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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Describe the plum pudding model of the atom.
A ball of positive charge with negative electrons embedded in it.
Niels Bohr adapted the nuclear model of the atom. What did Bohr suggest about the electrons?
The electrons orbit the nucleus at specific distances.
Later experiments showed that the positive charge of a nucleus could be subdivided into a whole number of smaller particles, each with the same charge. What name was given to these particles?
Protons
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) Before the electron was discovered, what did scientists think atoms were like? Tick (✓) one box.[1]
Tiny spheres that could not be divided
Balls of positive charge with electrons embedded in them
Tiny positive nuclei with electrons orbiting them
Nuclei containing protons and neutrons
(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]
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
Question 2Medium5 marks
The results of the alpha particle scattering experiment led to the plum pudding model of the atom being replaced by the nuclear model.
(a) Give two differences between the plum pudding model and the nuclear model of the atom.[2]
(b) Explain why the plum pudding model had to be replaced.[2]
(c) Later experiments showed that the positive charge of a nucleus could be subdivided into a whole number of smaller particles, each with the same charge. What name was given to these particles?[1]
Show the answer and mark scheme
(a)Answer: In the nuclear model the mass and the positive charge are concentrated in a tiny central nucleus and most of the atom is empty space; in the plum pudding model they are spread through the whole atom.
nuclear model: mass concentrated in the nucleus; plum pudding: mass spread throughout the atom
nuclear model: positive charge concentrated in the nucleus; plum pudding: positive charge spread throughout the atom
nuclear model: the atom is mostly empty space; plum pudding: no empty space (a solid ball)
nuclear model: electrons outside the nucleus / in orbits; plum pudding: electrons embedded in the ball of positive charge
(b)Answer: The new evidence (large deflections and alpha particles bouncing back) could not be explained by the plum pudding model.
the scattering experiment gave new (experimental) evidence / results that the plum pudding model could not explain
(for example) some alpha particles were deflected through large angles / bounced back, which needs a small, concentrated nucleus
(c)Answer: Protons
protons
Question 3Hard8 marks
In 1909, scientists fired alpha particles at a very thin sheet of gold foil in a vacuum. At the time, most scientists accepted the plum pudding model of the atom.
(a) Explain how the results of the alpha particle scattering experiment led to the plum pudding model being replaced by the nuclear model of the atom.[6]
(b) Suggest why the experiment was done in a vacuum.[1]
(c) Suggest why the gold foil was very thin.[1]
Show the answer and mark scheme
(a)Answer: The plum pudding model predicted almost no deflection. Most alpha particles went straight through (mostly empty space), some were deflected (concentrated positive charge) and a few bounced back (mass concentrated in a tiny nucleus). The old model could not explain this, so it was replaced by the nuclear model.
alpha particles are positively charged (and are fired at thin gold foil)
the plum pudding model has its positive charge and mass spread out, so all the alpha particles were expected to pass through with little or no deflection
most alpha particles passed straight through, so the atom must be mostly empty space
some alpha particles were deflected, so there must be a concentrated region of positive charge that repels them
a very small number bounced back, so the mass (and charge) must be concentrated in a very small central nucleus
the plum pudding model could not explain the large deflections / the alpha particles that bounced back
so the new evidence led to the nuclear model: a tiny, positively charged nucleus containing most of the mass, surrounded by electrons
new experimental evidence can lead to a scientific model being changed or replaced
Marked with levels of response: the full level descriptors are in the app.
(b)Answer: Alpha particles would be stopped by just a few centimetres of air.
alpha particles have a short range in air / would be absorbed (stopped) by the air
(c)Answer: So that the alpha particles could pass through, with each one passing only a few layers of atoms.
so that the alpha particles could pass through it / were not absorbed by the foil / each alpha particle passed only a few atoms