Ionisation energiesEdexcel A-Level Chemistry: Subtopic test

1. 1
   Element X is in Period 3 of the periodic table. Its first five successive ionisation energies, in kJ mol⁻¹, are: 1st 738, 2nd 1451, 3rd 7733, 4th 10543, 5th 13630.

   (a)

   In which group of the periodic table is element X?

   [1 mark]

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

   (b)

   Which equation represents the third ionisation energy of X?

   [1 mark]

   • AX(g) → X³⁺(g) + 3e⁻
   • BX²⁺(g) → X³⁺(g) + e⁻
   • CX²⁺(s) → X³⁺(s) + e⁻
   • DX³⁺(g) + e⁻ → X²⁺(g)

   (c)

   Explain why the third ionisation energy of X is much greater than its second ionisation energy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The first ionisation energies of the Group 1 metals lithium, sodium, potassium and rubidium are 520, 496, 419 and 403 kJ mol⁻¹ respectively.

   (a)

   Which statement best explains why the first ionisation energy decreases down Group 1?

   [1 mark]

   • AThe nuclear charge decreases down the group
   • BThe atoms contain fewer electrons
   • CThe outer electron is further from the nucleus and more shielded, so it is held less strongly
   • DThere is less shielding by inner electrons

   (b)

   Which is the most likely first ionisation energy of caesium, the next element in Group 1?

   [1 mark]

   • AAbout 376 kJ mol⁻¹
   • BAbout 410 kJ mol⁻¹
   • CAbout 450 kJ mol⁻¹
   • DAbout 520 kJ mol⁻¹

   (c)

   Explain why the first ionisation energy of rubidium is lower than that of sodium.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   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 and Ar 1521.

   (a)

   Explain the general increase in first ionisation energy from sodium to argon.

   [3 marks]

   (b)

   Explain why the first ionisation energy of aluminium is lower than that of magnesium, although aluminium has a greater nuclear charge.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The successive ionisation energies of aluminium, in kJ mol⁻¹, are: 1st 578, 2nd 1817, 3rd 2745, 4th 11577, 5th 14842 and 6th 18379. The first ionisation energies of some other elements, in kJ mol⁻¹, are: helium 2372, neon 2081, argon 1521 and sodium 496.

   (a)

   Explain why the successive ionisation energies of aluminium increase, and how the data show that aluminium is in Group 3.

   [6 marks]

   (b)

   Explain the decrease in first ionisation energy from helium to neon to argon, and explain why the first ionisation energy of sodium is much lower than that of neon.

   [6 marks]

   Total for question 4: 12 marks

End of questions