Chemical formula: Difference between revisions
Jump to navigation
Jump to search
imported>John →top: fmt |
imported>Preimage |
||
| Line 1: | Line 1: | ||
{{short description|Compact notation for chemical compounds}} | {{short description|Compact notation for chemical compounds}} | ||
{{pp-vandalism|small=yes}} | {{pp-vandalism|small=yes}} | ||
{{Multiple issues| | |||
{{Sources exist|date=July 2024}} | {{Sources exist|date=July 2024}} | ||
{{More citations needed|date=January 2026}} | |||
}} | |||
{{Infobox | {{Infobox | ||
| title = <chem>Al_2(SO_4)_3</chem> | | title = <chem>Al_2(SO_4)_3</chem> | ||
| Line 69: | Line 72: | ||
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}}. | 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}}. | ||
=== Crystal-chemical formula === | |||
Chemical formulae for inorganic crystals typically omit structural information of value to crystallographers and mineralologists, such as the linkage type ([[coordination polymer|dimensionality]]) of subnetworks within the crystal, the [[polyhedral symbol|coordination polyhedron]] ([[coordination geometry]] of the [[coordination sphere|first coordination sphere]]) of each atom, and the structural connectivity between subunits.<ref name=Parthe1980>{{cite journal |last1=Parthé |first1=E. |author-link1=:d:Q15043930 |title=Crystal-chemical formulae for simple inorganic crystal structures |journal=Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry |date=15 January 1980 |volume=36 |issue=1 |pages=1–7 |doi=10.1107/S0567740880002312}}</ref> The [[International Union of Crystallography]] (IUCr) has proposed a crystal-chemical formula notation that extends standard formulae with optional annotations for these items.<ref name=IUCR1990>{{cite journal |last1=Lima-de-Faria |first1=J. |last2=Hellner |first2=E. |last3=Liebau |first3=F. |last4=Makovicky |first4=E. |last5=Parthé |first5=E. |author-link5=:d:Q15043930 |title=Nomenclature of inorganic structure types. Report of the International Union of Crystallography Commission on Crystallographic Nomenclature Subcommittee on the Nomenclature of Inorganic Structure Types |journal=[[Acta Crystallographica Section A]] |date=1 January 1990 |volume=46 |issue=1 |pages=1–11 |doi=10.1107/S0108767389008834 <!--|url=https://www.iucr.org/resources/commissions/crystallographic-nomenclature/inorganic-->}}</ref> | |||
For example, while [[quartz]], [[fibrous silica]], and [[stishovite]] all have the same [[formula unit]] {{chem2|SiO2}}, their crystal-chemical formulas demonstrate the structural differences between these [[crystal polymorphism|polymorphs]] of silica: quartz may be described as {{nowrap|{{SubSup||∞|3}}[Si<sup>[4''t'']｢1;4｣</sup>O<sub>2</sub>]}}, indicating it has a three-dimensional network structure with [[tetrahedral coordination geometry]] at each Si atom, where each {{chem2|SiO4}} tetrahedron is linked to four adjacent tetrahedra via single shared O atoms; fibrous silica may be described as {{nowrap|{{SubSup||∞|1}}[Si<sup>[4''t'']｢2;2｣</sup>O<sub>2</sub>]}}, indicating it consists of one-dimensional chains of {{chem2|SiO4}} tetrahedra, each linked to two others via shared pairs of O atoms; and stishovite may be described as {{nowrap|{{SubSup||∞|3}}[Si<sup>[6''o'']｢1,1,1,1,1,1,1,1,2,2;10｣</sup>O<sub>2</sub>]}}, indicating it has a three-dimensional network structure with [[octahedral coordination geometry]] at each silicon atom, where each {{chem2|SiO6}} octahedron is linked to ten adjacent octahedra, eight via single shared O atoms and two via shared pairs of O atoms.<ref name=IUCR1990/> | |||
=== Chemical names in answer to limitations of chemical formulae ===<!-- what why here??? --> | === Chemical names in answer to limitations of chemical formulae ===<!-- what why here??? --> | ||
| Line 120: | Line 128: | ||
The following example formulae are written using the Hill system, and listed in Hill order: | The following example formulae are written using the Hill system, and listed in Hill order: | ||
* BrClH<sub>2</sub>Si | * BrClH<sub>2</sub>Si ([[bromo(chloro)silane]]) | ||
* BrI | * BrI ([[iodine monobromide]]) | ||
* CCl<sub>4</sub> | * CCl<sub>4</sub> ([[carbon tetrachloride]]) | ||
* CH<sub>3</sub>I | * CH<sub>3</sub>I ([[iodomethane]]) | ||
* C<sub>2</sub>H<sub>5</sub>Br | * C<sub>2</sub>H<sub>5</sub>Br ([[bromoethane]]) | ||
* H<sub>2</sub>O<sub>4</sub>S | * H<sub>2</sub>O<sub>4</sub>S ([[sulfuric acid]]) | ||
== See also == | == See also == | ||