Chemical properties elements

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. 

The values given in the following table for the heats and free energies of formation of inorganic compounds are derived from a) Bichowsky and Rossini, Thermochemistry of the Chemical Substances, Reinhold, New York, 1936 (h) Latimer, Oxidation States of the Elements and Their Potentials in Aqueous Solution, Prentice-Hall, New York, 1938 (c) the tables of the American Petroleum Institute Research Project 44 at the National Bureau of Standards and (d) the tables of Selected Values of Chemical Thermodynamic Properties of the National Bureau of Standards. The reader is referred to the preceding books and tables for additional details as to methods of calculation, standard states, and so on. 

Arguably, however, Mendeleev s greatest achievement was not the periodic table so much as the recognition of the periodic system on which it was based. Of the nearly 1,000 variations that have been published since, all are attempts to represent the fundamental rule that after certain but varying intervals, the chemical elements show an approximate repetition in their properties. 

It graces the walls of lecture halls and laboratories of all types, from universities to industry. It is one of the most powerful icons of science. It captures the essence of chemistry in one elegant pattern. The periodic table provides a concise way of understanding how all known chemical elements react with one another and enter into chemical bonding, and it helps to explain the properties of each element that make it react in such a fashion. 

But what would become of Mendeleev s periodic system which now seemed to consist of 300 or so "elements" To some chemists, the discovery of isotopes implied the end of the periodic system as it was known.3 These chemists suggested that it would be necessary to consider the individual new isotopes as the new "elements." But the chemist Paneth adopted a less reductionist approach, arguing that the periodic table of the familiar chemical elements should be retained because it dealt with the "elements" that were of interest to chemists. A justification for this view was provided by the fact that, with a few exceptions, the chemical properties of isotopes of the same element are indistinguishable.4 Moreover, Paneth appealed to Mendeleev s distinction between the two senses of the concept of an "element" in order to provide a philosophical rationale for the retention of the chemist s periodic table. Paneth argued that the discovery of isotopes of the elements represents the discovery of new elements as simple substances, whereas periodic... 

Schumm, R.H. Wagmann, D.D. Bailey, S. Evans, W.H. Parker, V.B. "Selected Values of Chemical Thermodynamic Properties" -Table for Lanthanide Elements", NBS-Technical Note 270-7, U.S. Govt. Printing Office, 1973. 

Which property—the atomic mass or atomic number—uniquely identifies a chemical element Explain how the property uniquely identifies each atom. 

The defining characteristic of an atom of a chemical element is the number of protons in its nucleus. A given element may have different isotopes, which are nuclei with the same numbers of protons but different numbers of neutrons. For example, 12C and 14C are two isotopes of carbon. The nuclei of both isotopes contain six protons. However, 12C has six neutrons, whereas 14C has eight neutrons. In general, it is the number of protons and electrons that determines chemical properties of an element. Thus, the different isotopes of an element are usually chemically indistinguishable. These isotopes, however, have different masses. 

Chemical Elements and Their Properties AN1) Name/Symbol Atomic weight... 

Molecules, the smallest units of matter that have the properties of a substance, are made up of two or more atoms. The molecules of some chemical elements, such as oxygen and nitrogen, mentioned above, for example, are made up of two identical atoms. The molecules of compounds, that consist of two or more combined elements are made up two or more atoms of different elements bonded together (see Textbox 2). 

A number of chemical elements, mainly oxygen and carbon but also others, such as tin, phosphorus, and sulfur, occur naturally in more than one form. The various forms differ from one another in their physical properties and also, less frequently, in some of their chemical properties. The characteristic of some elements to exist in two or more modifications is known as allotropy, and the different modifications of each element are known as its allotropes. The phenomenon of allotropy is generally attributed to dissimilarities in the way the component atoms bond to each other in each allotrope either variation in the number of atoms bonded to form a molecule, as in the allotropes oxygen and ozone, or to differences in the crystal structure of solids such as graphite and diamond, the allotropes of carbon. 

The 92 chemical elements that occur naturally in the earth can be divided into two main groups metals and nonmetals. Although the distinction between the two is not always sharp and clear, it can be said that over 70 of the 92 elements are metals among the fewer than 22 remaining non-metals, six are known as metalloids, which have properties that fall between those of metals and nonmetals (see Appendix I). 

In common parlance, the term metal is used to refer to two different types of metallic materials metals and alloys. The metals are chemical elements each metal (e.g., copper, iron, and gold) is composed of only one type of atom. The alloys are mixtures that have metallic properties. All alloys include two or more elements in their composition some are made up of two or more metals, others of one or more metals mixed with one or more nonmetals. Bronze, for example, is made up of two metals copper (60-85%) and tin (40-15%) steel includes iron, a metal (98-99.97%) and carbon, a nonmetal (2-0.03%). Metals and alloys share many common properties ... 

Knowledge of the 90 chemical elements and their properties in compounds led to the construction, by man, of a unique table of elements, the Periodic Table, of 18 Groups in six periods in a pattern fully explained by quantum theory, described in Chapter 2. There is then a huge variety of chemical combinations possible on the Earth and limitations on what is observable are related to element position in this Table. It also relates to the thermodynamic and/or kinetic stability of particular combinations of them in given physical circumstances (Table 11.3). The initial state of the surface of the Earth with which we are concerned was a dynamic water layer, the sea, covering a crust mainly of oxides and some sulfides and with an atmosphere of NH3, HCN, N2, C02(C0, CH4), H20, with some H2 but no 02. This combination of phases and their contents then produced an aqueous solution layer of particular components in which there were many concentration restrictions between it and the components of the other two layers due to thermodynamic stability, equilibria, or kinetic stability of the chemicals trapped in the phases. It is the case that equilibrium... 

These properties of soils in Steppe ecosystems are favorable to the formation of uppermost humus barrier, where the accumulation of almost all the chemical species occur. The concentration of chemical elements is slightly decreasing downward in soil profile, in parallel with decreasing soil humus content (Figure 2). 

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