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GCSE Questions: Nuclear Structure

Q2. Over 100 years ago, scientists thought the atom was like a 'plum pudding'. The diagram shows the plum pudding model of the atom.

(a) The scientists knew that an atom has negatively charged particles. They also knew that an atom has no overall charge.

What did the scientists conclude about the charge on the 'pudding part' of the atom?

That it must have an equal amount of positive charge to cancel out the sum of the negative charge from the negatively charged particles.

[1 mark]

(b) Two scientists named Rutherford and Marsden devised an experiment to investigate the plum pudding model of the atom.

The experiment involved firing alpha particles at a thin sheet of gold. The scientists measured how many of the alpha particles were scattered.

Using the plum pudding model, the scientists predicted that only a few of the alpha particles would be scattered by more than 4°.

Over several months, more than 100 000 measurements were made.

(i) The results from this experiment caused the plum pudding model to be replaced by a new model of the atom. Explain why.

As if the plum pudding model was correct it was expected that the alpha particles would go straight through, only slightly deflected from their path. But a significant number of alpha particles were scattered by more than 4o and alpha particles were even deflected backwards (back-scattered) , these results could not be explained by 'plum pudding' model.

[2 marks]

(ii) Suggest one reason why other scientists thought this experiment provided valid evidence for a new model of the atom.

Many/(over)100 000 measurements/results taken over several months

OR Rutherford(and Marsden) were respected scientists

Just saying 'the experiment was repeated many times' was insufficient to get you the mark.

[1 mark]

(c) Describe the model now used for the structure of an atom.

In your answer you should:

give details of the individual particles that make up an atom

include the relative masses and relative charges of these particles.

Do not include a diagram in your answer.

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 3:

A more detailed description is given, naming the particles and polarity of charge

and

either the relative mass is given for at least two particles

or the relative charge is given for at least two particles
5 - 6 marks
Level 2:

A description is given with all three particles named

and

either the polarity of charge associated with the three particles

or the relative mass of the three particles

or the relative mass for one particle and the relative charge for one particle given
3 - 4 marks
Level 1:

A brief description is given with some particles correctly named.
1 - 2 marks
Level 0:

No relevant information
0 marks

 

Examples of physics points that should be made in the response:

Brief description

contains protons, neutrons and electrons

protons are positive

electrons are negative

neutrons are uncharged

has a nucleus

relative charge: proton +1; electron – 1; neutron 0

relative mass: proton 1; neutron 1; electron (about) 1/2000

More detailed description

protons and neutrons make up the nucleus

electrons orbit the nucleus

electrons are in shells

most of the atom is empty space

nucleus occupies a very small fraction of the volume of the atom

electrons orbit at a relatively large distance from the nucleus

most of the mass of the atom is contained in the nucleus

the nucleus as a whole is positively charged

total number of protons in the nucleus equals the total number of electrons orbitting it in an atom

[6 marks]

(Total 10 marks)