Element chemical

Now that we have acquired some fundamental ideas about atomic structure, we can more thoroughly discuss the concept of chemical elements. 

All atoms of a particular element have the same atomic number, Z, and, conversely, all atoms with the same number of protons are atoms of the same element. The elements shown on the inside front cover have atomic numbers from Z = 1 to Z = 116. Each element has a name and a distinctive symbol. Chemical symbols are one- or two-letter abbreviations of the name (usually the English name). The first (but never the second) letter of the symbol is capitalized for example, carbon, C oxygen, O neon, Ne and silicon. Si. Some elements known since ancient times have symbols based on their Latin names, such as Ee for iron (ferrum) and Pb for lead (plumbum). The element sodium has the symbol Na, based on the Latin natrium for sodium carbonate. Potassium has the symbol K, based on the Latin kalium for potassium carbonate. The symbol for tungsten, W, is based on the German wolfram. 

Elements beyond uranium (Z = 92) do not occur naturally and must be synthesized in particle accelerators (described in Chapter 25). Elements of the very highest atomic numbers have been produced only on a limited number of occasions, a few atoms at a time. Inevitably, controversies have arisen about 

To represent the composition of any particular atom, we need to specify its number of protons (p), neutrons (n), and electrons (e). We can do this with the symbolism 

This symbolism indicates that the atom is element E and that it has atomic number Z and mass number A. For example, an atom of aluminum represented as 13AI has 13 protons and 14 neutrons in its nucleus and 13 electrons outside the nucleus. (Recall that an atom has the same number of electrons as protons.) 

---

Nesmeyanov, A. N. "Vapor Pressure of the Chemical Elements," Elsevier, New York, 1963. 

Besides stmctural variety, chemical diversity has also increased. Pure silicon fonns of zeolite ZSM-5 and ZSM-11, designated silicalite-l [19] and silicahte-2 [20], have been synthesised. A number of other pure silicon analogues of zeolites, called porosils, are known [21]. Various chemical elements other than silicon or aluminium have been incoriDorated into zeolite lattice stmctures [22, 23]. Most important among those from an applications point of view are the incoriDoration of titanium, cobalt, and iron for oxidation catalysts, boron for acid strength variation, and gallium for dehydrogenation/aromatization reactions. In some cases it remains questionable, however, whether incoriDoration into the zeolite lattice stmcture has really occurred. 

Nowadays, chemical elements are represented in abbreviated form [2]. Each element has its ovm symbol, which typically consists of the initial upper-case letter of the scientific name and, in most cases, is followed by an additional characteristic lower-case letter. Together with the chemical symbol, additional information can be included such as the total number of protons and neutrons in the nucleus, the atomic number (the number of protons in the nucleus) thus isotopes can be distinguished, e.g., The charge value and, finally, the number of atoms which are present in the molecule can be given (Figure 2-3). For example, dioxygen is represented by O2. 

The Wiswesser Line Notation (WLN) was introduced in 1946, in order to organize and to systematically describe the cornucopia of compounds in a more concise manner. A line notation represents a chemical structure by an alphanumeric sequence, which significantly simplifies the processing by the computer [9-11], (n many cases the WLN uses the standard symbols for the chemical elements. Additionally, functional groups, ring systems, positions of ring substituents, and posi-... 

For nearly half a century, Mendeleev s periodic table remained an empirical compilation of the relationship of the elements. Only after the first atomic model was developed by the physicists of the early twentieth century, which took form in Bohr s model, was it possible to reconcile the involved general concepts with the specificity of the chemical elements. Bohr indeed expanded Rutherford s model of the atom, which tried to connect the chemical specificity of the elements grouped in Mendeleev s table with the behavior of electrons spinning around the nucleus. Bohr hit upon the idea that Mendeleev s periodicity could... 

Table 1. Chemical Elements Essential to Healthy Growth of Plants ...

Occurrence in Nature. About 99.6% of the earth s mass results from 32 of the chemical elements. The remaining 0.4% is apportioned among 64 elements, all of which are present as traces. Iodine is one of these 64. Estimates about abundance of the constituent elements of the Hthosphere place iodine 46th on a restricted Hst of 59 elements (37 very rare elements are excluded) and 61st on a Hst in which 96 elements are included. Iodine is, indeed, one of the scarcest of the nonmetaUic elements in the total composition of the earth (3). 

