Representative elements properties

The integration is over all the space and spin coordinates of electrons 2, 3,..., m. Many of the operators that represent physical properties do not depend on spin, and so we often average-out over the spin variable when dealing with such properties. The chance of finding electron 1 in the differential space element dt] with either spin, and the remaining electrons anywhere and with either spin is... 

Although the physical properties of the d-block elements are similar, the chemical properties of these elements are so diverse that it is impossible to summarize them fully. We can, however, observe some of the major trends in properties within the d block by considering the properties of certain representative elements, particularly those in the first row of the block. 

Therefore the number of half-filled orbitals indicates the number of bonds that the atoms can form. Elements in the same group of the periodic table exhibit similar chemical properties as they have the same number of valence electrons. We will explain bond formation of one representative element from each main group. The other elements found in the same group generally form bonds in a similar way. 

By using a systematic procedure to find the relevant element properties representing the alloying behaviour of binary systems, Villars (1983, 1985) defined three expressions for atomic properties which enable systems that form compounds to be separated from those that do not. 

What do elements look like How do they behave Can periodic trends in the properties of elements be observed You cannot examine all of the elements on the periodic table because of limited availability, cost, and safety concerns. However, you can observe several of the representative elements, classify them, and compare their properties. The observation of the properties of elements is called descriptive chemistry. 

Elements that appear in the s block and the p block are called either the main group elements or the representative elements. Chemists give them these names because, collectively, these elements are representative of a wide range of physical and chemical properties. Among the main group elements, for example, you will find metals, non-metals, metalloids. 

Mendeleev observed that there were some gaps in his table, empty spaces to which no element was assigned. He concluded that these represented elements that had not yet been discovered. For example, there was a gap under boron, so Mendeleev concluded that it must be an unknown element with properties like boron. He named it eka-boron ( eka is Sanskrit for the numeral one). Similarly, there were gaps under aluminum and silicon. Mendeleev called these missing elements eka-aluminum and eka-silicon. The positions of the missing elements in his table allowed him to estimate their atomic weights and also to describe their chemical and physical properties accurately. 

The 112 known elements—there may be more by the time you read this—combine to form millions of compounds. That is far more than we could study individually. Moreover just learning a string of isolated facts would not build the insight we need to devise new compounds. It is far more useful to study a select group of representative elements and their compounds. In this and the next two chapters, we use the periodic table as our guide in this highly selective journey. The topics of these chapters are commonly called descriptive chemistry—the description of the preparation, properties, and applications of elements and their compounds. 

The fact that the co-ordination number for so many elements is six, and is generally independent of the nature of the co-ordinated groups, has made A. Werner suggest that the number is decided by available space rather than affinity, and that six is usually the maximum number which can be fitted about the central atom to form a stable system. Consequently, the co-ordination number represents a property of the atom which enables the constitution of molecular compounds to be referred back to actual linkings between definite atoms. A molecular compound is primarily formed through the agency of secondary valencies and, just as primary valencies determine the number of univalent atoms or their equivalent which can be linked to a central atom, so secondary valencies determine the number of mols. which can be attached to the central atom. The secondary valency is often active only towards definite mol. complexes, and hence the formation of additive compounds with other mol. complexes does not occur. Accordingly, the number of secondary valencies which are active towards different molecules is not always the same. 

Optimized Geometries. As the elements of the NMR shielding tensor for a nucleus represent local properties, the most important geometrical parameter influencing the value of the 19F shielding constant can be expected to be the length of the bond which attaches the fluorine to the benzene ring. The optimized values of the carbon-fluorine... 

The major element content and mineralogy of air-borne particles reflect closely those of continental soils and shales, although atmospheric particulates also include materials of oceanic origin (Delaney et al., 1967), and show considerable enrichments in some trace metals (Buat-Menard and Chesselet, 1979). The average composition of shales and soils (Table 9.8) was chosen to represent the properties of dust transported from the continents to the ocean. Fluxes of elements in atmospheric transport to the ocean are given in Table 9.14. 

Because the noble gases represent elements that are of limited chemical reactivity, there is a progression in physical properties that reflects the increasing atomic weight of the gases. Several of the more important and relevant properties of the gases are shown in Table 17.1. 

