The Periodic Table Summarized

The Periodic Table consists of 18 groups, corresponding to the filling of 

The importance of interelectronic repulsion in the understanding of polyatomic systems was discussed, followed by discussions of orbital penetration and screening effects that decide the breakdown in degeneracy of the hydrogen-like orbitals. 

The spin quantum number was introduced, leading to a discussion of the Pauli exclusion principle and the anti-symmetric properties of real wave functions. 

The fundamental theoretical principles were used to describe the electronic configurations of the elements and the construct the general form of the modern Periodic Table. 

Hund s rules were stated and rationalized, and the aujhau building-up principle was used to describe electronic configurations of the elements. Exceptions to regular fillings of sets of orbitals were discussed. 

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The development of the structural theory of the atom was the result of advances made by physics. In the 1920s, the physical chemist Langmuir (Nobel Prize in chemistry 1932) wrote, The problem of the structure of atoms has been attacked mainly by physicists who have given little consideration to the chemical properties which must be explained by a theory of atomic structure. The vast store of knowledge of chemical properties and relationship, such as summarized by the Periodic Table, should serve as a better foundation for a theory of atomic structure than the relativity meager experimental data along purely physical lines. ... 

The concept of chemical periodicity is central to the study of inorganic chemistry. No other generalization rivals the periodic table of the elements in its ability to systematize and rationalize known chemical facts or to predict new ones and suggest fruitful areas for further study. Chemical periodicity and the periodic table now find their natural interpretation in the detailed electronic structure of the atom indeed, they played a major role at the turn of the century in elucidating the mysterious phenomena of radioactivity and the quantum effects which led ultimately to Bohr s theory of the hydrogen atom. Because of this central position it is perhaps not surprising that innumerable articles and books have been written on the subject since the seminal papers by Mendeleev in 1869, and some 700 forms of the periodic table (classified into 146 different types or subtypes) have been proposed. A brief historical survey of these developments is summarized in the Panel opposite. 

We see that the rows of the periodic table arise from filling orbitals of approximately the same energy. When all orbitals of similar energy are full (two electrons per orbital), the next electron must be placed in an s orbital that has a higher principal quantum number, and a new period of the table starts. We can summarize the relation between the number of elements in each row of the periodic table and the available orbitals of approximately equal energy in Table 15-V. 

What I hope to have added to the discussion has been a philosophical reflection on the nature of the concept of element and in particular an emphasis on elements in the sense of basic substances rather than just simple substances. The view of elements as basic substances, is one with a long history. The term is due to Fritz Paneth, the prominent twentieth century radio-chemist. This sense of the term element refers to the underlying reality that supports element-hood or is prior to the more familiar sense of an element as a simple substance. Elements as basic substances are said to have no properties as such although they act as the bearers of properties. I suppose one can think of it as a substratum for the elements. Moreover, as Paneth and before him Mendeleev among others stressed, it is elements as basic substances rather than as simple substances that are summarized by the periodic table of the elements. This notion can easily be appreciated when it is realized that carbon, for example, occurs in three main allotropes of diamond, graphite and buckminsterfullenes. But the element carbon, which takes its place in the periodic system, is none of these three simple substances but the more abstract concept of carbon as a basic substance. 

The pattern of ion formation by main-group dements can be summarized by a single rule for atoms toward the left or right of the periodic table, atoms lose or gain electrons until they have the same number of electrons as the nearest noble-gas atom. Thus, magnesium loses two electrons and becomes Mg2+, which has the same number of electrons as an atom of neon. Selenium gains two electrons and becomes Se2+, which has the same number of electrons as krypton. 

Rhenium has good chemical resi stance due to its position in the periodic table nextto the noble metal s of the platinum group. However, it oxidizes readily. Its properties are summarized in Table 6.10. 

Our picture of atomic architecture is now compiete. Three kinds of particles—electrons, protons, and neutrons-combine in various numbers to make the different atoms of aii the eiements of the periodic table. Table 2-1 summarizes the characteristics of these three atomic buiiding biocks. 

The periodicity of chemical properties, which Is summarized In the periodic table. Is one of the most useful organizing principles in chemistry. Periodic patterns also provide information about electron arrangements in atoms. 

Two fundamental features of orbitals form the basis of periodicity and are summarized on the periodic table in Figure 8-14. 

A soft Lewis base has a large donor atom of high polarizability and low electronegativity. Iodide ion has its valence electrons in large a = 5 orbitals, making this anion highly polarizable and a very soft base. Other molecules and polyatomic anions with donor atoms from rows 3 to 6 are also soft bases. To summarize, the donor atom becomes softer from top to bottom of a column of the periodic table. 

Drawing a Conclusion Summarize what you have learned about the organization of the periodic table. How accurate were your hypotheses ... 

Many observations concerning these trends had been made over the years, and in the 1950s S. Ahrland, J. J. Chatt, and M. Davies presented a classification of metals based on their preferred interaction with donor atoms. Class A metals are those that interact preferentially when the donor atom is in the first row of the periodic table. For example, they prefer to bond to N rather than P donor atoms. Class B metals are those which interact better when the donor atom is in the second row of the periodic table. For example, a class B metal would bond better to P than to N. The following table summarizes the behavior of metal atoms according to this classification. 

