Definition of Chemical Formula

Know the Types of Chemical Formulas

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Helmenstine, Anne Marie, Ph.D. "Definition of Chemical Formula." ThoughtCo, Apr. 9, 2017, thoughtco.com/definition-of-chemical-formula-604906. Helmenstine, Anne Marie, Ph.D. (2017, April 9). Definition of Chemical Formula. Retrieved from https://www.thoughtco.com/definition-of-chemical-formula-604906 Helmenstine, Anne Marie, Ph.D. "Definition of Chemical Formula." ThoughtCo. https://www.thoughtco.com/definition-of-chemical-formula-604906 (accessed October 19, 2017).
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The chemical formula for water indicates each molecule contains 2 hydrogen atoms and 1 oxygen atom. WIN-Initiative / Getty Images

A chemical formula is an expression which states the number and type of atoms present in a molecule of a substance. The type of atom is given using element symbols. The number of atoms is indicated by a subscript following the element symbol.

Chemical Formula Examples

  • There are 6 C atoms and 14 H atoms in a hexane molecule, which has a molecular formula of C6H14.
  • The chemical formula of table salt or sodium chloride is NaCl. There is one sodium atom and one chlorine atom in each molecule. Note there is no subscript for the number "1".

    Types of Chemical Formulas

    While any expression that cites the number and kind of atoms is a chemical formula, there are different types of formulas, including molecular, empirical, structure, and condensed chemical formulas.

    Molecular Formula

    Also known as the "true formula", the molecular formula states the actual number of atoms of the elements in a single molecule. For example, the molecular formula of the sugar glucose is C6H12O6.

    Empirical Formula

    The empirical formula is the simplest ratio of the whole number of elements in a compound. It gets its name because it comes from experimental or empirical data. It's sort of like simplifying mathematical fractions. Sometimes the molecular and empirical formula are the same (e.g., H2O), while other times the formulas are different. For example, the empirical formula of glucose is CH2O, which is obtained by dividing all of the subscripts by the common value (6, in this case).

    Structural Formula

    Although the molecular formula tells you how many atoms of each element are present in a compound, it does not indicate the way the atoms are arranged or bonded to each other. A structural formula shows the chemical bonds. This is important information because two molecules may have share the same number and type of atoms, yet be isomers of each other.

    For example, ethanol (grain alcohol people can drink) and dimethyl ether (a toxic compound) share the same molecular and empirical formulas.

    There are different types of structural formulas, too. Some indicate the two-dimensional structure, while others describe the three-dimensional arrangement of atoms.

    Condensed Formula

    One particular variation of an empirical or structural formula is the condensed formula. This type of chemical formula is a sort of shorthand notation, The condensed structural formula may omit the symbols for carbon and hydrogen in the structure, simply indicating the chemical bonds and formulas of functional groups. The written condensed formula lists the atoms in the order in which they appear in the molecular structure. For example, the molecular formula of hexane is C6H14, but its condensed formula is CH3(CH2)4CH3. This formula not only provides the number and type of atoms, but also indicates their position in the structure.