Stoichiometry compound

The concept of a structure-field map (1) has proven useful in systematizing the occurrence of different structures among a range of fixed-stoichiometry compounds of the A yO type studied here. A binary phase diagram is constructed in which the axes represent the crystal radii (2) of the A and B ions, r and rg, for the appropriate near-neighbor configuration. 

Oxidation States Compounds are formed with elements in the group oxidation state up to Mn, higher states being found mostly with oxides and fluorides. Lower oxidation states are more stable for later elements. Many mixed-valency and non-stoichiometry compounds are known. 

Pure stoichiometric CeOj has the calcium fluoride (fluorite) type of structure with space group / m3m. It has been also well known as a Non-stoichiometri compound and there are variety of studies concerning about the defect and redox chemistry [17-19]. Among them, Stefano has already reported the electron localization in pure and defective ceria by a unified LDA+U approach as shown in Figure 4-9 [20]. Here we can see the decrease of band gap of both cerium sub oxide... 

The increase of the number of atoms in the formula unit allows another ordering of the particles of AB stoichiometry compounds. Such instance is possible due to the fact that the atom of B-type can have different coordination. This arrangement is illustrated by the BiLi3 structure. 

L.S.Fetterly. In Non-Stoichiometrie Compounds. Ed. hy L.Mandelcorn. Acad.Press. New York-London, 196 1. 

Note The numbers nand m refer to the stoichiometry compound Ce 02 2 . 

In empirical formulas of inorganic compounds, electropositive elements are listed first [3]. The stoichiometry of the element symbols is indicated at the lower right-hand side by index numbers. If necessary, the charges of ions are placed at the top right-hand side next to the element symbol (e.g., S "). In ions of complexes, the central atom is specified before the ligands are listed in alphabetical order, the complex ion is set in square brackets (e.g., Na2[Sn(OH)+]). 

The elements of an organic compound are listed in empirical formulas according to the Hill system [8] and the stoichiometry is indicated by index numbers. Hill positioned the carbon and the hydrogen atoms in the first and the second places, with heteroatoms following them in alphabetical order, e.g., C9H11NO2. However, it was recognized that different compounds could have the same empirical formula (see Section 2.8.2, on isomerism). Therefore, fine subdivisions of the empirical... 

An additional problem is encountered when the isolated solid is non-stoichiometric. For example, precipitating Mn + as Mn(OH)2, followed by heating to produce the oxide, frequently produces a solid with a stoichiometry of MnO ) where x varies between 1 and 2. In this case the nonstoichiometric product results from the formation of a mixture of several oxides that differ in the oxidation state of manganese. Other nonstoichiometric compounds form as a result of lattice defects in the crystal structure. ... 

Quantitative Calculations When needed, the relationship between the analyte and the analytical signal is given by the stoichiometry of any relevant reactions. Calculations are simplified, however, by applying the principle of conservation of mass. The most frequently encountered example of a direct volatilization gravimetric analysis is the determination of a compound s elemental composition. 

In a gravimetric analysis a measurement of mass or change in mass provides quantitative information about the amount of analyte in a sample. The most common form of gravimetry uses a precipitation reaction to generate a product whose mass is proportional to the analyte. In many cases the precipitate includes the analyte however, an indirect analysis in which the analyte causes the precipitation of another compound also is possible. Precipitation gravimetric procedures must be carefully controlled to produce precipitates that are easily filterable, free from impurities, and of known stoichiometry. 

Prior to methanation, the gas product from the gasifier must be thoroughly purified, especially from sulfur compounds the precursors of which are widespread throughout coal (23) (see Sulfurremoval and recovery). Moreover, the composition of the gas must be adjusted, if required, to contain three parts hydrogen to one part carbon monoxide to fit the stoichiometry of methane production. This is accompHshed by appHcation of a catalytic water gas shift reaction. 

Citrates. Iron citrate [2338-05-8] is a compound that contains citric acid and iron(II) and iron(III) in indefinite ratios. Iron(II) citrate [23383-11-1] and iron(III) citrate [28633-45-6] are also of indefinite stoichiometry, although iron(III) citrate which contains Fe and citric acid in a 1 1 ratio [3522-50-7] is known. These compounds dissolve slowly in water and are more readily soluble in hot water. The solution chemistry of these compounds is comphcated by formation of a number of monomeric and oligomeric species. All of the iron citrate compounds are used as supplements to soils and animal diets. 

Iron(III) ammonium citrate [1185-57-5] is of indefinite stoichiometry. A brown hydrated compound [1332-98-5] of iron(III) ammonium citrate contains 16.5—18.5% iron, - 9% ammonia, and 65% citric acid. A green hydrated compound [1333-00-2] contains 14.5—16% iron, 1% ammonia, and 75% citric acid. Iron ammonium citrates are water soluble but are insoluble in alcohol. The compounds are used to fortify bread, milk, and other foods (see... 

Most of these compounds react readily with available oxygen, including H2O. These compounds have simple stoichiometries, iategral values of x,y, and exhibit conductivities ranging from iasulatiag to metal-like. 

Phosphides. Compounds of phosphoms containing the more electropositive elements are generally called phosphides. A large number of binary phosphides as well as many ternary mixed-metal phosphides, metal phosphide nitrides, etc, are known. Some binary phosphides, such as those of nickel, exhibit a variety of stoichiometries (Ni P, Ni P2, Nq2P5, Ni2P, Ni P, NiP, NiP2, NiP ), whereas others, such as aluminum, form only one (AlP). Metalloids such as B and Si also form phosphides. 

The most significant difference between the alkoxysilanes and siUcones is the susceptibiUty of the Si—OR bond to hydrolysis (see Silicon compounds, silicones). The simple alkoxysilanes are often operationally viewed as Hquid sources of siUcon dioxide (see Silica). The hydrolysis reaction, which yields polymers of siUcic acid that can be dehydrated to siUcon dioxide, is of considerable commercial importance. The stoichiometry for hydrolysis for tetraethoxysilane is... 

The reactions of thionyl chloride with organic compounds having hydroxyl groups are important. Alkyl chlorides, alkyl sulfites, or alkyl chlorosulfites form from its reaction with aUphatic alcohols, depending on reaction conditions, stoichiometry, and the alcohol stmcture ... 

---