1. 1
   A magnesium atom has the electronic structure 2,8,2, describing the number of electrons in each shell starting from the shell nearest the nucleus.

   (a)

   A magnesium atom has the electronic structure 2,8,2, showing the number of electrons in each shell starting from the shell closest to the nucleus. Which rule explains why the first shell contains only 2 electrons before the second shell begins to fill?

   [1 mark]

   • AElectrons occupy the lowest available energy level first
   • BElectrons always spread evenly across all shells at once
   • CElectrons fill the outer shell before the inner shells
   • DElectrons are placed randomly into any shell

   (b)

   What is the maximum number of electrons that the first shell (closest to the nucleus) can hold?

   [1 mark]

   • A18
   • B8
   • C2
   • D1

   (c)

   Explain what the electronic structure 2,8,2 tells you about the arrangement of electrons in a magnesium atom.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chlorine atom has the electronic structure 2,8,7, showing the number of electrons in each of its three shells.

   (a)

   A chlorine atom has the electronic structure 2,8,7. What is the maximum number of electrons that the second shell can hold?

   [1 mark]

   • A7
   • B2
   • C18
   • D8

   (b)

   How many electrons are in the outer shell of a chlorine atom, according to its electronic structure 2,8,7?

   [1 mark]

   • A2
   • B7
   • C8
   • D17

   (c)

   Explain what the electronic structure 2,8,7 shows about the electrons in a chlorine atom.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Neon has the electronic structure 2,8 and sodium has the electronic structure 2,8,1.

   (a)

   State the atomic number of neon and of sodium, and explain how you determined each value from the electronic structures given.

   [3 marks]

   (b)

   Explain why the single outer-shell electron in a sodium atom is more easily removed than an electron from the full outer shell of a neon atom.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student is working out the electronic structures of potassium (atomic number 19) and calcium (atomic number 20), the last two of the first twenty elements.

   (a)

   Explain the rule that electrons occupy the lowest available energy levels, and use this rule to work out and describe the electronic structure of a potassium atom, which has an atomic number of 19.

   [6 marks]

   (b)

   Calcium has an atomic number of 20. Explain, building on the same rule about energy levels, how the electronic structure of calcium is worked out, and compare it with the electronic structure of potassium.

   [6 marks]

   Total for question 4: 12 marks

End of questions