This guideline is a part of the English Wikipedia's Manual of Style.
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This page aims to be brief, touching on the general aspects of chemistry-related articles. In-depth guides are found in linked pages.
Many chemical topics are suitable for inclusion; the central criterion is that the article meets the general notability guidelines. Important topics include compounds, reactions, methods of analysis, instrumentation/apparatus, techniques, significant chemists, branches of chemistry, chemical theories, and principles which have received significant coverage in independent reliable sources.
The style of editing embraced by the Wikipedia chemistry project is collaborative and consensus-driven. Edits to existing articles are typically incremental, which allow changes to be evaluated by other editors. Long-standing or mature articles should not be rewritten in their entirety because such large-scale changes inhibit discussion and often marginalize seemingly small but significant improvements that have been hammered out by previous editors. If an editor feels that a mature article warrants a major revision, it is both customary and considerate for the revising editor to announce their intentions on the relevant talk page and to heed the consensus of the responses. Typically, responses to such announcements can take days to accumulate, so major revisions require a sense of pace and patience.
Being affiliated with or bound by no scientific organizations, the content in Wikipedia-Chemistry is not constrained by recommendations or rules, but seeks to objectively describe knowledge. For example, the International Union of Pure and Applied Chemistry (IUPAC) provides recommendations and definitions for nomenclature and terminology. Wikipedia editors strive to be mindful of IUPAC's advice but do not follow this advice rigidly, especially when the advice deviates from mainstream usage (see comments below on nomenclature).
The thousands of Wikipedia articles about chemistry benefit from continuing improvements that address clarity and content. Very long articles are difficult to read and maintain, so at some stage, long articles are often split (subdivided into two articles). Being a consensus driven process, plans for splitting are ordinarily discussed on the talk page for the parent article.
Articles are placed in one or more categories to help readers and editors locate similar topics. When categories become too large to be readily searched, it is common to create subcategories. For example, Category:Alcohols has subcategories Category:Tertiary alcohols, Category:Secondary alcohols, and Category:Primary alcohols. Prior to creating multiple categories, such plans are ordinarily discussed on the talk page for the parent article since they affect many articles.
In general, descriptions of chemical knowledge do not mention who did the work or where the discoveries were made, in part because such information is available in the citations. This approach simplifies the presentation and helps readers focus on facts and explanations. The obvious exceptions to this guideline are articles or sections of articles on biographies and history. Even in regular articles, scientific advances are sometimes attributed to noteworthy individuals and institutions, especially when this information illuminates the content or enlivens the prose. Attribution to individuals and institutions is subject to guidelines on conflict of interest.
Per WP:ENGVAR, the type of English used to write an article does not matter, but it should be consistent. The following exceptions apply for chemical names, when the article itself is primarily about chemistry:
Systematic nomenclature, while being precise, can be cumbersome. Commonly accepted trivial or alternative names are preferred over systematic names. In particular, IUPAC recommends the use of non-systematic names for some organic compounds, and these recommendations should be followed in article titles. Examples include acetic acid over ethanoic acid, toluene over methylbenzene, lysine over 2,6-diaminohexanoic acid.
Stock nomenclature (e.g. iron(III) chloride): there should be no space between the words and the oxidation state in parentheses (between "iron" and (III)). The oxidation numbers are stated only for cations, not for anions. Where the oxidation number is obvious (i.e. group 1 or group 2 metals), it is not included. Compounds with a substantial degree of covalency do not use Stock nomenclature.
Isotopes should be labelled by their mass number, e.g. 14C and 18F. Deuterium (2H) and tritium (3H) may be labelled "D" (or "2D") and "T" (or "3T"), respectively. Deuterated solvents for NMR use are customarily described variously as: methanol-d4 for CD3OD, DMSO-d6 for CD3SOCD3, etc. These established systems are all acceptable, but should remain consistent within an article.
For organic radicals denoted by "R", indices used for numbering must be superscript: R1−CH2−R2 (not R1−CH2−R2).
Chemical symbols shall be Roman (CaCO3) and may not be italicized by any means, neither wiki syntax nor <math> tag. Notation of atomic shells, subshells and orbitals (1s, 2p, 3d, ...) also shall be Roman. Numerals (1, 2, 3, ...) shall invariably be Roman.
In prose, carbon–carbon bond uses an en dash (–), as is normal for such compound terms. However, for skeletal formulas, the mathematical symbols minus, equals, and identity are used to represent the bonds:
This style is selected because in most professional fonts only the minus sign ⟨−⟩ matches the double bond ⟨=⟩ and triple bond ⟨≡⟩ in width, so an en dash would look out of place in a skeletal formula.
Many chemical terms have interesting etymology that merits description. Since focus of the articles and the readership is on technical aspects, sections on etymology are ordinarily placed near the end of the article.
Appropriate formats are PNG and SVG. ACS settings have been adopted as the convention. Images should be legible at 450 pixels wide, to avoid interference from the chembox on the right.
Hydrogens should be implied (hidden), except for the benefit of the target audience. The use of Me to denote methyl may be confusing. The use of Et, Pr, etc., is discouraged. When Ph is used to denote phenyl and X for halogen or any atom, it should be clearly defined within the image.
