Wikipedia:Manual of Style/Chemistry

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Manual of Style for chemistry articles

This document aims to be brief, touching on the general aspects of chemistry-related articles. In-depth guides are found in the relevant sub-pages.


Many chemical topics are suitable for inclusion, the central criterion is that the article meet the general notability guidelines. Important topics include compounds, reactions, methods of analysis, instrumentation/apparatus, techniques, significant chemists, branches of chemistry, chemical theories, and principles.

Editing policy[edit]

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. Often 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).

Article curation and creation[edit]

The thousands of articles in the Project 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.

Category creation[edit]

Articles are classified according to one or more categories that help readers and editors locate related 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.

Attributions to people and places[edit]

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 the articles does not matter, but it should be consistent. The following exceptions apply for chemical names, when the article itself is primarily about chemistry:

  • "sulfur" (and related "sulfuric", etc.), "caesium", and "aluminium" should be spelled this way regardless of the English variation used in the article, being the IUPAC names for these elements;
  • "phosphine" is preferred over "phosphane", being predominantly used in the chemical literature.

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.[1] 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 and tritium may be labelled "D", "2D", or "2H" and so on. Deuterated solvents for NMR use are customarily described variously as: CD3OD, methanol-d4; CD3SOCD3, DMSO-d6. 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.

Skeletal formulas[edit]

In prose, carbon–carbon bond uses an en dash (&ndash;), as is normal for such compound terms. However, skeletal formulas, use the mathematical symbols minus, equals, and identity to represent the bonds:

Single bond: C−C (C&minus;C)
Double bond: C=C (equal sign)
Triple bond: C≡C (C&equiv;C)

This style is selected because in most professional fonts only the minus sign matches the double bond = and triple bond in length, 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.

Structure drawing[edit]

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.


The majority of compounds are described by a long list of potential hazards as well as R&S phrases. Even innocuous chemicals such as sodium chloride have risk and safety phrases: R36, S26, S36 in their MSDSs. Wikipedia does not aspire to be an MSDS. The hazards associated with a chemical compound should ordinarily be described in the Chembox (via EUClass, NFPA, or MainHazard parameters; further elaborated in R and S 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 rules:

  • If the hazards are relatively obvious (e.g. hexafluorophosphoric acid is a strong acid, and should not be stored with bases and reactive metals) do not create a separate sub-section here.
  • The description of hazards should avoid speculation. This recommendation is partly an extension of Wikipedia NPOV policy, but not entirely. There is no need to include a section which merely states "all chemical compounds should be treated with the utmost precaution": such a section tells the reader nothing. If hazards are unknown, there is nothing for Wikipedia to say.
  • The description of hazards should avoid hyperbole. The role of Wikipedia is to give balanced and accurate information, to allow its readers to reach their own conclusions.

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.


Depending on the extent and nature of the information, toxicological content may be incorporated into the Safety section or it may be a separate. If the compound is a drug, follow Wikipedia:WikiProject Drugs' recommendations.

Current events[edit]


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).

References and external links[edit]

See /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.

Article types[edit]


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:


  • Introductory paragraph (WP:lede)
  • Properties (optional), the physical appearance of the material (at STP) Often this content is included in the lede.
  • Occurrence. Usually occurrence refers natural products, compounds or ions that exist naturally.
  • Preparation. It is our tradition to cite the first preparation of a compound. For commercially important compounds, it is often useful to distinguish reactions used in industrial production separately from "laboratory routes." For natural products, the biosynthesis is described.
  • Uses. Although compounds can be used for diverse and weird ways, this section emphasizes, hierarchically, substantial commercial applications and laboratory uses.
  • Reactions. All chemical compounds undergo many reactions, so these reactions are expected to have applicability.
  • History. Often this section would be superfluous to mention of the first preparation, but some compounds, e.g., Teflon, have rich history.
  • Safety
  • Toxicology. Often this section is blended with safety. Ideally, the LD50 would be mentioned.
  • Suppliers should not be listed unless the compound is rare and only available from one or two suppliers
  • References


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.

