1. 1
   A student compares the electronic structures of a sodium atom and a fluorine atom before they react together. A sodium atom has the electronic configuration 2.8.1 and a fluorine atom has the electronic configuration 2.7. When sodium reacts with fluorine, electrons are transferred from sodium atoms to fluorine atoms to form ions.

   (a)

   What is the charge on the ion formed from a sodium atom?

   [1 mark]

   • A7-
   • B1-
   • C2+
   • D1+

   (b)

   What is the charge on the ion formed from a fluorine atom in this reaction?

   [1 mark]

   • A1+
   • B1-
   • C2-
   • D7+

   (c)

   Explain, in terms of electron transfer, why the sodium and fluorine atoms form ions with the charges you identified in (a) and (b).

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician is preparing magnesium oxide by burning magnesium in oxygen. A magnesium atom has atomic number 12 and mass number 24, and an oxygen atom has atomic number 8 and mass number 16. When they react, each magnesium atom loses two electrons to form an Mg2+ ion, and each oxygen atom gains two electrons to form an O2- ion.

   (a)

   How many electrons are present in one Mg2+ ion?

   [1 mark]

   • A10
   • B12
   • C14
   • D24

   (b)

   An oxygen atom has atomic number 8 and mass number 16. When it reacts with magnesium, each oxygen atom gains two electrons to form an O2- ion. How many electrons are present in one O2- ion?

   [1 mark]

   • A6
   • B8
   • C10
   • D16

   (c)

   Explain how the transfer of electrons between magnesium and oxygen atoms leads to the formation of the ionic compound magnesium oxide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Potassium sulfate is an ionic compound used as a fertiliser. It is made up of potassium ions, K+, and sulfate ions, SO4 2-. Potassium sulfate has a very high melting point and does not conduct electricity when solid, but does conduct electricity when molten or dissolved in water.

   (a)

   Deduce the formula of potassium sulfate, showing how you worked out your answer.

   [3 marks]

   (b)

   Explain, in terms of structure and bonding, why potassium sulfate has a very high melting point but does not conduct electricity when it is solid.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A materials engineer is choosing between sodium chloride (an ionic compound) and a simple molecular covalent substance for an application that requires the material to conduct electricity only when molten or dissolved, and not as a solid. Sodium chloride has a melting point of over 800 degrees Celsius, which is far higher than that of the simple molecular substance being considered.

   (a)

   Explain, in terms of structure and bonding, why solid sodium chloride does not conduct electricity, but molten or dissolved sodium chloride does conduct electricity.

   [6 marks]

   (b)

   Explain, in terms of structure and bonding, why sodium chloride has a melting point of over 800 degrees Celsius, which is far higher than that of the simple molecular covalent substance the engineer is also considering.

   [6 marks]

   Total for question 4: 12 marks

End of questions