Elements in compounds

Stoichiometry is the discipline that deals with the amount relationships of the elements in compounds and during chemical reactions. It is not the amount relationship itself. A specific compound has no stoichiometry, but a composition. 

In cases where elements in compounds retain unused exposed electrons, especially those in pairs, they occupy space and are stereochemically active. They are often sites of reaction. 

This is why SN2 type of displacements are more facile at the silicon atom than at the carbon. This is particularly so with nucleophiles derived from the more electronegative element. In compounds of the type of R3SiX (where X = leaving group), the nucleophilic displacements and hydrolysis in aqueous media occur rapidly. 

Lithium ranks 33rd among the most abundant elements found on Earth. It does not exist in pure metallic form in nature because it reacts with water and air. It is always combined with other elements in compound forms. These lithium mineral ores make up only about 0.0007%, or about 65 ppm, of the Earth s crust. 

Substances resulting from the chemical combination of two or more elements in fixed proportions are called compounds. The elements in compounds are chemically bonded to each other. Most elements do not exist in their free native state but are found in combination with other elements as chemical compounds. Compounds may exist as ionic compounds or molecular compounds. In ionic compounds, the constituent elements exist as ions. Ions are atoms or groups of atoms that carry a charge by virtue of losing or gaining one or more electrons. 

Table 6.3 ions Negative oxidation states of Group 15-17 elements in compounds and ... 

The following are references to the estimation of tellurium in organic compounds Lyons and Bush, J. Amer. Chem. Soc., 1908, 30, 831 Morgan and Drew, Tram. Chem. 180c., 1920, 117, 1463 Drew, J. Chem. Soc., 1926, p. 3054. The last-mentioned deals with the estimation of the element in compounds containing tellurium and sulphur. 

Compounds have no charge overall. Hence the oxidation states of all the individual elements in a compound must add up to 0. The oxidation states of elements in compounds can vary, as seen in Table 3.6. It is possible to recognise which of the different oxidation states a metal element is in by the colour of its compounds (Figure 3.18). 

So far we have considered pure substances of atoms that can join up with bonds to form molecules, which can contain atoms of the same element (e.g. H2 or 02) or atoms of different elements in compounds (e.g. H20, C02, CH4). 

In this chapter, you have learned about the relationships among the number of particles in a substance, the amount of a substance in moles, and the mass of a substance. Given the mass of any substance, you can now determine how many moles and particles make it up. In the next chapter, you will explore the mole concept further. You will learn how the mass proportions of elements in compounds relate to their formulas... 

In this chapter, you will learn about the relationships between chemical formulas, molar masses, and the masses of elements in compounds. 

It has been confirmed that elements in compounds in organic solvents usually give the same response in electrothermal atomisation as the same element in an aqueous standard solution. This is because the solvent is removed at the drying stage and most organic complexes are converted to stable inorganic compounds at low ashing temperatures. 

Descibes the quantitative (mass) relationships among elements in compounds. Compound... 

Lavoisier discovered the law of conservation of matter, which states that matter cannot be created or destroyed during chemical reactions or physical changes. This generalization increased chemists efforts to measure the masses of elements in compounds and resulted in two more laws. The law of definite proportions states that the percentage of each element in any sample of a pure compound is always the same. According to the law of multiple proportions, if the mass of one of the elements in two or more compounds of the same elements is held constant, the masses of each other element form a small, whole-number ratio. (Section 3.1)... 

Rules for writing diatomic molecules and for deducing the charges on alkali metal ions were introduced in this chapter. Which of these refers only to uncombined elements and which refers only to elements in compounds ... 

The presence of what element most commonly results in basic properties for an organic compound What is present on this element in compounds that allows it to accept a proton ... 

---