Physical properties of Period 3 elementsAQA A-Level Chemistry: Subtopic test

1. 1
   The atomic radius of the elements decreases across Period 3, from 0.186 nm for sodium to 0.099 nm for chlorine.

   (a)

   What happens to the shielding experienced by the outer electrons from sodium to chlorine?

   [1 mark]

   • AIt increases greatly because there are more electrons
   • BIt decreases because the nuclear charge increases
   • CIt stays about the same because the extra electrons enter the same shell
   • DIt increases because extra shells are added

   (b)

   Which of these Period 3 atoms has the smallest atomic radius?

   [1 mark]

   • ASodium
   • BMagnesium
   • CAluminium
   • DChlorine

   (c)

   Explain why the atomic radius decreases from sodium to chlorine.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The first ionisation energies of the Period 3 elements (in kJ mol⁻¹) are: Na 496, Mg 738, Al 578, Si 786, P 1012, S 1000, Cl 1251, Ar 1521.

   (a)

   The first ionisation energy of aluminium is lower than that of magnesium. Which statement explains this?

   [1 mark]

   • AThe outer electron of aluminium is in a 3s sub-shell
   • BThe outer electron of aluminium is in a 3p sub-shell, which is higher in energy and shielded by the 3s electrons
   • CAluminium has fewer protons than magnesium
   • DAluminium has a smaller atomic radius than magnesium

   (b)

   The first ionisation energy of sulfur is lower than that of phosphorus. Which statement explains this?

   [1 mark]

   • AIn sulfur, two electrons in one 3p orbital repel each other, so one is easier to remove
   • BIn sulfur, the outer electron is removed from the 3s sub-shell
   • CSulfur has fewer protons than phosphorus
   • DSulfur has a smaller atomic radius than phosphorus

   (c)

   Explain why the first ionisation energy of argon is much higher than that of sodium.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The melting points of four Period 3 elements are: sodium 371 K, magnesium 923 K, aluminium 933 K and silicon 1687 K.

   (a)

   Explain why magnesium has a higher melting point than sodium.

   [3 marks]

   (b)

   Explain why the melting point of silicon is much higher than that of aluminium.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The melting points of four elements at the right-hand side of Period 3 are: phosphorus (P₄) 317 K, sulfur (S₈) 392 K, chlorine (Cl₂) 172 K and argon 84 K.

   (a)

   Explain the order of melting points of these four elements: sulfur > phosphorus > chlorine > argon.

   [6 marks]

   (b)

   A student says: 'Chlorine melts at a low temperature because the bond in a chlorine molecule is weak.' Evaluate this statement.

   [6 marks]

   Total for question 4: 12 marks

End of questions