Editing Chemical formula (section)

{{short description|Compact notation for chemical compounds}}
{{pp-vandalism|small=yes}}
{{Sources exist|date=July 2024}}
{{Infobox
| title            = <chem>Al_2(SO_4)_3</chem>
| data2            = Chemical formula for [[aluminium sulfate]]
}}
{{Infobox
| title            = <chem>H-\overset{\displaystyle H \atop |}{\underset{| \atop \displaystyle H}{C}}-\overset{\displaystyle H \atop |}{\underset{| \atop \displaystyle H}{C}}-\overset{\displaystyle H \atop |}{\underset{| \atop \displaystyle H}{C}}-\overset{\displaystyle H \atop |}{\underset{| \atop \displaystyle H}{C}}-H</chem>
| data2            = [[Structural formula]] for [[butane]]
}}

A '''chemical formula''' is a way of  presenting information about the chemical proportions of [[atom]]s that constitute a particular [[chemical compound]] or [[molecule]], using [[chemical element]] symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and ''plus'' (+) and ''minus'' (−) signs. These are limited to a single typographic line of symbols, which may include [[Subscript and superscript|subscripts and superscripts]]. A chemical formula is not a [[chemical nomenclature|chemical name]] since it does not contain any words. Although a chemical formula may imply certain simple [[chemical structure]]s, it is not the same as a full chemical [[structural formula]]. Chemical formulae can fully specify the structure of only the simplest of molecules and [[chemical substance]]s, and are generally more limited in power than chemical names and structural formulae.

The simplest types of chemical formulae are called ''[[empirical formula]]e'', which use letters and numbers indicating the numerical ''proportions'' of atoms of each type. '''Molecular formulae''' indicate the simple numbers of each type of atom in a molecule, with no information on structure. For example, the empirical formula for [[glucose]] is {{chem2|CH2O}} (twice as many [[hydrogen]] atoms as [[carbon]] and [[oxygen]]), while its molecular formula is {{chem2|C6H12O6}} (12 hydrogen atoms, six carbon and oxygen atoms).

Sometimes a chemical formula is complicated by being written as a [[condensed formula]] (or condensed molecular formula, occasionally called a "semi-structural formula"), which conveys additional information about the particular ways in which the atoms are [[chemical bond|chemically bonded]] together, either in [[covalent bond]]s, [[ionic bond]]s, or various combinations of these types. This is possible if the relevant bonding is easy to show in one dimension. An example is the condensed molecular/chemical formula for [[ethanol]], which is {{chem2|CH3\sCH2\sOH}} or {{chem2|CH3CH2OH}}. However, even a condensed chemical formula is necessarily limited in its ability to show complex bonding relationships between atoms, especially atoms that have bonds to four or more different [[substituent]]s.

Since a chemical formula must be expressed as a single line of chemical [[element symbol]]s, it often cannot be as informative as a true structural formula, which is a graphical representation of the spatial relationship between atoms in chemical compounds (see for example the figure for butane structural and chemical formulae, at right). For reasons of structural complexity, a single condensed chemical formula (or semi-structural formula) may correspond to different molecules, known as [[isomer]]s. For example, glucose shares its [[molecular formula]] {{chem2|C6H12O6}} with a number of other [[sugar]]s, including [[fructose]], [[galactose]] and [[mannose]]. Linear equivalent chemical ''names'' exist that can and do specify uniquely any complex structural formula (see [[chemical nomenclature]]), but such names must use many terms (words), rather than the simple element symbols, numbers, and simple typographical symbols that define a chemical formula.

Chemical formulae may be used in [[chemical equation]]s to describe [[chemical reaction]]s and other chemical transformations, such as the dissolving of ionic compounds into solution. While, as noted, chemical formulae do not have the full power of structural formulae to show chemical relationships between atoms, they are sufficient to keep track of numbers of atoms and numbers of electrical charges in chemical reactions, thus [[Chemical equation#Balancing chemical equations|balancing chemical equations]] so that these equations can be used in chemical problems involving conservation of atoms, and conservation of electric charge.