A student makes a model of an atom. The model contains 24 electrons, 25 protons and 26 neutrons. Some of these particles are inside a nucleus at the centre of the model. Americium-241 is radioactive. Its nuclide notation is ₂₄₁₉₄Am. Geiger and Marsden studied the structure of gold atoms. Fig. 11.1 shows a version of their apparatus. Alpha-particles strike a thin gold foil. The apparatus shown is in a container from which all the air is removed. Fig. 11.2 shows a model of an atom of the gold foil, with its nucleus at the centre. The alpha-particle labelled A is deflected by the nucleus, as shown. [Figure 11.1] [Figure 11.2 (not to scale)]

1. (a)(i)Determine the nucleon number (mass number) of the atom.[1]
2. (a)(ii)Explain why the model represents a charged atom.[2]
3. (a)(iii)The student makes a new model of a different isotope of the same element. Describe the nucleus of this new model.[2]
4. (b)(i)Determine the number of neutrons in a nucleus of americium-241.[1]
5. (b)(ii)A nucleus of americium-241 emits an α-particle and decays to uranium-237. Complete the nuclear equation for the decay of americium-241. ₂₄₁₉₄Am → ......α + ₂₃⁷₉₂U[3]
6. (c)(i)Suggest why it is necessary to remove all the air from the container.[1]
7. (c)(ii)The alpha-particles are emitted from the source at random. Explain why most of the alpha particles from the source do not reach the gold foil.[1]
8. (c)(iii)On Fig. 11.2, complete the path of the alpha-particle labelled B.[1]
9. (c)(iv)Explain how the alpha-particle scattering experiment provides evidence for the existence of a small nucleus inside the atom.[3]

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