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THE PERIODIC TABLE
Past, Present, and Future
Copyright © 2020 by World Scientific Publishing Co. Pte. Ltd.
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About the Author
Geoff Rayner-Canham, FCIC, FRSC, has published widely on aspects of chemistry education, particularly inorganic chemistry. With Tina Overton, he is coauthor of Descriptive Inorganic Chemistry, which is currently in its 6th edition and which has been translated into six other languages. Geoff’s main research focus has been on the history of women in science — particularly chemistry. This research has been undertaken jointly with his partner, Marelene Rayner-Canham. In addition to many research papers, they have coauthored six books, the latest being Pioneering British Women Chemists: Their Lives and Contributions.
For 20 years, accompanied by some of his students, Geoff has taken chemistry outreach to remote and isolated schools in rural Newfoundland, Labrador, Nunavut, and coastal Quebec. He has also been coauthoring a series of articles with his Inuk student, Chaim Andersen, on Chemistry and Inuit Life & Culture.
With his colleague, Debbie Wheeler, Geoff codeveloped, and has been coteaching, the first online distance chemistry courses offered by Memorial University. One of the courses received a Canadian award for innovation in distance course technology. Students from as far away as Wuhan, China, and Sydney, Australia, have taken these courses. For his outreach and for excellence in chemistry teaching, Geoff has received the Chemical Institute of Canada, Chemical Education Award; the National Science and Engineering Research Council of Canada PromoScience Award; and a 3M Teaching Fellowship.
Geoff continues to teach and undertake research at the Grenfell Campus, Memorial University, Corner Brook, Newfoundland & Labrador, Canada, where he currently holds the rank of Honorary Research Professor.
Contents
About the Author
Introduction
Chapter 0The Periodic Table Exploration Begins!
Reference
Chapter 1Isotopes and Nuclear Patterns
Proton–Neutron Ratio
The Cobalt–Nickel and Tellurium–Iodine Atomic Mass Anomalies
Nuclear Shell Model of the Nucleus
Limits of Stability
Commentary
References
Chapter 2Selected Trends in Atomic Properties
Electronegativity
Electron Gain and Loss
Ionization Energy
Electron Affinity
Relativistic Effects on Atomic Properties
Commentary
References
Chapter 3First Period Problems
Hydrogen Location: An Overview
… And Then There Is Helium
Commentary
References
Chapter 4The Group 3 Problem
A History of the Debate
Commentary
References
Chapter 5Categorizations of the Elements
Nonmetals, Metals, and “In-Betweens”
Main Group Appellations
d-Block Metal Appellations
Other Appellations
Commentary
References
Chapter 6Isoelectronicity
Historical Definitions of Isoelectronic
Modern Definitions of Isoelectronic
Isoelectronicity: The Future
Commentary
References
Chapter 7Group and Period Patterns among the Main Group Elements
Main Group Elements
Group Trends
Group 1 (Alkali Metals)
Group 2 (Alkaline Earth Metals)
Group 13 (Triels)
Group 14 (Tetrels)
Group 15 (Pnictogens)
Group 16 (Chalcogens)
Group 17 (Halogens)
Group 18 (Aerogens)
Periodic Trends
Commentary
References
Chapter 8Patterns among the Transition Metals
What Is a Transition Metal?
Previous Classifications of Transition Metals
Categorizations of the Transition Metals
Categorizing the Early 4d–5d Elements
The Platinum Metals
Is There, in Fact, a Group 11?
