Empirical formula

In Chemistry, an empirical formula is a concise presentation which informs about nature and the number of the Atome S which compose a Molécule. It does not inform on the provision of the atoms which constitute it. Thus an empirical formula can correspond to several different molecules. One speaks about Isomère S when two molecules present the same empirical formula. To identify a molecule, it is necessary to know, in addition to the empirical formula, the semi-developed formulas or developed .

The nature of the atoms is indicated using the chemical symbols of the atoms which constitute the molecule considered (see periodic Tableau of the elements). One specifies, in index of each symbol, the number of each one of these atoms. The order recommended is the alphabetical order of the symbols to an exception: the carbon and the hydrogen of organic materials are always quoted in first and in this order then followed other atom alphabetically.

The empirical formulas are used in the chemical equations to describe the chemical reactions.

Examples

For example the Propane which comprises only 3 atoms of Carbone (noted C) and 8 atoms of Hydrogène (noted H) will have the following empirical formula:

Other examples of empirical formulas of:

the Water:
the Methane:
the ethylene:

the ethanol: (the correct empirical formula being)

the Butane or its isomer the Isobutane:

References

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