1. 1
   A museum curator is designing a timeline display about how scientific ideas of the atom changed over time. The display begins with the earliest idea, that atoms are tiny, solid, indivisible spheres, before moving on to describe the discovery of the electron and later models.

   (a)

   A museum curator is writing a timeline display about scientific ideas of the atom. Before the discovery of the electron in 1897, scientists such as John Dalton pictured atoms as tiny, solid spheres that could not be divided into smaller parts.
   
   What is this earliest model of the atom called?

   [1 mark]

   • AThe solid sphere model
   • BThe nuclear model
   • CThe plum pudding model
   • DBohr's model

   (b)

   The next panel of the museum display explains that, after J. J. Thomson discovered the electron, scientists proposed a new model in which negatively charged electrons were embedded within a sphere of positive charge.
   
   What is this model of the atom called?

   [1 mark]

   • AThe solid sphere model
   • BThe nuclear model
   • CThe plum pudding model
   • DThe shell model

   (c)

   Explain how the discovery of the electron led scientists to change their model of the atom from the solid sphere model to the plum pudding model.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A physics documentary is recreating Ernest Rutherford's alpha particle scattering experiment, in which positively charged alpha particles were fired at a very thin sheet of gold foil. Most particles passed straight through, some were deflected at large angles, and a very small number bounced almost straight back towards the source.

   (a)

   What did the small number of alpha particles that bounced back suggest about the structure of the atom?

   [1 mark]

   • AMost of an atom's mass and positive charge is concentrated in a tiny, dense nucleus
   • BThe atom is mostly empty space with a large, positively charged nucleus
   • CElectrons are embedded throughout a sphere of positive charge
   • DAtoms are indivisible, solid spheres

   (b)

   What did the fact that most alpha particles passed straight through the gold foil undeflected suggest about the structure of the atom?

   [1 mark]

   • AThe atom is a uniform, solid sphere with no internal structure
   • BThe atom is mostly empty space
   • CAll of the atom's mass is spread evenly throughout its volume
   • DThe nucleus fills almost the entire volume of the atom

   (c)

   Explain why the results of the alpha particle scattering experiment led scientists to replace the plum pudding model with the nuclear model of the atom.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A science historian is writing a biography of Niels Bohr, describing how he adapted the nuclear model of the atom by proposing that electrons orbit the nucleus only at specific, fixed distances (energy levels), rather than moving freely around it.

   (a)

   A science historian is writing a biography of Niels Bohr. She explains that, after the nuclear model was proposed, Bohr adapted it by suggesting that electrons orbit the nucleus only at specific, fixed distances, rather than moving freely around it. Describe what problem Bohr's model solved, how his model differed from the nuclear model that came before it, and why scientists accepted it.

   [3 marks]

   (b)

   The historian also describes how, after Bohr's model was accepted, further experimental work led scientists to identify the existence of protons and, later, neutrons within the nucleus. Describe how this discovery further refined the model of the atom, and state the relative charges of the proton, neutron and electron.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A science communicator is producing a video explaining the full historical journey of the model of the atom, from the earliest solid sphere model to the model used today, and the experimental evidence behind each change.

   (a)

   Describe, in order, each major model of the atom, the key experimental evidence or discovery that led to each change, and what each new model added or corrected compared with the one before it.

   [6 marks]

   (b)

   The science communicator wants to end the video by explaining why scientific models like the atomic model change over time, using the history of the atomic model as her main example. Evaluate the role that experimental evidence played in changing the atomic model, and explain why scientists were willing to abandon models that had previously been accepted.

   [6 marks]

   Total for question 4: 12 marks

End of questions