Another chapter (Chapter 4) is entitled Intermetallic reactivity trends in the Periodic Table . The Periodic Table, indeed (or Periodic Law or Periodic System of Chemical Elements), is acknowledged to play an indispensable role in several different sciences. Especially in inorganic chemistry it represents a fundamental classifi-catory scheme and a means of systematizing data with a clear predictive power. Inorganic chemists have traditionally made considerable use of the Periodic Table to understand the chemistry of the different elements. With a few exceptions (as detailed in the same chapter), metallurgists and intermetallic chemists have made little use of this Table to understand and describe the properties of metals and alloys we believe, however, that it may be a useful tool also in the systematics of descriptive intermetallic chemistry (as exemplified in the subsequent chapter (Chapter 5)). In several paragraphs of Chapter 4, therefore, different aspects of the Periodic Table and of its characteristic trends are summarized. 

On the basis of the Periodic Table, topics of intermetallic systematics will be presented in the next chapter. In the present chapter the Periodic Table will be revisited and its structure and subdivisions summarized. In relation also to some concepts previously presented, such as electronegativity, Mendeleev number, etc. described in Chapter 2, typical property trends along the Table will be shown. Strictly related concepts, such as Periodic Table group number, average group number and valence-electron number will be considered and used in the description and classification of intermetallic phase families. 

Only a few relevant points about the atomic structures are summarized in the following. Table 4.1 collects basic data about the fundamental physical constants of the atomic constituents. Neutrons (Jn) and protons (ip), tightly bound in the nucleus, have nearly equal masses. The number of protons, that is the atomic number (Z), defines the electric charge of the nucleus. The number of neutrons (N), together with that of protons (A = N + Z) represents the atomic mass number of the species (of the nuclide). An element consists of all the atoms having the same value of Z, that is, the same position in the Periodic Table (Moseley 1913). The different isotopes of an element have the same value of Z but differ in the number of neutrons in their nuclei and therefore in their atomic masses. In a neutral atom the electronic envelope contains Z electrons. The charge of an electron (e ) is equal in size but of opposite sign to that of a proton (the mass ratio, mfmp) is about 1/1836.1527). 

Comments on some trends and on the Divides in the Periodic Table. It is clear that, on the basis also of the atomic structure of the different elements, the subdivision of the Periodic Table in blocks and the consideration of its groups and periods are fundamental reference tools in the description and classification of the properties and behaviour of the elements and in the definition of typical trends in such characteristics. Well-known chemical examples are the valence-electron numbers, the oxidation states, the general reactivity, etc. As far as the intermetallic reactivity is concerned, these aspects will be examined in detail in the various paragraphs of Chapter 5 where, for the different groups of metals, the alloying behaviour, its trend and periodicity will be discussed. A few more particular trends and classification criteria, which are especially relevant in specific positions of the Periodic Table, will be summarized here. 

Divides in the Periodic Table. A particular scheme of subdivision of the Periodic Table has been presented by Stone (1979) and applied to the classification of alloying tendencies it is summarized in Fig. 4.7. In this figure, a number of vertical lines, termed divides , have been drawn in particular positions of the Table. These are so placed that any element near a divide, and on one side of it, will form a compound or compounds with a counterpart element at the other side of that divide or, in other words, will form compounds with a specific bonding mechanism. 

Intermetallic chemistry of Be, Mg, Zn, Cd and Hg 5.12.4.1 Phase diagrams of the Be, Mg, Zn, Cd and Hg alloys. The systematics of the compound formation of these metals in their binary alloys with the different elements is summarized in Fig. 5.33. On the overall they give a rather complex picture even so a number of relationships and similarities between various pairs of metals may be singled out. To go into this point in more detail, in the same figure a comparison has also been made with the compound formation patterns of Ca and A1 which are described in 5.4 and 5.13 but are close in the Periodic Table to the metals here considered. The similarity between the Be and Zn patterns may be underlined, as also that between Be and Al, being an example of the so-called diagonal relationships presented in 4.2.2.2. 

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). 

In this chapter, the details of several types of Ir-complex-catalyzed cycloadditions have been summarized. Although, compared to other late transihon-metal com-plexes-such as those of Pd, Ni, Ru and Rh-the examples are few in number, some notable Ir-catalyzed cyclizations have recently been reported which cannot be achieved when uhlizing other metal catalysts. Until now it has not yet been possible to identify any dishnct explanation for the unique reachvity of iridium, and in parhcular its different reachvity compared to rhodium, which is located just above iridium in the Periodic Table of the elements. Nonetheless, many further developments of efficient and prachcal Ir-catalyzed cycloadditions are to be expected in the near future. 

The last chapter, which I have called an epilogue, is also somewhat different from the others. It is a condensed history of twentieth-century particle physics. The search for an understanding of the constituents of matter did not end with Bohr s explanation of the properties of the periodic table after all. On the contrary, the quest continued by being passed from the hands of the chemists into those of the physicists. Because I chose to discuss this material within the framework of a single chapter, I was forced to omit some of the details. However, I think it sufficiently summarizes the paths that the physicists followed once they took on the task of trying to determine what the universe was made of. 

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