What Is an Element in Chemistry? Definition and Examples

Element Definition and Periodic Table
An element is defined as a pure substance consisting of atoms with the same number of protons. There are 118 elements that are ordered by increasing atomic number (number of protons) on the periodic table.

In chemistry, an element is defined as a pure substance composed of atoms that all have the same number of protons in the atomic nucleus. In other words, all atoms of an element have the same atomic number. The atoms of an element (sometimes called “chemical element”) cannot be broken into smaller particles by any chemical means. Elements can only be broken into subatomic particles or transmuted into other elements by nuclear reactions. At present, there are 118 known elements.

If atoms of an element carry an electrical charge, they are called ions. Atoms of an element with different numbers of neutrons are called isotopes. Sometimes isotopes also have their own names, but they are still examples of an element. For example: protium, deuterium, and tritium are all isotopes of the element hydrogen. Elements can take different forms called allotropes, but this doesn’t change their chemical identity. For example: diamond and graphite are both pure elemental carbon.

Examples of Elements

Any of the 118 elements on the periodic table is an example of any element. Because elements are defined by the number of protons, any isotopes, ions, or molecules consisting of one type of atom are also examples of elements. But, if you are asked to name examples of elements, play it safe and list any of the elements on the periodic table rather than any isotopes, molecules, or allotropes.

  • Hydrogen (atomic number 1; element symbol H)
  • Helium (atomic number 2, element symbol He)
  • Iron (atomic number 26; element symbol Fe)
  • Neon (atomic number 10; element symbol Ne)
  • Carbon-12 and Carbon 14 (two isotopes of carbon, both with 6 protons but different numbers of neutrons)
  • Oxygen gas (O2; O3 which also has the special name of ozone)
  • Tritium (an isotope of hydrogen)
  • Diamond, graphite, and graphene (allotropes of carbon)

Note that molecules of an element can be broken into smaller pieces via chemical reactions. But, the elemental identity of the atoms remains unchanged.

Examples of Substances That Are Not Elements

If a substance contains more than one type of atom, it’s not an element. Fictional elements aren’t real chemical elements. Examples of substances that aren’t elements include:

  • Water (H2O, composed of hydrogen and oxygen atoms)
  • Steel (composed of iron, nickel, and other elements)
  • Brass (composed of copper, zinc, and sometimes other elements)
  • Air (consists of nitrogen, oxygen, and other elements)
  • Electrons
  • Neutrons
  • Plastic
  • Window
  • Cat
  • Kryptonite
  • Divinium
  • Unobtainium

Element Names, Symbols, and Atomic Numbers

There are three ways to refer to individual elements. Each element has a name, an element symbol, and an atomic number. The International Union of Pure and Applied Chemistry (IUPAC) approves standard names and symbols, but within an individual country, other element names might be used.

Some element names are historical, but most were named by the person or group who discovered them. Element names usually reference a person (real or mythical), place (real or mythical), or mineral. Many element names end with the -ium suffix, but halogen names have the -ine ending and noble gases have the -on ending. An element name refers to a single atom or ion of that element, its isotopes, or to a molecule consisting only of that element. For example, oxygen may refer to a single oxygen atom, oxygen gas (O2 or O3), or the isotope oxygen-18.

Each element also has a unique one- or two- letter symbol. Examples of symbols include H for hydrogen, Ca for calcium, and Og for oganesson.

The periodic table lists the elements in order of increasing atomic number. The atomic number is the number of protons in any atom of that element. Examples of atomic numbers include 1 for hydrogen, 2 for helium, and 6 for carbon.

Elements, Molecules, and Compounds

An element consists of only one type of atom. A molecule is composed of two or more atoms joined together by chemical bonds. Some molecules are examples of elements, such as H2, N2, and O3. A compound is a type of molecule consisting of two or more different atoms joined by chemical bonds. All compounds are molecules, but not all molecules are compounds.

Note: The IUPAC makes no distinction between molecules and compounds, defining them as a pure substance formed by a fixed ratio of two or more atoms sharing chemical bonds. By this definition, O2 would be an element, a molecule, and a compound. Because of differing definitions, chemistry teachers probably ought to stay away from questions about elements/compounds and simply focus on the 118 elements of the periodic table as examples of elements.


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  • IUPAC (1997). “Chemical Element”. Compendium of Chemical Terminology (2nd ed.) (the “Gold Book”). Blackwell Scientific Publications. doi:10.1351/goldbook
  • Myers, Rollie J. (2012). “What Are Elements and Compounds?”. J. Chem. Educ. 89 (7): 832–833. doi:10.1021/ed200269e