Chemical Element

A chemical element is a substance that cannot be broken down by ordinary chemical means, consisting of atoms that all have the same number of protons in the nucleus. This number of protons is called the atomic number and determines which element an atom belongs to.

Elements make up all tangible matter. When two or more elements bond chemically, they form a compound, such as water, which consists of hydrogen and oxygen. Separating compounds requires chemical processes, whereas elements can be separated only by nuclear means.

Atomic Number and Isotopes

The number of protons in the nucleus identifies an element. The number of neutrons may vary: atoms of the same element but with different numbers of neutrons are called isotopes. Isotopes of the same element have similar chemical properties but different mass and nuclear stability. Some isotopes are radioactive, meaning their nucleus decays and transforms into a different element.

The Periodic Table

Elements are arranged in a table called the periodic table, ordered by increasing atomic number. Elements in the same group (column) typically share similar chemical properties because they have the same electron configuration in their outer shell. This system was originally presented by Dmitri Mendeleev in the 19th century and has been refined with advances in atomic structure theory.

Classification and Properties

Elements are classified as metals, nonmetals, and metalloids. Metals conduct electricity and heat and are malleable. Each element is identified by a symbol, such as H (hydrogen), O (oxygen), Fe (iron), Au (gold). These symbols derive from Latin names or established international nomenclature.

Origins of Elements

Light elements, particularly hydrogen and helium, come from the early state of the universe. Heavier elements are formed in the interiors of stars and in stellar explosions (supernovae). The heaviest elements are produced only in neutron stars and decay very rapidly.