Compound classes[edit]

These articles belong to one of these categories:

  • monoatomic ions (chloride, bromide; oxide, sulfide)
  • polyatomic ions (nitrates, perchlorates, triflates, tetrafluoroborates)
  • functional groups (alcohols, aldehydes, acids, nitriles)
  • "backbone" moieties, both organic and inorganic
  • classes of organic compounds (including many biochemicals): steroids, aldohexoses, terpenes
  • classes of inorganic and coordination compounds: metal oxo compounds, metal carbonyl compounds, metal clusters
  • elements are handled under a separate Wikiproject with guidelines, see Wikipedia:WikiProject Elements/Guidelines

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 discussing compound classes should be clearly distinguished from the compound for which the class is named. An example is quinoline versus quinoline (compound class).

Aspects to be covered include:

  • Nomenclature
  • Structure and bonding, including illustrative bond distance and angles.
  • Properties
  • Characterization, discussing spectroscopic tools and illustrative data
  • Applications, in order of the scale or impact of the application
  • Occurrence, usually involving natural occurrence as in nature or the mineral kingdom
  • Preparation, ordinarily distinguishing between technical methods and those used in the laboratory
  • Reactions, if extensive, these entries should be aggregated thematically
  • History
  • Safety


Simple 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:

2 Na + 2 H2O → 2 NaOH + H2

Reactions in the form of images should also be indented using a colon:

An example of a Grignard reaction

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 any conditions or other relevant details.

Line equations[edit]

Avoid the use of <math> notation: the existing character set is adequate to enter reaction data; the change in size and font form is jarring to the reader. Ionic equations are preferred. 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 ΔHr, or giving its sign is preferable:

C2H5OH (g) + 3 O2 (g) → 2 CO2 (g) + 3 H2O (l) (ΔHr = −1409 kJ/mol)

instead of:

C2H5OH + 3 O2 → 2 CO2 + 3 H2O + heat

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:

  • A brief overview
This section should include a broad description of the reaction in both text and reaction scheme. References to review articles are preferred. References to the discovery of the reaction is also welcome.
  • Reaction mechanism
Reaction mechanisms often include mention of stereochemistry, order of reaction, and, for inorganics, electron count and configuration. Arrow pushing is helpful in organic chemistry.
  • Scope (optional)
Side reactions and exceptions might be included. If the outcome of the reaction is affected by small changes, such descriptions should go in this section.
  • See also (optional)
In this section, not related reactions that are not mentioned in the above text.
  • References
This entire section should only be the following text:

Additional notes:

  • Avoid language in schemes, which makes the images more versatile. Descriptions belong in the caption, which are readily edited.
  • Reaction schemes are best aligned left without borders as follows:
[[Image:Horner-Wadsworth-Emmons_Reaction_Example.png|350px|The Horner-Wadsworth-Emmons reaction]]

Result being:

The Horner-Wadsworth-Emmons reaction

(Taken from the Horner-Wadsworth-Emmons reaction, which is a good example of a quality organic reaction article.)

Other issues[edit]

The following sections are excluded from the March 2009 ratification of this style guide.

Nuclear chemistry[edit]

Nuclear reactions should follow the convention as regular chemical reactions, but the isotope and element number should be specified using {{Nuclide}}. {{SubatomicParticle}} and {{PhysicsParticle}} can be used to write the symbols for subatomic particles. For example, the beta decay of carbon-14 should be written as:

+ e + ν

Laboratory/industrial apparatus and equipment[edit]

A description of the function and the design of the piece. References tend to come in the form of product brochures and catalogs. Niche items should be mentioned in the next larger set.

Analytical techniques[edit]

Principles underpinning various techniques should be described. For example, atomic absorption spectroscopy should describe spectral lines; NMR spectroscopy should describe how nuclear spin couple to magnetic fields. Simple calculations may be used to illustrate certain concepts; detailed calculations should be omitted.

Analytical data[edit]

Compilations of analytical data are not widely useful and can detract from the readability of articles. Thus, it would be inappropriate to include lists of IR bands, NMR chemical shifts, data from powder patterns, etc. Illustrative spectroscopic data should be included when the intention is "to inform rather than to instruct," per WP:NOTTEXTBOOK.


  • Nobel Prize winners
  • People who have a reaction named after them
  • etc. etc.

See notability for people

Safety sections[edit]

The general principle is that safety sections should only be used when they add something to an article, and should be based (where at all possible) on peer-reviewed or otherwise highly reliable sources.