Understanding The Periodic Table

FIGURE 1.38 The seven /-orbitals of a shell (with n = 3) have a very complex appearance. Their detailed form will not be used again in this text. However, their existence is important for understanding the periodic table, the presence of the lanthanoids and actinoids, and the properties of the later d-block elements. A darker color denotes a positive lobe, a lighter color a negative lobe. 

This section started with the discovery of Soddy and Fajans on radioactive decay around 1910 and the relationship of radioactive decay to the periodic table. At this point in the history, we understand the periodic table and we understand the role of isotopes in the periodic table. We have not yet understood the structure of the modern Table, i.e. first row two elements, second row eight elements, etc. That understanding can be based on Bohr theory of the hydrogen atom originally developed in 1911 and is summarized in Bohr s famous article in Zeitschrift fur Physik (Bohr 1922). 

The orbital concept and the Pauli exclusion principle allow us to understand the periodic table of the elements. An orbital is a one-electron spatial wave function. We have used orbiteils to obteiin approximate wave functions for many-electron atoms, writing the wave function as a Slater determinant of one-electron spin-orbitals. In the crudest approximation, we neglect all interelectronic repulsions and obtain hydrogenlike orbitals. The best possible orbitals are the Heu tree-Fock SCF functions. We build up the periodic table by feeding electrons into these orbitals, each of which can hold a pair of electrons with opposite spin. 

But the old quantum theory was only the beginning of quantum mechanics, which is the most powerful physical theory that has ever been devised. The transition between the old quantum theory and the new quantum mechanics is examined in this chapter, as is the impact that the updated theory had on attempts to understand the periodic table. As I argue here, the effect has been considerable, but surprisingly still incomplete, from the fundamental point of view of trying to provide a deeper explanation of the periodic system. Nevertheless, many forms of more accurate calculations can now be carried out in quantum chemistry than were even dreamt of at the time of the old quantum theory. 

C. P. Snow describes understanding the periodic table,... Quoted in Scerri, 2012, p. xviiL... 

HopefuUy, you wiU find the process of building this network of eight ideas to understand the periodic table both enUghtening and useful. The goal is to put you in a commanding position to understand, discuss, and apply the chemistry of the main-group or representative elements. 

Icons for the first five components of the interconnected network of ideas for understanding the periodic table. These components are introduced here in Chapter 9. 

The periodic law. A summary of the general vertical and horizontal periodic trends in effective nuclear charge (4,), atomic radii (r), ionization energies (IE), electron affinities (EA), and electronegativities (EN). A color version of this figure is also available inside the front cover. The existence of the color versions are indicated by icons like that shown below. The periodic law is the first component of the interconnected network of ideas for understanding the periodic table. 

The metal-nonmetal line is the fifth component of our network of interconnected ideas for understanding the periodic table. It is summarized in Figure 9.19, which shows both the diagonal stepwise line in the periodic table and the metalloid elements along that line. A color version of Figure 9.19 is shown inside the front cover of the book. In our future discussions, the metal-nonmetal line component of the network will be represented by the icon shown at left. It symbolically represents this jagged line that separates the metals from the nonmetals. 

To make sense out of the descriptive chemistry of the representative elements, we have defined and discussed the basis of the first five components of a network of interconnected ideas for understanding the periodic table. These organizing principles are (1) the periodic law, (2) the uniqueness principle, (3) the diagonal effect, (4) the inert-pair effect, and (5) the metal-nonmetal line. The definitions of these components are summarized in Table 9.5. The five components are also summarized in Figure 9.20. A color version of this figure is shown on the inside front cover of the text. 

A summary of the first five components of the network of interconnected ideas for understanding the periodic table. Each component is defined in Table 9.5. Colored versions of the figures representing the individual ideas (Figures 9.10, 9.14, 9.16, 9.18, and 9.19) and this sumrrtary figure are shown on irtside the front cover of the book. 

There are two known chlorides of lead lead(II) chloride, PbCl2, and lead(IV) chloride, PbCl4. Briefly rationalize the existence of these two compounds on the basis of the interconnected network of ideas for understanding the periodic table. Which of these would you suspect would be more saltUke— that is, which compound would have the greater ionic character Briefly rationaUze your answer in terms of another component of the network. 

THE ACID-BASE CHARACTER OF OXIDES AND HYDROXIDES IN AQUEOUS SOLUTION THE SIXTH COMPONENT OF THE INTERCONNECTED NETWORK OF IDEAS FOR UNDERSTANDING THE PERIODIC TABLE... 

In Chapter 9 we established the first five components of our interconnected network of ideas for understanding the periodic table. These included the periodic law, the uniqueness principle, the diagonal effect, the inert-pair effect, and the metal-nonmetal line. These components are summarized individually and collectively in colored figures located on the front inside cover of the book The icons for each component are shown there as well as on the bookmark pullout in the back of the text. In Chapter 10 we discussed hydrogen and the hydrides (as well as basic nuclear processes). In Chapter 11 we discussed the chemistry of oxygen, reviewed and extended our knowledge of the nature of water and aqueous solutions, and added a sixth component to our network the acid-base character of oxides and their corresponding hydroxides and oxoacids. The network with this additional component is shown in color on the top left side of the back inside cover of the book. 

Describe the eighth idea in our network of ideas for understanding the periodic table. What parts of the periodic table does it cover Give two examples (from two different groups) of applications of this new idea. Draw appropriate, well-labeled diagrams to accompany your description. 

Describe how the eighth idea in the network for understanding the periodic table applies to Group 5A. Cite two examples from this group as part of your answer. 

The first five components of the interconnected network of ideas for understanding the periodic table are developed in Chapter 9. Three additional components are added in Chapters 11,12, and 15. Figures showing the network at various stages of its development appear in the text on the following pages ... 

---