6 4 Ionisation energies provide information about the number of electrons and the arrangement of the electrons in an atom of an element. (a) A student’s definition of first ionisation energy is shown. First ionisation energy is the energy released when one mole of gaseous atoms loses one mole of electrons to form one mole of gaseous 1+ ions. There is one incorrect word in the student’s definition. Identify the word, giving the reason why this word is incorrect. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (b) Write an equation for the second ionisation energy of oxygen. Include state symbols. (2) Turn over 7 (c) A sodium atom has 11 protons whereas a potassium atom has 19 protons. Explain why the first ionisation energy of sodium is greater than that of potassium. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 8 (d) The successive ionisation energies for magnesium are given in the table. Electron number removed 1 2 3 4 5 6 7 8 9 10 11 12 Ionisation energy / kJ mol–1 738 1451 7733 10 541 13 629 17 995 21 704 25 657 31 644 35 463 169 996 189 371 Log (ionisation energy) 2.87 3.16 3.89 4.02 4.13 4.34 4.41 4.50 4.55 5.23 (i) Complete the table. (1) (ii) Give a reason why the logarithm of the ionisation energy, rather than just the ionisation energy, is used to plot a graph. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (iii) Give a reason why the successive ionisation energies increase. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... Turn over 9 (iv) Plot the graph of log(ionisation energy) against electron number removed. Join the individual points using straight lines. (3) (v) Identify on the graph, using a circle, the points that represent the removal of the electrons in the outermost energy level of magnesium. (1) 10 (e) Estimate a value for the first ionisation energy of oxygen given the data in the table. (1) Element First ionisation energy / kJ mol–1 carbon 1086 nitrogen 1402 oxygen ................ (Total for Question 4 = 15 marks)