Empirical formula

This article is about analytical chemistry. For observation rather than theory, see Empirical relationship.

In chemistry, the empirical formula of a chemical compound is the simplest whole number ratio of atoms present in a compound.[1] A simple example of this concept is that the empirical formula of sulfur monoxide, or SO, is simply SO, as is the empirical formula of disulfur dioxide, S2O2. Thus, sulfur monoxide and disulfur dioxide, both compounds of sulfur and oxygen, have the same empirical formula. However, their molecular formulas, which express the number of atoms in each molecule of a chemical compound, are not the same.

An empirical formula makes no mention of the arrangement or number of atoms. It is standard for many ionic compounds, like calcium chloride (CaCl2), and for macromolecules, such as silicon dioxide (SiO2).

The molecular formula, on the other hand, shows the number of each type of atom in a molecule.[2] The structural formula shows the arrangement of the molecule. It is also possible for different types of compounds to have equal empirical formulas.

In the early days of chemistry, information regarding the composition of compounds came from elemental analysis, which gives information about the relative amounts of elements present in a compound, which can be written as percentages or mole ratios. However, chemists were not able to determine the exact amounts of these elements and were only able to know their ratios, hence the name "empirical formula". Since ionic compounds are extended networks of anions and cations, all formulas of ionic compounds are empirical.[3]

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Empirical formula". doi:10.1351/goldbook.E02063
  2. ^ MONITOR., WHOLE SKY, URL., OCLC 796720402, retrieved 2022-12-31
  3. ^ "10.12: Determining Empirical Formulas". Chemistry LibreTexts. 2016-06-27. Retrieved 2023-08-14.