Chemical formulas definition

CRS provides information on chemical substances and how they are represented in the Environmental Protection Agency regulations and data systems. A search engine for chemicals by CAS number, name, molecular formula, chemical type, definition, or other data identifiers. 

As the value of these two new chemicals for insecticides became more evident, the need for extended experimental and test work was definitely established. It was necessary to determine chemical formulas, work out analytical methods, obtain knowledge of various physical and chemical characteristics, and complete evaluation of insecticidal action as well as toxicity and effect of residues. Toxicity was concerned with not only insects but humans and other warm-blooded animals. Residual studies included information on persistence and type and amount of residue. This information, once accumulated, must be correlated with similar information on other insecticides. 

CHEMICAL FORMULAS. Chemistry definitions may include either an empirical formula (say, for abietic acid, C20H30O2) or a line formula (for acrylonitrile, CH2CHCN), whichever is appropriate. 

For definitions of units, chemical composition of minerals, chemical formulae of molecules and time spans of geologic periods, see the Appendices. 

Solid phases of binary systems, like the liquid phases, are very commonly of variable composition. Here, as with the liquid, the stable range of composition is larger, the more similar the two components are. This of course is quite c-ontrary to the chemists notion of definite chemical composition, definite structural formulas, etc., but those notions are really of extremely limited application. It happens that the solid phases in the system water—ionic compound are often of rather definite composition, and it is largely from this rather special case that the idea of definite compositions in solids has become so firmly rooted. In such a system, there are normally two solid phases ice and the crystalline ionic compound. Ice can take up practically none of any ionic compound, so that it has practically no range of compositions. And many ionic crystals... 

Except where the context requires otherwise, the term refers to a set of -> molecular entities containing isotopes in their natural abundance. The wording of the definition given in the first paragraph is intended to embrace both cases, such as graphite, sodium chloride, or a surface oxide, where the basic structural units may not be capable of isolated existence, as well as those cases where they are. In common chemical usage, generic and specific chemical names (such as -> radical or hydroxide ion) or chemical formulae refer either to a chemical species or to a molecular entity. 

Arrhenius s definition of acids and bases is the definition that most people know. Acids can be recognized because their chemical formulas have an H at the beginning, like HBr and HN03. Bases are easy to recognize because their chemical formulas end with OH, like NaOH or KOH. There are a few strong acids and bases that you should be familiar with. These strong acids and bases ionize completely in solution and dissociate into as many hydro-nium ions and hydroxide ions as are available. 

The problem of the nature of the potential-determining ions is very complex and in many cases has not been solved definitively, therefore the chemical formulas of micelles often are tentative in character. 

The law of definite proportions tells us that our ingredients have a specific chemical formula for example, H2O is the chemical formula for water. In essence, the chemical formula consists of a list of the elements that built the substance and the numbers of atoms of each that were required. There are subtleties, however, in the arrangement of elements, just as there are subtleties in the arrangement of elements in the periodic table. More information can be gleaned from the chemical formula than just the number and type of components. 

The law of definite proportions states simply that the formula for any one material is set and invariable. Any change to the chemical formula... 

The oxidation numbers of ions are used to determine the formulas for the ionic compounds they form. Recall that in ionic compounds, oppositely charged ions combine chemically in definite ratios to form a compound that has no charge. If you add the oxidation number of each ion multiplied by the number of these ions in a formula unit, the total must be zero. 

The law of definite proportions was a crucial step in the development of modern chemistry, and by 1808, Proust s conclusions had become widely accepted. We now recognize that this law is not strictly true in all cases. Although all gaseous compounds obey Proust s law, certain solids exist with a small range of compositions and are called nonstoichiometric compounds. An example is wiistite, which has the nominal chemical formula FeO (with 77.73% iron by mass), but the composition of which, in fact, ranges continuously from Feo.950 (with 76.8% iron) down to Fco.siO (74.8% iron), depending on the method of preparation. Such compounds are called berthollides, in honor of Berthollet. We now know, on the atomic level, why they are nonstoichiometric (see the discussion in Section 21.6). 

So far, we have identified coordination compounds only by their chemical formulas, but names are also useful for many purposes. Some substances were named before their structures were known. Thus, K3[Fe(CN)g] was called potassium fer-ricyanide, and K4[Fe(CN)g] was potassium ferrocyanide [these are complexes of Fe (ferric) and Fe (ferrous) ions, respectively]. These older names are still used conversationally but systematic names are preferred to avoid ambiguity. The definitive source for the naming of inorganic compounds is Nomenclature of Inorganic Chemistry-IUPAC Recommendations 2005 (N. G. Connelly and T. Damhus, Sr., Eds. Royal Society of Chemistry, 2005). 

In addition to the monographs, the BP contains a section on General Notices, printed at the beginning of each volume on coloured paper. These notices include important definitions (e.g. recently prepared), and data on subjects such as solubility (freely, sparingly, etc.), storage conditions, labelling requirements, chemical formulae, as well as cross references to the European Pharmacopoeia (EP) produced in Strasbourg. 

The success of the preceding scheme for diatomic molecules I7,i8,i , 20,21) ied Hund 22> and Mulliken 23> to apply the same theory to polyatomic molecules. In the beginning, there seemed to be no direct relation between molecular orbitals (MO s) and the bonds in a chemical formula, because MO s normally extend over the whole molecule and are not restricted to the region between two atoms. The difficulty was overcome by using equivalent localized MO s instead of the delocalized ones 24>25>. The mathematical definition of equivalent MO s was given only in 1949 by Lennard-Jones and his coworkers 26.27), but the concept of localization... 

Definitions. Afj s fk designates a system with respect to its chemical formula f and location (reactor) k in the flow system. The system is a fluid element containing F chemical species for which f = 1, 2, 3,. F where each figure designates a certain species with its chemical formula. In addition, k = a, b,. Z, where each letter designates a reactor in the flow system composed of Z + 1 perfectly mixed reactors, including reactor... 

Definition The extent of a chemical reaction is one unit of file chemical formula selected. 

The subscript des in the definitions refers to the chemical formula that ties reactant A to the product V (the desirable reaction). In some cases (e.g., in sequential reactions) the desirable reaction does not actually take place, but rather it is merely stoichiometric relations (see Example 2.11). 

Elements and Compounds—Chemical Symbols—Molecules—Atoms —Electrons—How Electrons Form Atoms—Explanation of Chemical Activity—Chemical Formulas—Speed of Chemical Reactions—Physical and Chemical Changes—The Law of Definite Proportions—Different Kinds of Chemical Reaction —Classification of Chemical Compounds—The Law of Combining Weights—Solutions—Acids and Bases—Neutral Substances—Organic and Inorganic Chemistry—Electrochemistry —Experiments in Electrochemistry, Pages 7-39... 

---