A chemical element (sometimes called simply element) is a class of atoms with the same number of protons in the nucleus. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium.
In the bulk phase, a pure element consists of only one kind of atom. Atoms of the same element whose nuclei contain a different number of neutrons are said to be different isotopes of the element. A pure element can sometimes exist in different arrangements. These are called allotropes. Chemical elements are commonly arranged in the periodic table.
The official names of the chemical elements are decided by the International Union of Pure and Applied Chemistry. Chemical elements are also given a unique chemical symbol, often based on the name of the element, though possibly not in English (for example, carbon has chemical symbol 'C', and sodium has chemical symbol 'Na' after the Latin natrium). Chemical symbols are understood internationally when element names might need to be translated.
See also discovery of the chemical elements