Pure chemical elements are generally not considered chemical compounds, failing the two or more atom requirement, though they often consist of molecules composed of multiple atoms (such as in the diatomic molecule H 2, or the polyatomic molecule S 8, etc.). Chemical compounds can be molecular compounds held together by covalent bonds, salts held together by ionic bonds, intermetallic compounds held together by metallic bonds, or the subset of chemical complexes that are held together by coordinate covalent bonds. Ĭhemical compounds have a unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds. In the case of non-stoichiometric compounds, the proportions may be reproducible with regard to their preparation, and give fixed proportions of their component elements, but proportions that are not integral. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H 2O.
A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using chemical symbols for the chemical elements, and subscripts to indicate the number of atoms involved. : 15 It follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction, into compounds or substances each having fewer atoms. Īny substance consisting of two or more different types of atoms ( chemical elements) in a fixed stoichiometric proportion can be termed a chemical compound the concept is most readily understood when considering pure chemical substances. Globally, more than 350,000 chemical compounds (including mixtures of chemicals) have been registered for production and use. Many chemical compounds have a unique CAS number identifier assigned by the Chemical Abstracts Service. Non-stoichiometric compounds form a disputed marginal case.Ī chemical formula specifies the number of atoms of each element in a compound molecule, using the standard chemical symbols with numerical subscripts. Molecular compounds are held together by covalent bonds ionic compounds are held together by ionic bonds intermetallic compounds are held together by metallic bonds coordination complexes are held together by coordinate covalent bonds. There are four major types of compounds, distinguished by how the constituent atoms are bonded together. In this process, bonds between atoms may be broken and/or new bonds formed. A compound can be transformed into a different substance by a chemical reaction, which may involve interactions with other substances. A molecule consisting of atoms of only one element is therefore not a compound. The ball-and-stick model of the molecule shows the spatial association of two parts hydrogen (white) and one part(s) oxygen (red)Ī chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. Pure water (H 2O) is an example of a compound.
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