nucleus was charged, so the positive charge and most of the mass must be concentrated in a tiny central region.
- Empty space within the atom
- Most alpha particles passed straight through, showing that atoms are mostly empty space, leaving most of the atom as empty space.
- Repulsion between like charges
- Because alpha particles are positive, the repulsion that deflected them shows the nucleus is positively charged, as a spread-out positive sphere could not produce such strong repulsion.
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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