Suggest — 4 marks
In 1909, Ernest Rutherford's team conducted the famous gold foil experiment. They fired alpha particles at a thin sheet of gold foil and observed how the particles were deflected. Most alpha particles passed straight through with little deflection, but some were deflected at large angles, and a few even bounced backwards. This experiment provided crucial evidence that challenged the existing 'plum pudding' model of the atom.
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(a) Suggest why most alpha particles passed straight through the gold foil with little or no deflection.
[1 mark]
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(b) Suggest why some alpha particles were deflected at large angles or bounced backwards.
[2 marks]
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(c) Suggest how Rutherford's observations from this experiment led to the development of the nuclear model of the atom, rather than supporting the plum pudding model.
[1 mark]
Show mark scheme
- (a) Most of the atom is empty space / atoms contain mostly empty space
- (b) Alpha particles were deflected when they came close to / collided with the nucleus
- (b) The nucleus is positively charged and repelled the positively charged alpha particles
- (c) The plum pudding model predicted the positive charge was distributed evenly throughout the atom, which would not cause large deflections; the observations showed charge is concentrated in a small nucleus at the centre
Calculate — 4 marks
A scientist is studying the structure of atoms using experimental data. She observes that an atom of carbon has 6 protons in its nucleus. She needs to determine information about the atomic structure and compare it with another element.
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(a) A carbon atom has a mass number of 12 and an atomic number of 6. Calculate the number of neutrons in a carbon atom.
[1 mark]
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(b) An oxygen atom has an atomic number of 8 and a mass number of 16. Calculate the number of neutrons in an oxygen atom.
[1 mark]
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(c) Calculate the total number of electrons in 2 carbon atoms (atomic number 6). Assume the atoms are neutral.
[2 marks]
Show mark scheme
- (a) Number of neutrons = mass number − atomic number = 12 − 6 = 6 neutrons (1 mark for correct calculation and answer)
- (b) Number of neutrons = mass number − atomic number = 16 − 8 = 8 neutrons (1 mark for correct calculation and answer)
- (c) In a neutral atom, number of electrons = atomic number = 6 electrons per carbon atom (1 mark)
- (c) Total electrons in 2 carbon atoms = 6 × 2 = 12 electrons (1 mark for correct final answer)
Evaluate — 3 marks
Scientists in the early 20th century debated the structure of the atom. Rutherford's nuclear model (1911) replaced Thomson's plum pudding model after the gold foil experiment. However, Rutherford's model had a significant theoretical problem: according to classical physics, electrons orbiting the nucleus should continuously emit electromagnetic radiation, lose energy, and spiral into the nucleus in a fraction of a second. This prediction contradicted experimental observations that atoms are stable.
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(a) Identify one piece of experimental evidence from the gold foil experiment that contradicted Thomson's plum pudding model.
[1 mark]
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(b) Evaluate how effective Rutherford's nuclear model was at explaining atomic structure, considering both its strengths and limitations.
[2 marks]
Show mark scheme
- (a) Most alpha particles passed straight through the foil (or: very few were deflected/bounced back) - contradicting the uniform distribution of charge in Thomson's model / showing charge is concentrated in a small region
- (b) Strength: Rutherford's model correctly explained the gold foil experiment results / correctly identified that atoms contain a concentrated positive nucleus / explained why most particles pass through
- (b) Limitation: The model could not explain atomic stability / could not explain why electrons do not spiral into the nucleus / classical physics predicted atoms should collapse but they don't / the model did not account for quantised electron orbits (or: Bohr's later refinements were needed)
Explain — 3 marks
Scientists have used different experimental techniques to understand atomic structure. In the early 1900s, Ernest Rutherford conducted the famous gold foil experiment where alpha particles were fired at thin gold foil. Most particles passed straight through, but some were deflected at large angles, and a few bounced straight back. This experiment was crucial in developing our modern model of the atom.
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(a) Explain why Rutherford's results contradicted the plum pudding model of the atom.
[1 mark]
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(b) Explain how Rutherford's observations of alpha particles bouncing back from the gold foil led to the conclusion that most of the atom's mass is concentrated in a small nucleus.
[2 marks]
Show mark scheme
- (a) The plum pudding model predicted alpha particles would pass through with minimal deflection because positive charge was spread throughout the atom / the model could not explain why some alpha particles were deflected at large angles or bounced back
- (b) Alpha particles that bounced back must have encountered a very strong repulsive force, indicating a concentrated positive charge in a small region
- (b) If the positive charge were spread out (as in plum pudding model), the deflecting force would be weak and particles would not bounce back at large angles; the fact that most particles passed through shows the atom is mostly empty space with a small dense nucleus containing most of the mass
Describe — 5 marks
Scientists in the early 20th century used alpha particle scattering experiments to investigate the structure of atoms. Ernest Rutherford's team fired alpha particles at a thin gold foil and observed how the particles were deflected. This experiment led to significant changes in our understanding of atomic structure.
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(a) Describe how the results of the alpha particle scattering experiment contradicted the plum pudding model of the atom.
[2 marks]
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(b) Describe the nuclear model of the atom that Rutherford proposed based on the scattering results.
[2 marks]
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(c) Describe one limitation of Rutherford's nuclear model that was later addressed by the Bohr model of the atom.
[1 mark]
Show mark scheme
- (a) The plum pudding model predicted that alpha particles would pass straight through (or be slightly deflected) as the positive charge was spread throughout the atom
- (a) However, some alpha particles were deflected at large angles / some bounced back, showing that the positive charge must be concentrated in a small region
- (b) The atom has a small, dense, positively charged nucleus at the centre
- (b) Electrons orbit the nucleus / electrons surround the nucleus at a distance
- (c) Rutherford's model did not explain why electrons don't spiral into the nucleus / did not explain the stability of atoms, OR Rutherford's model did not explain the discrete energy levels / line spectra of elements (accept: Bohr proposed electrons occupy fixed orbits/energy levels at specific distances)
GCSE Perfect