A plotted data set shows first-ionization energy versus atomic number for elements 19…
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
A plotted data set shows first-ionization energy versus atomic number for elements 19 through 38. From K (19) to Zn (30) the values rise modestly and form a broad plateau; from Ga (31) through Kr (36) the curve rises more steeply, culminating in a pronounced peak at Kr. A slight dip is noted at atomic number 37 (Rb), followed by an increase to Sr (38).
Use this description to analyze periodic behavior in the fourth period.
(a) Delineate which contiguous atomic-number interval on the graph corresponds to transition-metal elements and which corresponds to main-group elements.
(b) Explain why the increase in first-ionization energy is relatively subdued across the transition-metal portion of the graph compared with the main-group portion.
(c) Based on the slope immediately preceding and following Zn (atomic number 30), predict whether Zr (atomic number 40) is expected to have a first-ionization energy closer to that of Y (39) or Nb (41). Support your prediction with reference to the trend observed in the fourth period.
(d) Using shielding and effective nuclear charge arguments, compare the expected magnitude of Zeff experienced by the outermost electron of Zn with that experienced by Ga, and relate this comparison to their positions on the graph.