Editing Chemical formula (section)

=== Condensed formula ===
{{Main|Condensed formula}}
The [[connectivity (graph theory)|connectivity]] of a molecule often has a strong influence on its physical and chemical properties and behavior. Two molecules composed of the same numbers of the same types of atoms (i.e. a pair of [[isomer]]s) might have completely different chemical and/or physical properties if the atoms are connected differently or in different positions. In such cases, a [[structural formula]] is useful, as it illustrates which atoms are bonded to which other ones. From the connectivity, it is often possible to deduce the approximate [[molecular geometry|shape of the molecule]].

A condensed (or semi-structural) formula may represent the types and spatial arrangement of [[Chemical bond|bonds]] in a simple chemical substance, though it does not necessarily specify [[isomer]]s or complex structures. For example, [[ethane]] consists of two carbon atoms single-bonded to each other, with each carbon atom having three hydrogen atoms bonded to it. Its chemical formula can be rendered as {{chem2|CH3CH3}}. In [[ethylene]] there is a double bond between the carbon atoms (and thus each carbon only has two hydrogens), therefore the chemical formula may be written: {{chem2|CH2CH2}}, and the fact that there is a double bond between the carbons is implicit because carbon has a valence of four. However, a more explicit method is to write {{chem2|H2C\dCH2}} or less commonly {{chem2|H2C::CH2}}. The two lines (or two pairs of dots) indicate that a [[double bond]] connects the atoms on either side of them.

A [[triple bond]] may be expressed with three lines ({{chem2|HC\tCH}}) or three pairs of dots ({{chem2|HC:::CH}}), and if there may be ambiguity, a single line or pair of dots may be used to indicate a single bond.

Molecules with multiple [[functional group]]s that are the same may be expressed by enclosing the repeated group in [[parenthesis|round brackets]]. For example, [[isobutane]] may be written {{chem2|(CH3)3CH}}. This condensed structural formula implies a different connectivity from other molecules that can be formed using the same atoms in the same proportions ([[isomer]]s). The formula {{chem2|(CH3)3CH}} implies a central carbon atom connected to one hydrogen atom and three [[methyl group]]s ({{chem2|CH3}}). The same number of atoms of each element (10 hydrogens and 4 carbons, or {{chem2|C4H10}}) may be used to make a straight chain molecule, ''n''-[[butane]]: {{chem2|CH3CH2CH2CH3}}.