See also: § Reactions
Images of chemical compounds or their solutions are useful to readers. Most useful are colored compounds but even colorless/white samples/solutions can be useful. The provenance of these images is however impossible to verify. The following images provide some guidance.
Main page: Wikipedia:Manual of Style/Chemistry/Safety
The majority of compounds are described by a long list of potential hazards as well as H- and P-phrases. Wikipedia does not aspire to be an MSDS. The hazards associated with a chemical compound should ordinarily be described in the Chembox (via GHSPictograms, GHSSignalWord, NFPA, or MainHazard parameters; further elaborated in H- and P-phrases). The information in the Chembox is sufficient for most compounds. News reports of routine accidents, even though they may be tragic, are usually not relevant.
Three main points:
Descriptions of hazards should, as far as possible, be based on published, peer-reviewed sources (which should, of course, be cited at the appropriate point in the article). A list of resources for chemical safety information is given in the external links section of these guidelines.
In general a safety section should only be used when it adds something to an article, and should be based (where at all possible) on peer-reviewed or otherwise highly reliable sources.
See also: § Current events
Depending on the extent and nature of the information, toxicological content may be incorporated into the Safety section or it may be separate. If the compound is a drug, follow Wikipedia:WikiProject Drugs' recommendations.
Journalism. Wikipedia should not offer first-hand news reports on breaking stories. Wikipedia is not a primary source. However, our sister project Wikinews does exactly that, and is intended to be a primary source. Wikipedia does have many encyclopedia articles on topics of historical significance that are currently in the news, and can be updated with recently verified information.
Accidents and incidents occur all the time. While their scale and magnitude may merit inclusion in Wikipedia on grounds of notability, that such an accident has occurred is not sufficient justification for inclusion in the context of an article about chemicals. Wikipedia does not attempt to dispense advise on what to do in the event of a (...) incident, either. (See WP:NOTGUIDE) Historic accidents and incidents may only be contextualized in the discussion on the specific hazards of certain chemicals, without serving as case studies in itself. To reiterate, if such accidents are sufficiently notable, they should have their own article (e.g. discussion in Bhopal disaster, not in methyl isocyanate).
Further information: Wikipedia:Manual of Style/Chemistry/References and external links
Claims and statements in articles should mainly be supported by references to textbooks, monographs, and related book series. In many cases, especially for historic purposes, the primary literature (journals) are used. Intermediate between journal articles, which are often highly specialized, and books, which are not always available, are review series (e.g. Chemical Reviews, Advances in Enzymology, etc.). Patents, which are considered self-published and primary sources for Wikipedia's purposes, are sometimes cited, especially for historic purposes, but they are less useful because they are not vetted on scholarly basis, they are sometimes not very readable, and often they are not very available.
All articles on chemicals, real or hypothetical, should have a Chembox. Formulae should be readily available, variables like n, x, or y are permissible for substances of variable composition such as polymers. For compounds of defined composition, the molar masses should be available as well. The article should cover these aspects as appropriate:
Ordinarily, compounds that differ in terms of their solvent of crystallization or hydration are described in a single article. The discussion that led to this consensus is here. For example, several different hydrates are known for copper(II) sulfate as well as the anhydrous form. All of these compounds are discussed in a single article, copper(II) sulfate.
These articles belong to one of these categories:
Where a compound class does not have sufficient detail to merit a full article, it should be merged to the parent article (usually that of the acid). Articles named after a parent compound should generally appear at the plural of the parent compound.
Aspects to be covered include:
Simple chemical reactions can be typed out in text. Reactions should be indented using a colon (:), and not centered. Separate the number of molecules from the molecule symbol by a space (i.e. 3 H2 instead of 3H2). For example:
Reactions in the form of images should also be indented using a colon:
Although many organometallic reagents have complex structures involving solvation or clusters, these reagents are ordinarily depicted in simplified structures (RMgX with two-coordinate Mg, BuLi with one-coordinate Li, etc.). To facilitate sharing of drawings between different language wikis, reagents above and below arrows should consist of formulas, not words. Experimental conditions are ordinarily omitted from equations. The prose can comment on conditions, yields, and other details. Equations are ordinarily not numbered.
Do not include phase definitions unless they are absolutely essential (an example is given below). Modern textbooks and journals do not use them, so Wikipedia should not pioneer a new way of describing chemical reactions. They confuse readers trying to understand basics, since stoichiometry is conflated with phase information.
Avoid the use of
<math chem> markup notations: the plain-text character set is adequate for most chemical equations; the change in size and font form is jarring to the reader. The
<ce> tag is a deprecated synonym for
<chem>; see Help:Displaying a formula#Chemistry. Ionic equations are preferred to the molecular form. State symbols are omitted unless they are relevant (e.g. thermochemistry, to illustrate precipitation for chemical separation). "Heat" should not be a reaction product; stating ΔrH, or giving its sign is preferable (note that the use of phase information is essential for evaluating the thermodynamics):
A comma, period or other punctuation is not required at the end of a line equation.
Compounds and atoms in reactions should not be wikilinked. These links should be in the surrounding text.
Each reaction article should include the following sections:
(Taken from the Horner–Wadsworth–Emmons reaction, which is a good example of a quality organic reaction article.)