A Hybrid Solution
Commentary
References
Chapter 9Group (n) and Group (n + 10) Relationships
Going Back to the Past
Definition of the Group (n) and Group (n + 10) Relationship
Group 3 and Group 13
Group 4 and Group 14
Group 5 and Group 15
Group 6 and Group 16
Group 7 and Group 17
Group 8 and Group 18
Group 1 and Group 11
Group 2 and Group 12
A Curious (n + 5) and (n + 10) Case
Commentary
References
Chapter 10Chemical “Knight’s Move” Relationship
The Group (n)/Period (m) and Group (n + 2)/Period (m + 1) Linkages
Laing’s Knight’s Move (K-M) Claims
Reevaluation of the Knight’s Move Relationship
Knight’s Move Relationships among “Double Pairs”
The Knight’s Move Relationship and the “Inert Pair” Effect
Commentary
References
Chapter 11Isodiagonality
Isodiagonality
Explanations for Isodiagonality
Isodiagonality of Lithium and Magnesium
Isodiagonality of Beryllium and Aluminum
Isodiagonality of Boron and Silicon
Isodiagonality of Carbon and Phosphorus
Isodiagonality of Nitrogen and Sulfur
Isodiagonality of Vanadium and Molybdenum
Isodiagonality of Tellurium and Astatine
Evidence-Based Isodiagonality
Commentary
References
Chapter 12Lanthanoids, Group 3, and Their Connections
Yttrium and Scandium
The 4f Elements
The Lanthanoids
Ion Charges of the Lanthanoids
Restructuring the Lanthanoids
External Lanthanoid Relationships
Commentary
References
Chapter 13Actinoid and Post-
Actinoid Elements
The Actinoid Elements
Oxidation States of the Actinoids
Post-Actinoid Elements
And Beyond …
Commentary
References
Chapter 14Pseudo-Elements
Pseudo-Elements
Pseudo-Halogens
Combo Elements
Superatoms
Synthetic Metals
Commentary
References
Index
Introduction
“Periodic Properties? That’s easy! Properties down a couple of Groups, properties across a sample Period, done!” A not uncommon view. Yet there is a richness of relationships, some obvious, some not, which makes an in-depth look at the chemical elements a rewarding adventure. Ronald Rich eloquently described the lure of periodicity in all its manifestations:
One of the fascinations of inorganic chemistry is the existence of a wide variety of relationships among the elements and their properties-relationships that show an encouraging degree of order, but a tantalizing variability and novelty. These qualities make the “family of elements” an apt metaphor: while members of a family have much in common, each member also has his[/her] own individual personality.
There have been some 20th century monographs on chemical periodicity. However, to be honest, the old Periodic Table monographs are boring … no, very boring … no extremely boring. As are the chapters on the Periodic Table in most textbooks. A litany of dry facts usually emphasizing that everything can be explained in terms of Groups and Periods; that everything is known; that there is only one definitive Periodic Table; and that apart from the genius of Mendeléev, rarely is any other human involvement described.
How incredibly far from the truth in all these factors!
•The Periodic Table is fascinating — as I hope, you, the Reader, will discover.
•Groups and Periods are only one small facet of linkages among the chemical elements.
•There are still avenues of exploration and with many discoveries, new possibilities arise.
•There is no one-fits-all-uses Periodic Table — there are different arrangements to better explain some aspect of element linkages.
•The Periodic Table is a human construct, as can be seen from the names mentioned herein. And in recent times, seven individuals, in particular, have contributed greatly to modern philosophies of the Periodic Table and of the elements therein: Stephen Hawkes, William Jensen, Michael Laing, Pekka Pyykkö, Guillermo Restrepo, R. T. Sanderson, and Eric Scerri. The Reader will see their names (and many others) sprinkled in the text and among the Chapter References.
This book is not a data-filled comprehensive (and boring) compilation. Instead, by looking at some patterns and trends from different perspectives, the Author hopes that the Reader will find this book stimulating and thought-provoking. Without doubt, there are additional interesting and/or curious linkages and patterns of which the Author is unaware. Any Reader spotting an overlooked similarity or pattern is asked to bring it to the attention of the Author at: [email protected].
In closing, my Grenfell colleague Chris Frazee, and my partner, Marelene Rayner-Canham, are thanked for reading the entire manuscript (Marelene, many times) in an endeavor to minimize the errors therein.
Geoff Rayner-Canham
Chapter 0
The Periodic Table Exploration Begins!
“The time has come,” the Walrus said,
To talk of many things:
Of shoes—and ships—and sealing wax—
Of cabbages—and kings—
And why the sea is boiling hot—
And whether pigs have wings.”
Thus spake the Walrus to the Carpenter (Figure 0.1) in Alice Through the Looking Glass [1].
Here, in this treatise, Gentle Reader, you will be led through the world of the Periodic Table; a world even more exciting, more wondrous, more bizarre, than anything Lewis Carroll could have ever imagined.
Figure 0.1 The Walrus, the Carpenter, and the Little Oysters.
Reference
1.L. Carroll, More Annotated Alice: Alice’s Adventures in Wonderland and Through the Looking Glass and What Alice Found There, with notes by Martin Gardner; Random House, New York, NY, 220 (1990).
Chapter 1
Isotopes and Nuclear Patterns
In the early decades of modern chemistry, atomic mass (weight) of an element was a major topic for debate and heated dispute. The original Periodic Tables were constructed in terms of order of atomic mass. Any irregularities in order were excused away. With the discovery of atomic number and its use as the foundation of the modern Periodic Table, inorganic chemists seem to have largely ignored patterns in element isotopes. Not only do such patterns explain average atomic mass irregularities, but they reveal some fascinating nuclear chemistry. In addition, the shell model of the nucleus is important in the synthesis of new chemical elements.
