Editing Formula (section)

==Chemical formulas==
{{main|Chemical formula}}

In [[Chemistry#Modern principles|modern chemistry]], a [[chemical formula]] is a way of expressing information about the proportions of [[atom]]s that constitute a particular [[chemical compound]], using a single line of chemical [[chemical symbols|element symbols]], [[numbers]], and sometimes other symbols, such as parentheses, brackets, and plus (+) and minus (−) signs.<ref>Atkins, P.W., Overton, T., Rourke, J., Weller, M. and Armstrong, F. ''Shriver and Atkins inorganic chemistry'' (4th edition) 2006 ([[Oxford University Press]]) {{isbn|0-19-926463-5}}</ref> For example, H<sub>2</sub>O is the chemical formula for [[water]], specifying that each [[molecule]] consists of two [[hydrogen]] (H) atoms and one [[oxygen]] (O) atom. Similarly, O{{sup sub|−|3}} denotes an [[ozone]] molecule consisting of three oxygen atoms<ref>{{Cite web|url=http://www.chm.bris.ac.uk/motm/ozone/CHEM.htm|title=Ozone Chemistry|website=www.chm.bris.ac.uk|access-date=2019-11-26}}</ref> and a net [[negative charge]].

{{Image frame|width=300|content=<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>|caption=The '''[[structural formula]]''' for [[butane]]. There are three common non-pictorial types of chemical formulas for this molecule:{{unordered list
 | the '''empirical formula''' C<sub>2</sub>H<sub>5</sub>
 | the '''molecular formula''' C<sub>4</sub>H<sub>10</sub> and
 | the '''condensed formula''' (or ''semi-structural formula'') CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>.}}
|alt=A diagram showing one line of four connected Cs (carbon atoms) branching out to ten Hs (hydrogen atoms)}}

A [[chemical formula]] identifies each constituent [[chemical element|element]] by its [[chemical symbol]], and indicates the proportionate number of atoms of each element.

In [[empirical formula]]s, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound—as ratios to the key element. For molecular compounds, these ratio numbers can always be expressed as whole numbers. For example, the empirical formula of [[ethanol]] may be written C<sub>2</sub>H<sub>6</sub>O,<ref>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/702|title=Ethanol|last=PubChem|website=pubchem.ncbi.nlm.nih.gov|language=en|access-date=2019-11-26}}</ref> because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of ionic compounds, however, cannot be written as empirical formulas which contains only the whole numbers. An example is [[boron carbide]], whose formula of CB<sub>n</sub> is a variable non-whole number ratio, with n ranging from over 4 to more than 6.5.

When the chemical compound of the formula consists of simple [[molecule]]s, chemical formulas often employ ways to suggest the structure of the molecule. There are several types of these formulas, including [[molecular formula]]s and [[condensed formula]]s. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the molecular formula for [[glucose]] is C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> rather than the glucose empirical formula, which is CH<sub>2</sub>O. Except for the very simple substances, molecular chemical formulas generally lack needed structural information, and might even be ambiguous in occasions.

A [[structural formula]] is a drawing that shows the location of each atom, and which atoms it binds to.