Empirical formula
From Wikipedia, the free encyclopedia
 |
This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2008) |
In chemistry, the empirical formula of a chemical compound is a simple expression of the relative numbers of each type of atom in it, or the simplest whole number ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic compounds, such as CaCl2, and for macromolecules, such as SiO2. The term empirical refers to the process of elemental analysis, a technique of analytical chemistry used to determine the relative amounts of each element in a chemical compound.
In contrast, the molecular formula identifies a numbers of each type of atom in a molecule, and the structural formula also shows the structure of the molecule.
For example, the chemical compound n-hexane has the structural formula CH3CH2CH2CH2CH2CH3, which shows that it has 6 carbon atoms arranged in a straight chain, and 14 hydrogen atoms. Hexane's molecular formula is C6H14, and its empirical formula is C3H7, showing a C:H ratio of 3:7.
[edit] Examples of common substances
| Substance | Molecular formula | Empirical formula |
|---|---|---|
| Water | H2O | H2O |
| Methane | CH4 | CH4 |
| Benzene | C6H6 | CH |
| Sulfur | S8 | S |
| Glucose | C6H12O6 | CH2O |
[edit] Use in physics
In physics, an empirical formula is a mathematical equation that predicts observed results, but is derived from experiment or conjecture and not directly from first principles.
An example was the Rydberg formula to predict the wavelengths of hydrogen spectral lines. Proposed in 1888, it perfectly predicted the wavelengths of the Lyman series, but lacked a theoretical basis until Niels Bohr produced his Bohr model of the atom in 1913.
Construction of empirical formulas for prediction of experimental data is considered by M.Ribaric and L.Sustersic in http://arxiv.org/pdf/0810.0905 so as to point out relevant technical problems.
[edit] See also
- Empiricism (Philosophic usage and history)
- Empirical research (More on the scientific usage)
- Empirical
- Phenomenology