Oxygen usually exhibits a valence of —2 in combination with other chemical elements to form compounds such as oxides. Most elements combine with oxygen, which is highly electronegative, in more than one ratio because of the variety of valences exhibited by the other element, or because of the existence of compHcated molecular stmctures. An extended discussion of oxides is available in the Hterature (13). 

N. V. Sidgwick, Chemical Elements and Their Compounds, Clarendon Press, Oxford, U.K., 1950. 

There are four modes of radioactive decay that are common and that are exhibited by the decay of naturally occurring radionucHdes. These four are a-decay, j3 -decay, electron capture and j3 -decay, and isomeric or y-decay. In the first three of these, the atom is changed from one chemical element to another in the fourth, the atom is unchanged. In addition, there are three modes of decay that occur almost exclusively in synthetic radionucHdes. These are spontaneous fission, delayed-proton emission, and delayed-neutron emission. Lasdy, there are two exotic, and very long-Hved, decay modes. These are cluster emission and double P-decay. In all of these processes, the energy, spin and parity, nucleon number, and lepton number are conserved. Methods of measuring the associated radiations are discussed in Reference 2 specific methods for y-rays are discussed in Reference 1. 

There are numerous misconceptions about the sources of various chemical elements in waste, particularly those that are potential acid formers when the waste is incinerated or mechanically converted and used as a refuse-derived fuel. For example, it is often mistakenly stated that the source of chlorine in waste, hence a potential source of HCl emissions, is poly(vinyl chloride). The relative contents of selected, potentially acid-forming elements in the organic portion of a sample of waste collected from various households in one U.S. East Coast city is given in Table 2 (17). In this city, a chief source of chlorine in the waste is NaCl, probably from food waste. 

Silicon, a low density chemical element having nonmetallic chaiacteristics, is the second, after oxygen (50.5%), most abundant element in the lithosphere. Silicon occurs naturally in the form of oxides and silicates and constitutes over 25% of the earth s cmst (see Silica). 

It was not until the eighteenth century that carbon was recognized as a chemical element, and it is quite certain that no early metallurgist was aware of the basis of the unique properties of steel as compared to those of wrought iron. Carbon can be alloyed with iron in a number of ways to make steel, and all methods described herein have been used at various times in many locaUties for perhaps 3000 or more years. 

The physical and mechanical properties of steel depend on its microstmcture, that is, the nature, distribution, and amounts of its metaHographic constituents as distinct from its chemical composition. The amount and distribution of iron and iron carbide determine most of the properties, although most plain carbon steels also contain manganese, siUcon, phosphoms, sulfur, oxygen, and traces of nitrogen, hydrogen, and other chemical elements such as aluminum and copper. These elements may modify, to a certain extent, the main effects of iron and iron carbide, but the influence of iron carbide always predominates. This is tme even of medium alloy steels, which may contain considerable amounts of nickel, chromium, and molybdenum. 

Analytical x-ray instruments ate used to characterize materials in several different ways. As with medical x-ray instmments there are analytical instmments that can produce images of internal stmctures of objects that are opaque to visible light. There are instmments that can determine the chemical elemental composition of an object, that can identify the crystalline phases of a mixture of soHds, and others that determine the complete atomic and molecular stmcture of a single crystal. These ate the most common appHcations for x-ray iastmments. 

Many chemical elements exhibit catalytic activity (5) which, within limits, is inversely related to the strength of chemisorption of the VOCs and oxygen, provided that adsorption is sufficiently strong to achieve a high surface coverage (17). If the chemisorption is too strong, the catalyst is quickly deactivated as the active sites become irreversibly covered. If the chemisorption is too weak, only a small fraction of the surface is covered and the activity is very low (17) (Fig. 2). 

To isolate a system for study, the system is separated from the surroundings by a boundary or envelope that may either be real (e.g., a reactor vessel) or imaginary. Mass crossing the boundaiy and entering the system is part of the mass-in term. The equation may be used for any compound whose quantity does not change by chemical reaction or for any chemical element, regardless of whether it has participated in a chemical reaction. Furthermore, it may be written for one piece of equipment, several pieces of equipment, or around an entire process (i.e., a total material balance). 

---