1. 1
   A physics teacher uses a helium atom as an example to explain atomic structure to a class, describing a tiny central region surrounded by orbiting particles.

   (a)

   A physics teacher explains that a helium atom consists of a tiny central region surrounded by particles in orbit around it. What is the correct description of the atom's structure?

   [1 mark]

   • AA positively charged nucleus surrounded by negatively charged electrons in orbit
   • BA negatively charged nucleus surrounded by positively charged electrons in orbit
   • CA neutral nucleus surrounded by neutral particles
   • DA positively charged nucleus with no surrounding particles

   (b)

   An atom can become a positive ion. What process causes an atom to become a positive ion?

   [1 mark]

   • AGaining one or more electrons
   • BLosing one or more electrons
   • CLosing one or more protons
   • DGaining one or more neutrons

   (c)

   State the relative electric charges of a proton, a neutron and an electron.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a museum exhibit recreating a famous historical experiment, a beam of alpha particles is directed at a very thin sheet of gold foil in an evacuated chamber, and a detector records the angles at which the alpha particles are scattered.

   (a)

   A small fraction of the alpha particles are observed to bounce almost straight back from the foil. What does this observation provide evidence for?

   [1 mark]

   • AElectrons are located inside the nucleus
   • BThe atom is a uniform sphere of positive charge with no concentrated centre
   • CThe nucleus contains most of the mass of the atom and is positively charged
   • DThe nucleus is negatively charged

   (b)

   The exhibit also shows that the vast majority of alpha particles pass straight through the gold foil with little or no deflection. What does this observation suggest about the structure of the gold atoms?

   [1 mark]

   • AAlpha particles have no charge
   • BThe nucleus fills almost the entire volume of the atom
   • CGold atoms contain no electrons
   • DMost of the atom is empty space

   (c)

   State two further conclusions about the structure of the atom, other than the size of the nucleus and the amount of empty space, that can be drawn from the pattern of scattering of alpha particles by the gold foil.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A chemistry teacher explains to students that a neutral sodium atom can lose an electron to become a sodium ion, a process that is important in the formation of table salt.

   (a)

   Describe, in terms of protons and electrons, why the sodium atom is neutral before losing the electron, and explain why the resulting ion is positively charged.

   [3 marks]

   (b)

   A different student in the class asks whether a chlorine atom could instead become a negative ion. Explain, in terms of protons and electrons, how a neutral chlorine atom could become a negatively charged ion, and state what must be true about the numbers of protons and electrons for this to happen.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A science documentary explains how our understanding of the structure of the atom developed following a historic alpha-particle scattering experiment using thin gold foil.

   (a)

   Describe the nuclear model of the atom that resulted from this experiment, including the evidence provided by each of the three main observations made (particles passing straight through, particles deflected through small angles, and particles bouncing almost straight back), and explain what each observation reveals about the atom's structure.

   [6 marks]

   (b)

   The documentary then explains how the number of protons and neutrons in the nucleus, together with the concept of isotopes, are represented using nuclide notation. Explain what is meant by proton number and nucleon number, describe what an isotope is, and explain how nuclide notation is used to represent an atom, using a worked example of an atom of your choice to illustrate how the number of neutrons can be calculated.

   [6 marks]

   Total for question 4: 12 marks

End of questions