What Is a Chemical Element?

Chemical Elements and Examples

Gold sometimes occurs in nature as a pure element.
This is a natural gold crystal. Gold sometimes occurs in nature as a pure element. John Cancalosi, Getty Images

A chemical element, or an element, is defined as a material which cannot be broken down or changed into another substance using chemical means. Elements may be thought of as the basic chemical building blocks of matter. There are 118 known elements. Each element is identified according to the number of protons it has in its atomic nucleus. A new element may be created by adding more protons to an atom.

Atoms of the same element have the same atomic number or Z.

Element Names and Symbols

Each element may be represented by its atomic number or by its element name or symbol. The element symbol is a one or two letter abbreviation. The first letter of an element symbol is always capitalized. A second letter, if it exists, is written in lower case. The International Union of Pure and Applied Chemistry (IUPAC) has agreed on a set of names and symbols for the elements, which are used in scientific literature. However, the names and symbols for the elements may be different in common use in various countries. For example, element 56 is called barium with element symbol Ba by the IUPAC and in English. It is called bario in Italian and baryum in French. Element atomic number 4 is boron to the IUPAC, but boro in Italian, Portuguese, and Spanish, Bor in German, and bore in French. Common element symbols are used by countries with similar alphabets.

Element Abundance

Of the 118 known elements, 94 are known to occur naturally on Earth. The others are called synthetic elements. The number of neutrons in an element determines its isotope. 80 elements have at least one stable isotope. Thirty-eight consist solely of radioactive isotopes which decay over time into other elements, which may be either radioactive or stable.

On Earth, the most abundant element in the crust is oxygen, while the most abundant element in the entire planet is believed to be iron. In contrast, the most abundant element in the universe is hydrogen, followed by helium.

Element Synthesis

Atoms of an element may be produced by the processes of fusion, fission, and radioactive decay. All of these are nuclear processes, which means they involve the protons and neutrons in the nucleus of an atom. In contrast, chemical processes (reactions) involve electrons and not nuclei. In fusion, two atomic nuclei fuse to form a heavier element. In fission, heavy atomic nuclei split to form one or more lighter ones. Radioactive decay can produce different isotopes of the same element or a lighter element.

When the term "chemical element" is used, it can refer to a single atom of that atom or to any pure substance consisting only of that type of iron. For example, an iron atom and a bar of iron are both elements of the chemical element.

Examples of Elements

  • Hydrogen
  • Gold
  • Sulfur
  • Oxygen
  • Uranium
  • Iron
  • Argon
  • Americium
  • Tritium (an isotope of hydrogen)

Examples of Substances That Are Not Elements

  • Brass
  • Water
  • Air
  • Plastic
  • Fire
  • Sand