The Periodic Table. Geoff Rayner-Canham
in which relativistic effects are discussed are the color of gold [56, 57] and the liquid phase of mercury at room temperature [58]. In this section, the focus will be on the relativistic explanation for the formation of auride and platinide ions and then in later chapters on some other relevant relativistic phenomena.
Though the electrons in all atoms experience some degree of relativistic effects, they only become important for the heavier elements. There are two significant factors that can be ascribed to relativistic effects [59] (Figure 2.9 shows both factors for the 5d, 6s, and 6p energy levels):
Figure 2.9 Nonrelativistic and relativistic energy levels for the 5d, 6s, and 6p orbitals (adapted from Ref. [59]).
•Changing in relative energy levels of atomic orbitals
s orbitals decrease substantially in energy and p orbitals decrease to a lesser extent when relativistic effects are taken into consideration. This results in increased shielding of the nucleus, causing d orbitals and f orbitals to increase in energy.
•Splitting of energy levels having l > 0 into two sublevels as a result of spin–orbit coupling
p levels split into p1/2 and p3/2 while the d levels split into d3/2 and d5/2 levels.
Platinum and Gold Electron Affinities
It is relativistic effects that can explain the high EA1 for platinum and gold. The additional electron enters the 6s orbital:
Figure 2.10 Plot of ratio of relativistic to nonrelativistic atom radii for the 6s orbital (adapted from Ref. [60]).
As can be seen from Figure 2.10, the relativistic decrease in relative radius for an added 6s electron reaches a minimum at gold, with the value for platinum being not substantially different [60]. That is, there will be a greater effective nuclear charge on any additional 6s electron for platinum and gold than would be expected without taking relativistic effects into account.
Commentary
In this chapter, a mere selection of atomic periodic properties have been chosen for discussion. In this way, the Reader is not overwhelmed by endless tables and graphs of data. Those who wish to indulge should look elsewhere. This book is designed to make the many concepts of elemental relationships become alive and stimulating, not boring and soporific. The chapter has ended with an introduction to relativistic effects. This oft-overlooked aspect will not be simply a passing reference, but a topic that will be revisited in different contexts in later chapters.
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