The nuclear atom and alpha scatteringEdexcel A-Level Physics: Subtopic test

1. 1
   A neutral atom of copper-63 is written ⁶³₂₉Cu.

   (a)

   How many neutrons are there in the nucleus of this atom?

   [1 mark]

   • A29
   • B63
   • C92
   • D34

   (b)

   How many electrons are there in this neutral atom?

   [1 mark]

   • A34
   • B29
   • C63
   • D92

   (c)

   Another isotope of copper has a nucleon number of 65. State the number of protons and the number of neutrons in its nucleus, and explain why it is still copper.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In the Geiger–Marsden experiment a narrow beam of alpha particles in an evacuated chamber was directed at a very thin gold foil. A detector that could be moved round the foil counted the alpha particles scattered at different angles. Most alpha particles passed through the foil with little or no deflection, but a very small number were deflected through large angles.

   (a)

   Which observation shows that most of the volume of an atom is empty space?

   [1 mark]

   • AA very small number of alpha particles were scattered through more than 90°
   • BThe alpha particles carry a positive charge
   • CMost alpha particles passed straight through with little or no deflection
   • DThe alpha particles were emitted at high speed

   (b)

   Why was the apparatus evacuated?

   [1 mark]

   • AAlpha particles would otherwise be absorbed or scattered by air molecules
   • BTo stop the gold foil reacting with oxygen
   • CTo increase the speed of the alpha particles
   • DTo prevent beta particles reaching the detector

   (c)

   Explain why the gold foil had to be very thin.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In one run of an alpha-scattering experiment with a thin gold foil, a total of 4.0 × 10⁵ alpha particles were counted. About 1 in 8000 of them was scattered through an angle of more than 90°.

   (a)

   Calculate the number of alpha particles scattered through more than 90°, and state what such a small fraction shows about the nucleus.

   [3 marks]

   (b)

   Explain how the observations show that the nucleus is positively charged and contains most of the mass of the atom.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Before 1909 the accepted model of the atom was J. J. Thomson's 'plum pudding' model, in which an atom is a sphere of positive charge with the electrons embedded in it. Geiger and Marsden's alpha-scattering results led Rutherford to propose the nuclear model in 1911.

   (a)

   Explain why the results of alpha-scattering could not be explained by the plum pudding model, and how the nuclear model accounts for them.

   [6 marks]

   (b)

   Discuss how the model of the atom has changed over time and why new experimental evidence led scientists to change it.

   [6 marks]

   Total for question 4: 12 marks

End of questions