CHEMISTRY · Single correct · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
Three main-group elements X, Y, and Z are successive members of the third period (left to right). Some of their atomic properties are shown.
Property X Y Z
First ionization energy (kJ/mol) 496 738 1000
Electron affinity (kJ/mol) –48 –78 –190
Atomic radius (pm) 186 160 125
A student proposes the following statements to explain the variation in these properties.
I. The effective nuclear charge experienced by valence electrons increases from X to Z.
II. The simultaneous increase in first ionization energy and the magnitude of electron affinity from X to Z is primarily a consequence of statement I.
III. The decrease in atomic radius from X to Z contradicts statement I because a stronger nucleus should expand, not contract, the electron cloud.
Which of the following is the most accurate evaluation of the student’s statements?
(a) Only I is correct.
(b) I and II are correct; III is incorrect.
(c) I and III are correct; II is incorrect because EA should decrease.
(d) II and III are correct; I is incorrect.