1. 1
   A science museum is building a large-scale model of a sodium atom, which has 11 protons and 12 neutrons, for its new physics exhibit, and the curator wants to correctly label each part of the model.

   (a)

   A science museum displays a model atom of sodium, which has 11 protons and 12 neutrons. How many electrons does a neutral sodium atom have?

   [1 mark]

   • A11
   • B12
   • C23
   • D1

   (b)

   What is the mass number of this sodium atom?

   [1 mark]

   • A11
   • B12
   • C23
   • D34

   (c)

   The museum model shows the nucleus as a small central sphere with the electrons arranged much further out. Explain why this is a reasonably accurate representation of the relative sizes of the nucleus and the atom as a whole.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A historian of science is writing an article tracing how the model of the atom changed over time, from the plum pudding model through to the alpha particle scattering experiment carried out by Geiger and Marsden, and its interpretation by Rutherford.

   (a)

   A historian of science is researching the plum pudding model of the atom, proposed before the discovery of the nucleus. What did this model suggest about the atom's structure?

   [1 mark]

   • AA tiny positive nucleus surrounded by orbiting electrons
   • BA sphere of positive charge with negative electrons embedded throughout it
   • CElectrons arranged in fixed circular orbits around a nucleus
   • DAn atom made only of neutrons

   (b)

   In the alpha particle scattering experiment, a thin gold foil was bombarded with alpha particles. What observation most surprised the scientists?

   [1 mark]

   • AAll the alpha particles passed straight through with no deflection
   • BThe alpha particles turned into electrons after hitting the foil
   • CAll the alpha particles were absorbed by the foil
   • DA small number of alpha particles were deflected by large angles, some almost straight back

   (c)

   Explain why the result of the alpha particle scattering experiment led scientists to reject the plum pudding model in favour of the nuclear model of the atom.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A hospital physicist is training new radiographers on how atoms interact with electromagnetic radiation during medical imaging, explaining that electrons occupy specific, discrete energy levels, and that these levels change when atoms absorb or emit electromagnetic radiation.

   (a)

   A hospital physicist explains to trainee radiographers that electrons within an atom are arranged at specific, discrete energy levels rather than at any arbitrary distance from the nucleus. Describe what happens to an electron within an atom when the atom absorbs electromagnetic radiation of the correct amount of energy.

   [3 marks]

   (b)

   The hospital physicist then explains what happens when an electron moves from a higher energy level back down to a lower energy level within the atom. Describe this process and state what is emitted as a result, explaining why this matters for medical imaging techniques that rely on detecting emitted electromagnetic radiation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A physics teacher is explaining to a class why the model of the atom has changed several times throughout history, from the indivisible sphere, to the plum pudding model, to the nuclear model, to the Bohr model, and finally to the current model including protons and neutrons.

   (a)

   A physics teacher is explaining to a class why the atomic model changed several times throughout history: from the indivisible sphere, to the plum pudding model, to the nuclear model, to the Bohr model, and finally to the current model including protons and neutrons. Explain, using the alpha particle scattering experiment as a key example, why new experimental evidence can lead scientists to change a previously accepted scientific model, and describe how this specific piece of evidence changed the model of the atom.

   [6 marks]

   (b)

   A student in the class argues that once the nuclear model was accepted, the atomic model should never have needed to change again. Evaluate this claim, explaining why the model of the atom was further developed into the Bohr model and then into the current model, and what this shows about the nature of scientific knowledge.

   [6 marks]

   Total for question 4: 12 marks

End of questions