Elements chemical definition

All elements, by definition, have a unique proton number, but some also have a unique number of neutrons (at least, in naturally occurring forms) and therefore a unique atomic weight - examples are gold (Au Z = 79, N = 118, giving A =197), bismuth (Bi Z = 83, N = 126, A = 209), and at the lighter end of the scale, fluorine (F Z = 9, N = 10, A = 19) and sodium (Na Z = 11, N= 12, A = 23). Such behavior is, however, rare in the periodic table, where the vast majority of natural stable elements can exist with two or more different neutron numbers in their nucleus. These are termed isotopes. Isotopes of the same element have the same number of protons in their nucleus (and hence orbital electrons, and hence chemical properties), but... 

Gravimetric Analysis, Inorgonic. That branch of quantitative chemical analysis.in which a desired constituent is converted (usually by precipitation) to a pure compd or element of definite, known compn, and is weighed. In a few cases, a compd or element is formed which does not contain the constituent but bears a definite mathematical relationship to it. In either case, the amount of the desired constituent can be detd from the weight and compn of the precipitate. Methods exist for the detn of all the elements by gravimetric analysis... 

The formation of a compound from pure components is independent of the source of the material or of the method of preparation. If elements chemically react to form a compound, they always combine in definite proportions by weight. This concept is known as the Law of Constant Composition. 

Corpuscles might well be divisible, but atoms by definition were not. Today, we associate atoms with chemical elements. Boyle definitely did not do so. That made for difficulties in relating theory to laboratory practice, for reasons we shall soon see. 

Definition of Chemical element Chemical element Chemical element Chemical element... 

Inst as compounds have definite ratios of elements, chemical reactions have definite ratios of reactants and products. Those ratios are used in Section 10.1 to calcnlate the number of moles of other substances in a reaction from the nnm-ber of moles of any one of the snbstances. Section 10.2 combines information from Section 10.1, Chapter 7, and elsewhere to explain how to calcnlate the mass of any substance involved in a reaction from the mass of another. Section 10.3 demonstrates how to work with qnantities in nnits other than moles or masses when finding quantities of reactants or prodncts. Section 10.4 shows how to calcnlate the quantities of snbstances involved in a reaction even if the quantities of reactants present are not in the mole ratio of the balanced equation. Section 10.5 covers the calculation of the percentage yield of a product from the actual yield and the theoretical yield, based on the amonnt(s) of reactant(s). Section 10.6 explains which of these types of calcnlations can and cannot be done with net ionic equations. 

Compounds are substances that are made up of two or more elements chemically combined. The key to this definition is that the elements must be chemically combined. If you physically mix together two elements, let s say iron and copper, you get a mixture, which can be physically separated. Compounds are formed by chemical reactions, where the individual elements lose their individual properties and take on the new properties of the compound that is formed. 

One further interesting development took place in 1932, when Urey discovered isotopes of hydrogen. In these cases, the masses of the isotopes differ from each other by as much as 100% (Urey Grieff, 1935). The properties of these isotopes are definitely not the same. For example water (mostly protium oxide) has a boiling point of 100°C, whereas the value for deuterium oxide is 104°C. Strictly speaking, Fajans had been correct to doubt replaceability, but the problem is only significant in isotopes with very low masses, and Urey s discovery did not change the chemical definition of an element in any way. 

An allotrope of a chemical element is defined as a solid phase (of the pure element) which differs by its crystal structure and therefore by its X-ray diffraction pattern from the other allotropes of that element. This definition can be extended to microcrystalline and amorphous phases which may be characterized either by their diffraction pattern or by suitable molecular spectra. 

Composition A pure substance the simplest building blocks of compounds. A pure substance composed of two or more elements chemically combined in a definite ratio of atoms. Composed of two or more pure substances physically mixed in no particular ratio of substances. 

COMPOUND - They are chemically combined elements with definite proportions of the component elements. 

In chemically reacting mixture 0 (for several reacting constituents at least) due to chemical reactions among reacting constituents. The reactions are described by stoichiometry. Here we follow Bowen [14, 30, 31], see also [12, 48, 65], using non-orthogonal bases (see Appendix A.4) therefore, we use upper or lower indices for contravariant or covariant components. In stoichiometry, we assume that each constituent is composed of atomic substances (atoms—often chemical elements) in definite proportions. The constituent a = 1,..., n is characterized by a positive constant— the molar mass M , which is therefore a linear combination of atomic masses of atomic substances a = 1,2,..., z... 

They could not chemically trace the infinitesimal accumulation of silicon. Joliot explained why in 1935, when he and his wife accepted the Nobel Prize in Chemistry for their discovery The yield of these transmutations is very small, and the weights of elements formed. .. are less than 10 [grams], representing at most a few million atoms —too few to find by chemical reaction alone. But they could trace the radioactivity of the phosphorus with a Geiger counter. If it did indeed signal the artificial transmutation of some of the aluminum to phosphorus, they should be able to separate the two different elements chemically. The radioactivity would go with the new phosphorus and leave the untransmuted aluminum behind. But they needed a definitive separation that could be carried out within three minutes, before the faint induced radioactivity faded below their Geiger counter s threshold. 

The middle of the twentieth century marked the end of a long period of determining the building blocks of chemistry chemical elements, chemical bonds, and bond angles. The lists of these are not definitely closed, but future changes will be more cosmetic than fundamental. This made it possible to go one step further and begin to rationalize the strucmre of molecular systems, as well as to foresee the structural features of the compounds to be synthesized. The crucial concept is based on the Bom-Oppenheimer approximation and on the theory of chemical bonds and resulted in the spatial structure of molecules. The great power of such an approach was first proved by the construction of the DNA double helix model by Watson and Crick. The first DNA model was built from iron spheres, wires, and tubes. 

