Ionisation energiesAQA A-Level Chemistry: Subtopic test

1. 1
   Compounds of Group 2 metals are used in fireworks and in building materials. The first ionisation energies of the Group 2 metals decrease from beryllium to barium. Calcium has a first ionisation energy of 590 kJ mol⁻¹ and a second ionisation energy of 1145 kJ mol⁻¹.

   (a)

   Which equation represents the second ionisation energy of calcium?

   [1 mark]

   • ACa(g) → Ca⁺(g) + e⁻
   • BCa(g) → Ca²⁺(g) + 2e⁻
   • CCa⁺(g) → Ca²⁺(g) + e⁻
   • DCa²⁺(g) → Ca³⁺(g) + e⁻

   (b)

   Which statement best explains why the first ionisation energy decreases from beryllium to barium?

   [1 mark]

   • AThe nuclear charge decreases down the group
   • BThe outer electron is further from the nucleus and more shielded, which outweighs the increase in nuclear charge
   • CThe outer electrons are held more strongly because the atoms have more protons
   • DThe outer electron is removed from a higher energy p sub-shell

   (c)

   Explain why the second ionisation energy of calcium is greater than its first ionisation energy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist is given the successive ionisation energies, in kJ mol⁻¹, of two unknown elements, X and Y, which are both in the first three periods of the periodic table. X: 496, 4563, 6913, 9544. Y: 738, 1451, 7733, 10543.

   (a)

   In which group of the periodic table is element X?

   [1 mark]

   • AGroup 2
   • BGroup 3
   • CGroup 4
   • DGroup 1

   (b)

   Which statement best explains the very large increase from the first to the second ionisation energy of X?

   [1 mark]

   • AThe second electron is removed from an inner shell, closer to the nucleus and less shielded
   • BThe nuclear charge of X increases when the first electron is removed
   • CThe second electron is removed from a different sub-shell containing paired electrons
   • DThe first electron is removed from a p sub-shell

   (c)

   Deduce the group in which element Y is found. Give a reason for your answer.

   [2 marks]

   Total for question 2: 4 marks

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

   (a)

   Explain why the first ionisation energy of aluminium is lower than that of magnesium.

   [3 marks]

   (b)

   Explain why the first ionisation energy of sulfur is slightly lower than that of phosphorus.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student is using ionisation energy data to investigate electron configurations. Data set 1 gives the first six successive ionisation energies of silicon in kJ mol⁻¹: 786, 1577, 3232, 4356, 16091 and 19805. Data set 2 gives the first ionisation energies of Group 2 in kJ mol⁻¹: Be 900, Mg 738, Ca 590, Sr 550 and Ba 503. Data set 3 gives the first ionisation energies of magnesium (738 kJ mol⁻¹) and aluminium (578 kJ mol⁻¹).

   (a)

   Explain how data set 1 provides evidence for the arrangement of electrons in shells, and deduce the electron configuration of silicon.

   [6 marks]

   (b)

   Use data sets 2 and 3 to explain the trend in the first ionisation energy down Group 2, and to explain how the change from magnesium to aluminium provides evidence for the existence of sub-shells.

   [6 marks]

   Total for question 4: 12 marks

End of questions