A chemical formula of the composition of chemical compounds, and may contain information on the structure. A chemical formula always contains information about the chemical elements contained in a compound and the ratio of the number occurring in the compound particles.
Of the formulas, the element symbols are to be distinguished: H is hydrogen, of magnesium Mg, N for nitrogen. When two or more atoms of the same element in a molecule is then in turn characterized by a ( molecular ) formula: H2 hydrogen, nitrogen N2, O3 for ozone.
The various levels of chemical formulas:
- Ratio formula: It is composed of element symbols and small, subscripts (indices) together and gives only the ratio again, in which the individual chemical elements are present in a chemical compound. This integer ratios are used.
- Empirical formula: The empirical formula is in each case to the number of atoms of chemical elements that are contained in a compound. For molecules therefore the actual frequency of the atoms of different elements is specified in the molecule. The molecular formulas of salts corresponding to their ratio formulas in the rule, but are usually given in the form of formula units that satisfy the stoichiometry of the compound.
- Structure: The structural formula is, in addition to the number of different atoms in a molecule, their relationship to each other again, which means it also provides information about the nature of atoms and the nature of their linkages ( bonds), where appropriate, the bond angles and bond lengths. The letters stand for individual atoms. A dash represents a pair of electrons present in a cloud of electrons / orbital and either makes the bond between atoms or a so-called lone pair of electrons. Two parallel lines denote corresponding to a double bond.
- Crystal chemical structural formula: it is a special formula notation that is used in mineralogy for more complex chemical compounds. Chemical structural formula of the crystal based on the empirical formula, but the components grouped by the cations and anions as well as the structural position of the anions.
Use of the names of the different types of formula is not always standardized and many terms are used interchangeably. Structural formulas are mainly used to describe molecules. However, a structure of the formula is also used for the description of ions in crystals, as the ions in the ion crystal and "structured" is. A formula used for salt-like substances should be referred to as formula unit, not as a structural formula or molecular formula. The actual structure of a salt-like compound is cleared only by its crystal structure.
Other display options
- Constitutional formula
- Lewis formula: all bonding and non- bonding electron pairs or lone electron are shown without consideration of the bond angles and bond lengths.
- Skeletal formula, abbreviated notation in Organic Chemistry
- A wedge line formula to show the stereochemistry
- Fischer projection formula for chiral molecules such as amino acids or sugar
- Haworth projection, for 5 - to 6- ringige molecules such as sugar
- Newman projection formula to represent the conformation
- Structure codes: INCHI, SMILES, WLN