<P> An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction . This is so, because all of the atoms in a sample of an element have the same number of protons, though they may be different isotopes, with differing numbers of neutrons . </P> <P> As of 2012, there are 118 known elements, about 80 of which are stable--that is, they do not change by radioactive decay into other elements . Some elements can occur as more than a single chemical substance (allotropes). For instance, oxygen exists as both diatomic oxygen (O) and ozone (O). The majority of elements are classified as metals . These are elements with a characteristic lustre such as iron, copper, and gold . Metals typically conduct electricity and heat well, and they are malleable and ductile . Around a dozen elements, such as carbon, nitrogen, and oxygen, are classified as non-metals . Non-metals lack the metallic properties described above, they also have a high electronegativity and a tendency to form negative ions . Certain elements such as silicon sometimes resemble metals and sometimes resemble non-metals, and are known as metalloids . </P> <P> A pure chemical compound is a chemical substance that is composed of a particular set of molecules or ions . Two or more elements combined into one substance through a chemical reaction form a chemical compound . All compounds are substances, but not all substances are compounds . </P> <P> A chemical compound can be either atoms bonded together in molecules or crystals in which atoms, molecules or ions form a crystalline lattice . Compounds based primarily on carbon and hydrogen atoms are called organic compounds, and all others are called inorganic compounds . Compounds containing bonds between carbon and a metal are called organometallic compounds . </P>

A process in which at least one new substance is produced as a result of chemical change