What Is an Element in Chemistry? Definition and Examples

What Is an Element in Chemistry?

Periodic Table of Elements
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Element Definition

A chemical element is a substance that cannot be broken down by chemical means. Although elements aren't changed by chemical reactions, new elements may be formed by nuclear reactions.

Elements are defined by the number of protons they possess. Atoms of an element all have the same number of protons, but they can have different numbers of electrons and neutrons. Changing the ratio of electrons to protons creates ions, while changing the number of neutrons form isotopes.

There are 115 known elements, although the periodic table has space for 118 of them. Elements 113, 115, and 118 have been claimed, but require verification to earn a place on the periodic table. Research is also underway to make element 120. When element 120 is made and verified, the periodic table will need to be changed to accommodate it!

Examples of Elements

Any of the types of atoms listed on the periodic table is an example of an element, including:

  • copper
  • cesium
  • iron
  • neon
  • krypton
  • proton - technically a lone proton qualifies as an example of the element hydrogen

Examples of Substances That Are Not Elements

If more than one type of atom is present, a substance is not an element. Compounds and alloys are not elements. Similarly, groups of electrons and neutrons are not elements. A particle must contain protons to be an example of an element. Non-elements include:

  • water (composed of hydrogen and oxygen atoms)
  • steel
  • electrons
  • brass (composed of multiple types of metal atoms)