A researcher records the cumulative energy required (in ) to remove successively the…
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
A researcher records the cumulative energy required (in kJmol−1) to remove successively the first eight electrons from two gaseous atoms, X and Y. The data are plotted on a graph (not shown) of cumulative ionization energy versus number of electrons removed. The following verbal description summarizes key features of the two curves:
• For both elements, the first and second electrons are removed with relatively modest energy increases (below 1500kJmol−1 each).
• For element X, a massive jump in cumulative energy occurs after the removal of the second electron; the slope of the curve increases by roughly an order of magnitude.
• For element Y, large jumps occur after removal of the third and the sixth electrons.
• After eight electrons have been removed, the cumulative ionization energy of Y is higher than that of X by approximately 25%.
Answer the following questions about elements X and Y.
(a) For each element, state the most probable number of valence electrons in the neutral atom and justify your inference from the qualitative data above.
(b) Using your answer to part (a), propose an electron configuration for the neutral atom of X and for the neutral atom of Y (noble-gas core notation is acceptable).
(c) For element Y, rationalize why two distinct large jumps—one after the third electron and another after the sixth—are observed, citing changes in subshell energy and effective nuclear charge during sequential ionizations.
(d) Both X2+ and Y3+ ions can be generated in the gas phase. Predict which ion will have the smaller ionic radius and provide a detailed explanation that references nuclear charge, shielding, and electron–electron repulsion in the cation.