Atomic structure and alpha scatteringEdexcel International A Level Physics: Subtopic test

1. 1
   Copper has two stable forms of atom, copper-63 and copper-65. The nuclide notation for copper-63 is $^{63}_{29}\mathrm{Cu}$.

   (a)

   How many neutrons are there in a nucleus of copper-65?

   [1 mark]

   • A29
   • B65
   • C94
   • D36

   (b)

   Which statement correctly describes the difference between a copper-65 nucleus and a copper-63 nucleus?

   [1 mark]

   • ACopper-65 has two more neutrons
   • BCopper-65 has two more protons
   • CCopper-65 has two more electrons in a neutral atom
   • DCopper-65 has a larger proton number

   (c)

   Explain why atoms of copper-63 and copper-65 have the same chemical properties but different masses.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In 1909 Geiger and Marsden directed a narrow beam of alpha particles at a very thin gold foil inside an evacuated chamber. A detector was moved around the foil to count the alpha particles scattered through different angles.

   (a)

   The chamber was evacuated because

   [1 mark]

   • Aalpha particles would otherwise be repelled by the oxygen nuclei
   • Balpha particles would otherwise be absorbed or scattered by air molecules
   • Cthe gold foil would otherwise react with the air
   • Da vacuum increases the speed of the alpha particles

   (b)

   Most of the alpha particles passed straight through the foil with little or no deflection. This observation suggests that

   [1 mark]

   • Athe nucleus of an atom is negatively charged
   • Batoms are solid spheres of uniform density
   • Cmost of the volume of an atom is empty space
   • Dthe electrons have a greater mass than the alpha particles

   (c)

   A very small number of alpha particles were scattered through angles greater than 90°. Explain what this shows about the structure of the atom.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a repeat of the alpha particle scattering experiment, 2.4 × 10⁵ alpha particles are incident on a thin gold foil. About 1 in 8000 of the alpha particles is deflected through an angle greater than 90°. Before this experiment the plum pudding model proposed by J. J. Thomson was the accepted model of the atom.

   (a)

   Calculate the number of alpha particles deflected through more than 90°, and state what the result shows about the size of the nucleus compared with the atom.

   [3 marks]

   (b)

   Explain why the results of the experiment could be explained by the nuclear model but not by the plum pudding model.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Models of the atom have been revised several times. Thomson's plum pudding model (after the discovery of the electron in 1897) was replaced by Rutherford's nuclear model in 1911, following the work of Geiger and Marsden. The model was developed further by Bohr in 1913 and by the discovery of the neutron by Chadwick in 1932.

   (a)

   Describe the observations made in the alpha particle scattering experiment and explain how each one led Rutherford to the nuclear model of the atom.

   [6 marks]

   (b)

   Discuss how our understanding of atomic structure has changed over time, explaining why each model was replaced or developed.

   [6 marks]

   Total for question 4: 12 marks

End of questions