In this chapter, the principles of nuclear physics will only be developed to a depth that will aid the understanding of the properties of atoms. For example, the origins of the nuclear strong force, which holds nuclear particles together, is best explained in terms of constituent quarks [1], far beyond the realm of this book. Similarly, the nuclear shell model will be used and applied without delving deeply into its quantum mechanical basis.
Proton–Neutron Ratio
For the lower proton numbers, P, the number of neutrons, N, is approximately matching. With increasing numbers of protons, the numbers of neutrons necessary for nuclear stability increase at a faster rate. For example, the oxygen-16 nucleus has a P:N ratio of 1:1.0, while that of uranium-238 has a P:N ratio of 1:1.6. Figure 1.1 shows a plot of P versus N for stable isotopes [2]. The figure uses the conventional symbol, Z, for the number of protons (from the German, Zahl, for “number” [3]). This need for ever-increasing proportions of neutrons to “stabilize” the nucleus has major implications for superheavy element synthesis as will be shown later in this chapter.
Figure 1.1 Plot of neutrons to protons in stable nuclei (adapted from Ref. [2]).
Nuclear Spin Pairing
Different from electron behavior, spin pairing is an important factor for nucleons. In fact, of the 273 stable nuclei, 54% have even numbers of both protons and neutrons (Table 1.1). There is similarly a predominance of even–even nuclei for long-lived radioactive isotopes; those that date back to the origins of the elements [4]. Only four stable nuclei have odd numbers of both protons and neutrons. These stable odd–odd nuclei are hydrogen-2, lithium-6, boron-10, and nitrogen-14 [1]. The only four long-lived odd–odd radioactive isotopes are potassium-40, vanadium-50, lanthanum-138, and lutetium-176.
Table 1.1 Distribution of isotopes
Spin pairing increases the binding energy; thus, an odd–odd combination has a weaker binding energy than other nuclei, especially even–even. If we look at a series of atoms with the same nucleon (mass) number but differing numbers of protons and neutrons, known as isobars, an interesting pattern emerges, known as the Mattauch Isobar Rule:
The Mattauch Isobar Rule states that: if two adjacent elements in the Periodic Table have isotopes of the same nucleon number, then at least one of the isobars must be a radionuclide (i.e., radioactive).
This phenomenon is illustrated by the “triplet” isobars, argon-40, potassium-40, and calcium-40, where the argon and calcium isotopes are both stable, while the intervening isobar of potassium is radioactive.
The lack of any stable isotopes of technetium and promethium have always been a notable feature of the Periodic Table. Johnstone et al. have used the Mattauch Isobar Rule as a justification of the instability of all technetium isotopes [2]. The neighbors on either side, molybdenum and ruthenium, have six and seven stable isotopes, respectively. These isotopes span the range of “normal” P:N ratios, thus precluding any technetium isotope having a possibility of existence within that range.
The underlying phenomenon was discussed by Suess. He
accounted for the instabilities for both technetium and promethium as follows [5]:
After the filling of the 50- and 82-neutron shell [see discussion below], an upward shift in the β decay energies occurs equivalent to the drop in the binding energy of the last neutron. This shift is somewhat larger, however, for the odd Z than for the odd N nuclei, indicating that the drop is not equal for paired and for unpaired neutrons.... Thus, for a given I [mass number], the isobars with odd numbers of neutrons become stable at a lower mass number than those with an odd number of protons. This difference is large enough to cause the β-instability of all nuclei with a certain odd number of protons, incidentally those of Z = 43 and 61.
Even Numbers of Nucleons
Elements with even numbers of protons tend to have large numbers of stable isotopes, whereas those with odd numbers of protons tend to have one or, at most, two stable isotopes. For example, cesium (55 protons) has just one stable isotope, whereas barium (56 protons) has seven stable isotopes. The greater stability of even numbers of protons in nuclei can be related to the abundance of elements on Earth. As well as the decrease of abundance with increasing atomic number, we see that elements with odd numbers of protons often have an abundance about one-tenth that of their even-numbered neighbors (see Figure 1.2). This observation is known as the Oddo–Harkins Rule [6]:
The Oddo–Harkins Rule states that an element with an even atomic number is more abundant than either adjacent nucleus with an odd number of protons.
At the end of the curve, there is a “drop-off.” With only radioactive isotopes, the abundances of thorium and uranium have diminished with time. The reduction in abundance over time is also true for other radioactive isotopes, especially potassium-40 [7].
There are two notable exceptions to the Oddo–Harkins Rule. Beryllium would be expected to be much more abundant than it is, while nitrogen would be expected to be significantly less [8]. One might expect beryllium-8 with its 1:1 P:N ratio to be common. However, this nucleus has an extremely short lifetime, splitting into two helium-4 nuclei (helium-4 is “double magic” as we will discuss in the following).
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