AQA GCSE Chemistry (8462), Higher tier · Atomic structure and the periodic table › Atoms, isotopes and electronic structure
Practise Development of the model of the atom. 14 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Scientists' ideas about atoms have changed over time. Describe the plum pudding model of the atom.
A ball of positive charge with negative electrons embedded in it.
Experiments showed that the positive charge of a nucleus can be divided into a whole number of smaller particles. Each particle has the same amount of positive charge. What name was given to these particles?
protons
In 1897, J. J. Thomson investigated the particles given off by electrical discharge tubes. He found that the particles:
had a mass more than 1000 times smaller than the mass of a hydrogen atom, the lightest atom
had a negative charge
were the same whichever gas was inside the tube.
Name the particle that Thomson discovered.
electron
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Scientists' ideas about atoms have changed over time.
(a) Which statement describes the model of the atom that scientists used before the plum pudding model? Tick (✓) one box.[1]
Tiny spheres that could not be divided
Particles made of protons, neutrons and electrons
Nuclei with electrons orbiting at fixed distances
Mostly empty space with a tiny nucleus
(b) The discovery of which particle led to the plum pudding model of the atom? Tick (✓) one box.[1]
Alpha particle
Electron
Neutron
Proton
(c) Describe the plum pudding model of the atom.[2]
(d) Name the scientist whose experimental work provided evidence for neutrons.[1]
Show the answer and mark scheme
(a)Answer: Tiny spheres that could not be divided
(b)Answer: Electron
(c)Answer: A ball of positive charge with negative electrons embedded in it.
a ball / sphere of positive charge
with (negative) electrons embedded in it / scattered through it
(d)Answer: (James) Chadwick
(James) Chadwick
Question 2Medium6 marks
In the alpha particle scattering experiment, positively charged alpha particles were fired at a very thin sheet of gold.
(a) Most of the alpha particles passed straight through the gold. What does this show about atoms?[1]
(b) A very small number of alpha particles bounced back towards the source. Explain what this shows about the nucleus of an atom.[3]
(c) Explain why these results could not be explained by the plum pudding model.[2]
Show the answer and mark scheme
(a)Answer: Most of an atom is empty space.
most of the atom is empty space
(b)Answer: The nucleus is positively charged (it repels the alpha particles), it contains most of the mass of the atom, and it is very small.
the nucleus is positively charged so it repels the (positive) alpha particles
most of the mass of the atom is concentrated in the nucleus
the nucleus is very small compared with the atom (because very few alpha particles bounced back)
the nucleus is at the centre of the atom
(c)Answer: In the plum pudding model the positive charge and mass are spread out, so the alpha particles would all pass through with little or no deflection.
(in the plum pudding model) the positive charge / mass is spread out through the atom
so the alpha particles would (all) pass through with little or no deflection / none would bounce back
Question 3Hard6 marks
The model of the atom has been changed several times as new evidence was found.
Describe how the model of the atom has developed from the idea of tiny spheres that could not be divided to the nuclear model with protons, neutrons and electrons. Include the evidence that led to each change.[6]
Show the answer and mark scheme
Answer: Indivisible spheres → electron discovered → plum pudding model → alpha scattering → nuclear model → Bohr's electron orbits → protons → Chadwick's neutrons; each change followed new evidence.
atoms were first thought to be tiny spheres that could not be divided (e.g. Dalton)
the discovery of the electron led to the plum pudding model
plum pudding model: a ball of positive charge with negative electrons embedded in it
alpha particle scattering: most alpha particles passed straight through, so the atom is mostly empty space
a few alpha particles were deflected or bounced back, so mass and positive charge are concentrated in a tiny nucleus
the nuclear model replaced the plum pudding model
Bohr suggested electrons orbit the nucleus at specific distances; his calculations agreed with experimental observations
later experiments showed the positive charge of the nucleus is made of whole numbers of protons
Chadwick's experimental work provided evidence for neutrons in the nucleus (about 20 years after the nucleus was accepted)
Marked with levels of response: the full level descriptors are in the app.