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Year 11
OCR
Higher

Evidence of atomic structure

I can describe how alpha particles were used to show the size and nature of atomic nuclei.

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New
New
Year 11
OCR
Higher

Evidence of atomic structure

I can describe how alpha particles were used to show the size and nature of atomic nuclei.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. Background radiation is caused by unstable nuclei that are around us all of the time.
  2. Atoms are very small with a radius of about 1 × 10⁻¹⁰ m.
  3. The alpha particle scattering experiment (Rutherford, 1909) provides evidence for the size and nature of atomic nuclei.
  4. An atomic nucleus has a radius about 10 000 times smaller than that of an atom.
  5. Most of the mass of an atom is in its nucleus.

Common misconception

Atoms are visible under powerful optical microscopes.

Emphasise that atoms are far too small to see and our descriptions of atoms are models, based on evidence, that help us understand how they behave.

Keywords

  • Background radiation - the radiation in the surroundings of a particular place

  • Alpha particle - a small, positively charged particle which was used to discover the nucleus

  • Alpha scattering experiment - the experiment used to discover the atomic nucleus from the deflection of alpha particles fired at it

  • Nucleus - the central part of an atom which contains most of the mass and all of the positive charge

Set up a GM tube and counter to run as pupils enter the lesson and use a variety of materials to show that background radiation is emitted from many natural and human–made sources (brazil nuts, bananas, piece of granite, alpha source from radioactivity kit).
Teacher tip

Content guidance

  • Depiction or discussion of violence or suffering

Supervision

Adult supervision recommended

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.
What happens to the particles in a liquid when its temperature increases?
They expand to take up more space.
They contract and take up less space.
Correct answer: Their size does not change.
Correct answer: Their average speed increases.
Their average speed decreases.
Q2.
What is the smallest component of an element?
a gas
a molecule
Correct answer: an atom
a crystal
a mole
Q3.
Which of these are elements?
Correct answer: gold (Au)
carbon dioxide (CO$$_2$$)
Correct answer: oxygen (O$$_2$$)
hydrochloric acid (H$$_2$$SO$$_4$$)
Correct answer: uranium (U)
Q4.
In which state are the particles in a substance most free to move around?
solution
solid
liquid
Correct answer: gas
crystal
Q5.
Match the particles to their descriptions.
Correct Answer:electron,negatively charged particle found outside a nucleus

negatively charged particle found outside a nucleus

Correct Answer:proton,positively charges particle found in a nucleus

positively charges particle found in a nucleus

Correct Answer:neutron,particle with no charge found in a nucleus

particle with no charge found in a nucleus

Correct Answer:atom,neutral particle

neutral particle

Q6.
Starting with the largest, put these objects in order of mass.
1 - a 1 kg block of gold
2 - a gold ring
3 - a single gold atom
4 - a single proton
5 - a single electron

Exit quiz

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6 Questions

Q1.
Match each of the following terms used in nuclear physics to the correct definitions.
Correct Answer:background radiation,the radiation in the surroundings at a particular place

the radiation in the surroundings at a particular place

Correct Answer:alpha particle,a positively charged particle that is a type of radiation

a positively charged particle that is a type of radiation

Correct Answer:alpha scattering experiment,an investigation to explore the structure of atoms

an investigation to explore the structure of atoms

Correct Answer:nucleus,the part in the middle of an atom which contains most of its mass

the part in the middle of an atom which contains most of its mass

Q2.
Which of the following are properties of an alpha particle?
Correct answer: It has positive electrical charge.
It has negative electrical charge.
It is uncharged (neutral).
Correct answer: It is a particle with a mass similar to a helium atom.
It is high frequency electromagnetic radiation.
Q3.
Which of the following are classified as artificial sources of background radiation?
rocks
Correct answer: nuclear fallout from weapons tests
cosmic rays
brazil nuts
Correct answer: nuclear waste from power stations
Q4.
Match the results of the alpha particle scattering experiment (where a beam of alpha particles is fired at gold foil) to the corresponding conclusions made.
Correct Answer:most pass straight through,most of an atom is empty space

most of an atom is empty space

Correct Answer:some are deflected by large angles,there is a nucleus with a positive charge

there is a nucleus with a positive charge

Correct Answer:a small number ‘bounce back’,the nucleus contains most of the mass of the atom

the nucleus contains most of the mass of the atom

Q5.
Starting with the earliest, sort the following into date order.
1 - model of atoms as small, solid spheres
2 - discovery of the electron and use of ‘plum pudding’ atomic model (Thomson)
3 - discovery of the nucleus using alpha particle scattering experiment (Rutherford)
4 - electron shell model developed (Bohr)
5 - discovery of neutrons in nucleus (Chadwick)
Q6.
Henri Becquerel discovered radiation in 1896 when investigating uranium salts. What properties did the radiation have that lead to the discovery?
It was an artificial substance.
Correct answer: It could pass through paper.
It caused objects to glow in the dark.
Correct answer: Exposed photographic film was made darker.
It made him ill.