Stoichiometry empirical formulas from

The familiar problem of misleading stoichiometries, and the frequent impossibility of deducing the correct structural formula from the empirical composition is well illustrated by the... 

In the constitutional model of Ugi, rather than molecules, "ensemble of molecules (EM) are used in which the molecules can be either chemically different or identical. Like molecules, an EM has an empirical formula, which is the sum of the empirical formulae of the constiment molecules and describes the collection A of atoms within the EM under consideration. All the EM s which can be formed from A have the same empirical formula . Therefore, an EM(A) consists of one or more molecules which can be obtained from A using each atom which belongs to A only once. Moreover, a FIEM(A) or a family of isomeric EM, is the collection of all EM(A) and it is determined by the empirical formula . On the other hand, a chemical reaction, or a sequence of chemical reactions, is the conversion of an EM into an isomeric EM, and therefore a FIEM contains all EMs which are chemically interconvertible, as far as stoichiometry is concerned. In summary, a FIEM(A) contains, at least in principle, the whole chemistry of the collection A of atoms and since any collection of atoms may be chosen here, Ugi concludes that a theory of FIEM is, in fact, a theory of all chemistry. 

In addition to using the absolute intensities of the atomic emission lines, the peak intensity ratios of these lines have been used to analyze samples. Tran et al. [77] analyzed the atomic intensity ratios of several organic compounds with the hope to determine the empirical formula of a compound based on the ratios from several elements. Calibration curves were built based on C H, C 0, and C N atomic emission ratios from various compounds that covered a wide range of stoichiometries. Then, four compounds with known stoichiometries were tested against the calibration curves. The ratios determined from the calibration curves were compared with the actual stoichiometries and showed accuracy of 3% on average. In the study of nitroaromatic and polycyclic aromatic hydrocarbon samples, the ratios between C2 and CN and between O and N of different samples were shown to correlate with the molecular formula [75], Anzano et al. [71] also attribute success of their correlation of plastics to differences in the C/H atomic emission intensity ratio of each sample. 

The Cu ion is classified as a soft acid (see Hard Soft Acids and Bases), which predicts reasonably well the types of ligands that will be most stabilizing and are, thus, commonly observed in Cu complexes. The preference of Cu for softer ligands is quite apparent in the homoleptic complexes, for instance the halides discussed above. Polynuclear compounds are quite commonly seen in the chemistry of Cn. Thus, the solid-state structure cannot be reliably predicted from the reaction stoichiometry or from the empirical formula of the resulting compound. The careful selection of ligands, for instance, an appropriate macrocyclic ligand can ensnre the formation of a mononuclear complex if one is desired. 

A theoretical model of the combustion of biomass is illustrated by the complete oxidation of giant brown kelp. Note that kelp, for which complete analytical data were available, is used here simply to illustrate the utility of the model, which is applicable to all biomass species. Based on the empirical formula derived from the elemental analysis of dry kelp at an assumed molecular weight of 100, the combustion stoichiometry is... 

It is important to distinguish the stoichiometric or empirical formula of a molecular substance from its molecular formula. The former expresses only the relative numbers of atoms present, in the simplest possible ratio. For example, the compound of stoichiometry P205 contains P401()... 

Boron carbide is often represented as B4C, but this is only a rough empirical formula. The compound is thought to consist of dodecahedral clusters of 12 boron atoms associated with linear rods of 3 carbon atoms, but the stoichiometry is highly variable and can range from BeCs to B4C. Boron carbide is extremely hard (9.3 on the Mohs scale) and is used as an abrasive. 

Elemental analysis is important in establishing the purity and identity of a known compound, or the empirical (stoichiometric) formulae of a new one. Elemental composition is usually quoted as percent by mass, from which the stoichiometry can be determined from atomic mass (RAM) values. Consider a compound (X) with the following composition by mass ... 

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