chemical formula

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Different formulas of the benzene molecule.

A chemical formula describes the composition of chemical compounds and can contain information about their structure. A chemical formula always contains information on the chemical elements contained in a compound and the numerical ratio of the particles occurring in the compound. Chemical formulas are also used to represent chemical reactions in reaction equations.

The element symbols must be distinguished from the formulas : H for hydrogen , Mg for magnesium , N for nitrogen . If two or more atoms of the same element combine to form a molecule , this is in turn characterized by a formula: H 2 for hydrogen, N 2 for nitrogen, O 3 for ozone .

Known formulas

There are different ways of writing chemical formulas. The best known are among others:

  • Molecular formula : The molecular formula indicates the number of atoms of the chemical elements that are contained in a compound . In the case of molecules , this also indicates the actual frequency of the atoms of different elements in the molecule. The empirical formulas of salts generally correspond to their ratio formulas , but are usually given in the form of formula units which satisfy the stoichiometry of the compound.
    Example: The molecular formula for benzene is C 6 H 6 , the molecular formula (formula unit) for aluminum sulfate is Al 2 (SO 4 ) 3 .

The use of the names of the individual formula types is not always standardized and many names are used synonymously. Structural formulas are mainly used to describe molecules . However, a structural formula is also used to describe ions in crystals , since the ions in the ion crystals are also "structured". A formula used for salt- like substances should be referred to as a formula unit , not a structural formula or empirical formula . The actual structure of a salt-like compound is only clarified by its crystal structure .

Comparison of different formulas with different degrees of abstraction

Structural formulas Other modes of representation
Electron formula Valence stroke formula Wedge formula Skeletal formula Constitutional formula Molecular formula Ratio formula
methane Methane electron formula Methane Lewis.svg Methane structure does not exist CH 4 CH 4 CH 4
propane Propane electron formula Propane Lewis.svg Propane structure Propane skeletal formula CH 3 -CH 2 -CH 3 C 3 H 8 C 3 H 8
acetic acid Acetic acid electron formula Acetic acid valence line formula Acetic acid structure Acetic acid skeletal formula CH 3 -COOH C 2 H 4 O 2 CH 2 O
water Water electron formula.svg WasserValenz.svg WasserKonstitution.svg does not exist H 2 O H 2 O H 2 O

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