In Part Four we address something especially beautiful in its inherent simplicity,¹ the understanding of the atom, the foundations of chemistry, and the makeup of everything that we see around us. Here we'll see not only how the properties of the elements are explained by quantum mechanics but also how the strange cycle of their properties is related to the electronic structure of the atoms, and how that determines their bonding to form most of what we see around us and what may be created. (For me this is the most important product of quantum mechanics: the provision of an understanding that is the practical engine of invention.)

APPROACH

Here we extend our understanding of the states of the electron in hydrogen to show what may be expected for the atoms of the rest of the elements. Our approach will be somewhat empirical and in no way presumes the full “reduction” that concerns Scerri.² However, as will be explained more fully in Chapter 14, a lot of the physics is in place, and quantum mechanics is rather compelling in providing much of our understanding of the elements and the periodic table.

I begin, in Chapters 11 and 12, by more completely defining the properties of the electron. In Chapter 13 I explain the consequences of exclusion in determining the properties of the elements and the cyclic nature of those properties as displayed in the periodic table. In Chapter 14 I examine what physically is going on in the atom to produce its chemistry and determine its size. (Strange as this may seem, the sizes of atoms are actually smaller and smaller as we consider successively heavier and heavier elements with more and more electrons within each period of the periodic table.) In Chapters 15, 16, and 17, I show how the chemical properties of the elements result in bonding to form molecules and solid materials that insulate, conduct, or semiconduct (to produce all of the modern electronics and the other devices described in Part Five).

At times I may operate conceptually beyond the level of most introductory chemistry and physics college courses, but I leave out the math normally involved and I use methods requiring no special training in math or science. Should you find the discussion at any point to be more detailed than you would like, I would suggest that you scan through indicated sections to get a sense of the physics involved, recognizing that this Part Four also provides a valuable background for understanding the fascinating inventions, the “quantum wonders,” yet to be described in Part Five.

THE PERIODIC TABLE

Everything around us is made up of the atoms or combinations of the atoms of the elements. As of October 13, 2016, 118 different types of atoms have been discovered or created.³ These are the building blocks, respectively, of the 118 different elements, each with its own distinct set of properties. As we consider each successively heavier element, one after the other, the properties of these atoms, these elements, seem to cycle periodically, nearly repeating themselves. I summarize this behavior by listing the elements in what is called a periodic table. A brief, interesting history of the development of such tables, and a bit of the life of the charismatic character mainly responsible for that development is presented in Appendix B. I would recommend that you take a break from the theory at this point, and just read through Appendix B for the entertainment and background that it provides.

Many different forms of periodic tables have been produced: some listing the elements by atomic number in columns, some in spirals, some in rows. What is common to all of them is that each period in which the properties of the elements seem to repeat themselves is marked by the presence of one of the “inert” elements that were originally thought to react and combine with no other elements, that is, one of the noble gasses. And the numbers of elements between each pair of noble gasses is always the same, regardless of the form of the table.

In Table B.2, for example, counting through the elements by atomic number successively, starting with hydrogen, atomic number 1, at the bottom left, we immediately have the inert noble gas helium, atomic number 2, at the bottom right. We move 2 elements to helium. Through the next row we have 8 more elements to the noble gas neon. Through the next row, we have 8 more to argon, then 18 more to krypton, 18 more to xenon, and 32 more to radon. This “2, 8, 8, 18, 18, 32” sequence will be the same in all periodic tables.

THE ELECTRONIC STRUCTURE OF THE ATOM

Scerri provides an excellent history of how the electron structure of the atom was determined in his Chapter 7, “The Electron and Chemical Periodicity” and in his Chapter 8, “Electronic Explanations of the Periodic System Developed by Chemists.”⁴ I summarize this history very briefly now as part of this introduction.

With the discovery of the electron in 1897 and the subsequent realization that the chemical properties of the elements are related to the number of electrons in their atoms, physicists and chemists sought to understand the periodic table in terms of the population of electron states by electrons in the atoms of each of the elements. The chemists were inductive and empirical, and they focused mainly on the manner in which the elements interacted with other elements. They were fairly successful in evolving an empirical set of rules that described the arrangement of the table.

The physicists, meanwhile, sought to overcome some of the contradictions of classical theory and began in 1900 to evolve a quantum theory (as we've described) that might allow the periodicity of the table to be deduced from the physics of the atom. As presented earlier, the lead proponent in this activity was the Danish physicist and later Nobel Prize winner Niels Bohr. But, as Scerri points out, Bohr's approach was not so much predictive as empirical in guiding the form of the physics based on what he already knew about the elements and the table.

The physicists succeeded in solving exactly for the possible spatial states for the electron in the hydrogen atom, as described in the chapters of Part Two of this book. While that success has been difficult to extend mathematically to many-electron atoms except by approximation, the hydrogen results nevertheless provide a guide for qualitatively predicting the electronic structure of these more complex atoms and for understanding the arrangement of the periodic table. As you will see, it all depends on energy.