Chemical element

A chemical element is the simplest possible kind of chemical substance, in that it cannot be broken down into simpler substances by chemical means. In this way, chemical elements are distinguished from chemical compounds, which consist of two or more elements. There are 112 chemical elements which are generally accepted, of which 94 occur naturally on the Earth, and another six whose preparation has been claimed and is awaiting confirmation. Common examples of chemical elements include oxygen, nitrogen, sulfur, iron, copper and gold.

The atoms of a given chemical element all contain the same number of protons in their nuclei. This number is called the atomic number of the element. The neutral atoms will also contain the same number of electrons around the nucleus, which determine the chemistry of the element. The elements are often ordered by increasing atomic number in the periodic table, which emphasizes similarities and regular trends in the chemistries of the different elements.

It is a general tenet of chemistry that elements cannot be transformed into one another. This is not completely true, as radioactive decay and other nuclear reactions can transform atoms of one element into atoms of another element, but it is a good enough approximation for virtually all chemistry. The energies involved in nuclear reactions are very much higher than those of chemical reactions, and so nuclear reactions usually form a separate field of study. Nevertheless, such nuclear reactions, especially in stars and supernovae, are responsible for the formation of most elements in the first place.

See also

• Atomic weights of the elements 2007
• Physical and thermochemical properties of the elements
• Electric resistivities of the elements