We have seen that the periodic table originated as a way to portray the systematic properties of the elements. Mendeleev was primarily responsible for first showing its usefulness in correlating and predicting the elemental properties. In this section we will summarize much of the information available from the table. We will also illustrate the usefulness of the table by discussing the properties of a representative group, the alkali metals. 

The essence of the periodic table is that members of each group of representative elements exhibit similar chemical properties that change in a regular way. The quantum mechanical model has allowed us to understand that the similarity of properties of the atoms in a group arises from the identical valence electron configurations shared by group members. It is the number and type of valence electrons that primarily determine an atom s chemistry. 

The periodic table. The elements in the A groups are the representative elements. The elements shown in pink are called transition metals. The dark line approximately separates the nonmetals from the metals. The elements that have both metallic and nonmetallic properties (semimetals) are shaded in blue. 

The traditional form of the periodic table is shown in Fig. 18.1. Recall that the representative elements, whose chemical properties are determined by the valence-level s and p electrons, are designated Groups 1A through 8A. The transition metals, in the center of the table, result from the filling of d orbitals. The elements that correspond to the filling of the 4/ and 5f orbitals are listed separately as the lanthanides and actinides, respectively. 

The Group 3A elements (valence electron configuration nsznp1) generally show the increase in metallic character in going down the group that is characteristic of the representative elements. Some physical properties, sources, and methods of preparation for the Group 3A elements are summarized in Table 18.9. 

The early chapters in this book deal with chemical reactions. Stoichiometry is covered in Chapters 3 and 4, with special emphasis on reactions in aqueous solutions. The properties of gases are treated in Chapter 5, followed by coverage of gas phase equilibria in Chapter 6. Acid-base equilibria are covered in Chapter 7, and Chapter 8 deals with additional aqueous equilibria. Thermodynamics is covered in two chapters Chapter 9 deals with thermochemistry and the first law of thermodynamics Chapter 10 treats the topics associated with the second law of thermodynamics. The discussion of electrochemistry follows in Chapter 11. Atomic theory and quantum mechanics are covered in Chapter 12, followed by two chapters on chemical bonding and modern spectroscopy (Chapters 13 and 14). Chemical kinetics is discussed in Chapter 15, followed by coverage of solids and liquids in Chapter 16, and the physical properties of solutions in Chapter 17. A systematic treatment of the descriptive chemistry of the representative elements is given in Chapters 18 and 19, and of the transition metals in Chapter 20. Chapter 21 covers topics in nuclear chemistry and Chapter 22 provides an introduction to organic chemistry and to the most important biomolecules. 

To be amenable to investigation by gas chromatography, metal compounds must be volatile and thermally and solvolytically stable at the temperatures necessary for reasonably rapid elution. Many metal chelates of / -diketones have been found to possess these properties and have been successfully chromatographed. Until recently, however, almost all gas chromatographic studies had been limited to complexes of the transition and representative elements because of the paucity of volatile, thermally stable, lanthanide compounds. 

The main-group elements are sometimes called the representative elements because they have a wide range of properties. At room temperature and atmospheric pressure, many are solids, while others are liquids or gases. About half of the main-group elements are metals. Many are extremely reactive, while several are nonreactive. The main-group elements silicon and oxygen account for four of every five atoms found on or near Earth s surface. 

Elements in any given group on the periodic table have the same number of valence electrons. The number and location of valence electrons determine the chemistry of an element. Thus, elements within a group have similar physical and chemical properties. Representative elements display the range of possible valence electrons from one in group lAto eight in group 8A. The valence electrons of representative elements are in s or p orbitals. 

Representative Elements. The A group elements in the periodic table are called representative elements. Their last electron is assigned to an outer shell s or p orbital. These elements show distinct and fairly regular variations in their properties with changes in atomic number. 

Figure 6-8 The normal oxides of the representative elements in their maximum oxidation states. Acidic oxides (acid anhydrides) are shaded red, amphoteric oxides are shaded purple, and basic oxides (basic anhydrides) are shaded blue. An amphoteric oxide is one that shows some acidic and some basic properties.

Compare the extents to which the properties of successive elements across the periodic table differ for representative elements and (/-transition metals. Explain. 

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