Element : Definition

An element is a chemical substance in which atoms form a unique species of one type of atom and cannot be further broken down into simpler chemicals by physical separation or chemical reactions. An atom of an element has a defined number of protons that is referred to as the atomic number (symbol Z) of that element. Thus isotopes of an element, in having the same number of protons and differing in the number of neutrons, are also of the same element. The number of protons is rigid, so that the species is still identified as the element in an ionised form or when combined with other elements in a molecule. When a proton is lost, such as through radiation decay (nuclear fission) or subatomic bombardment, the element becomes identified by the resulting new atomic number. Nuclear fusion is another way the atomic number can change.

The term element also applies to pure chemicals composed of a single element (e.g. H₂) or allotropes of the element (e.g. O₂ and O₃), although the term allotrope is generally kept at some distance from being the same as being an element.

Published on: 29 Dec 2017 at 1758.
Last updated: 29 Dec 2017 at 1758.