A compound is a substance that contains two or more elements chemically combined in a definite proportion by mass. 

We often summarize our general observations regarding nature into a statement called a natural law. In the case of the composition of a compound, we use the law of definite composition, which states that a compound always contains two or more elements chemically combined in a definite proportion by mass. 

Chemical compounds are formed by the combination of atoms of different elements in definite, constant ratios that usually can be expressed as integers or simple fractions. 

Chemical compounds are formed by combination of atoms of different elements in definite ratios. 

The middle of the twentieth eentury marked the end of a long period of determining the building blocks of chemistry chemical elements, chemical bonds, bond angles. The hsts of these are not definitely closed, but future changes will be rather cosmetic than fundamental. This made it possible to go one step further and begin... 

Another strand of development came from several attempts to separate some of these new radio-elements chemically, which ended in failure. First of all, in 1907 Herbert McCoy and WiUiam Ross concluded that, in the case of thorium and radiothorium, Our experiments strongly indicate that radiothorium is entirely inseparable from thorium by chemical processes, " a comment Soddy considered the first definitive statement of the chemical inseparability of what were soon to be called isotopes. Soddy himself wrote in the same year that there seemed to be no known method of separating thorium X from mesothorium.They were in fact two isotopes of thorium. Similar cases began to multiply. Bertram Boltwood discovered the radio-element ionium, which could not be chemically separated from thorium. In another famous case, Hevesy and Paneth were asked by Rutherford to try to separate radio-lead from ordinary lead and likewise failed to do so, in spite of using 20 different chemical methods. Their work was not entirely in vain, however, since it led to the development of the use of radioactive tracers, which have become an indispensable tool in modem chemistry and biochemistry. 

In result of reaction the transparent- yellow viscous compoimds well soluble in the usually organic solvents were obtained. Composition and structure of obtained compounds were proved on the basis of elemental analysis, definition of number of epoxy groups and molecular masses and IR spectra. Some physical and chemical data of obtained compounds are presented on the Table 10. 

In numerous experiments Chevreul had analyzed fatty oils of different natural origins. He had isolated from these apparently homogeneous proximate components of animals a whole range of formerly unknown substances, which actually contained their elements in definite proportions. Yet the original natural oils, which had long been identified as chemical species and proximate principles of animals, did not contain their elements in definite proportions. Hence, Chevreul concluded, they were not chemical species but rather mixtures of different substance species. 

As the 1860s drew to a close, the idea of periodicity among the elements was definitely in the air. The first clear statement of the periodic law was made in 1869 by Dmitri Ivanovitch Mendeleev (1834-1907). Mendeleev was an outstanding teacher and possessed a very thorough knowledge of the chemical properties of the elements. Soon after taking up his appointment at the University of St Petersburg,... 

When Proust began his work the constancy of composition of chemical compounds was generally accepted and it formed the basis of the quantitative analytical methods of Bergman (p. 187), Wenzel (p. 671), Kirwan (p. 664) and Richter (p. 681). Lavoisier, although he generally assumed that different compounds formed from two elements were definite in composition, and recognised the existence of two oxides of copper (p. 461), said ... 

Compounds Most substances are compounds. A compound is a substance composed of two or more elements chemically combined. By the end of the eighteenth century, Lavoisier and others had examined many compounds and showed that all of them were composed of the elements in definite proportions by mass. Joseph Louis Proust (1754-1826), by his painstaking work, convinced the majority of chemists of the general validity of the law of definite proportions (also known as the law of constant composition) a pure compound, whatever its source, always contains definite or constant proportions of the elements by mass. For example, 1.0000 gram of sodium chloride always contains 0.3934 gram of sodium and 0.6066 gram of chlorine, chemically combined. Sodium chloride has definite proportions of sodium and chlorine that is, it has constant or definite composition. ... 

Note how atomic theory explains the difference between an element and a compound. Atomic theory also explains two laws we considered earlier. One of these is the law of conservation of mass, which states that the total mass remains constant during a chemical reaction. By postulate 2, every atom has a definite mass. Because a chemical reaction only rearranges the chemical combinations of atoms (postulate 4), the mass must remain constant. The other law explained by atomic theory is the law of definite proportions (constant composition). Postulate 3 defines a compound as a type of matter containing the atoms of two or more elements in definite proportions. 

In spite of all these apparent shortcomings with the Kripke-Putnam causal theory as they apply to the term element , it is not my present task to analyze these problems. The purpose of this article has been to draw parallels between two senses in which the elements may be regarded metaphysically. The purpose has been to also draw parallels between the Mendeleev-Paneth definition of an element as a basic substance on the one hand, and the Kripke-Putnam account of elements as natural kinds on the other hand, both of which approaches deny observable properties to the elements. Finally, the purpose has been to apply the concept of elements as basic substances, which is explicit in the chemical definition and perhaps implicit in the Kripke-Putnam theory of reference, to contemporary issues concerning the placement of certain elements in the periodic system. Of course the overall purpose has been to stimulate further discussion on these issues which lie at the foundations of chemistry. 

The definition of a plasma is an electrically neutral gas made up of positive ions and free electrons. Plasmas have sufficiently high energy to atomize, ionize, and excite virtually all elements in the periodic table, which are intentionally introduced into it for the purpose of elemental chemical analysis. 

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