Elements and Chemicals - Abbreviations

AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020

Elements and Chemicals

In general, the names of chemical elements and compounds should be expanded in the text at first mention and elsewhere in accordance with the guidelines for clinical and technical terms (see 14.4.4, Chemical Names, and 14.9, Isotopes). However, in some circumstances, it may be helpful or necessary to provide the chemical symbols or formulas in addition to the expansion if the compound under discussion is new or relatively unknown or if no nonproprietary term exists.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD or dioxin) is often referred to as the most toxic synthetic chemical known. [Use “TCDD” or “dioxin” thereafter; TCDD is more specific because there is more than 1 form of dioxin.]

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy), a synthetic analogue of 3,4-methylenedioxyamphetamine, has been the center of controversy over its potential for abuse vs its use as a psychotherapeutic agent. [Use “MDMA” or “ecstasy” thereafter, depending on the article’s context.]

The following format may also be used:

Isorhodeose (chemical name, 6-deoxy-D-glucose [CH3(CHOH)4CHO]) is a sugar derived from cinchona bark. [Use “isorhodeose” thereafter.]

Names such as “sodium lauryl sulfate” are easier to express and understand (and typeset) than “CH3(CH2)10CH2OSO3Na.” Similarly, “oxygen” and “water” do not take up much more space than “O2” and “H2O” and hence should remain expanded throughout a manuscript, unless specific measurements (eg, gas exchange) are under discussion.

The venous CO2 pressure is always greater than arterial CO2 pressure; specifically, PvCO2/PaCO2 is greater than 1.0 except when PO2 plus PCO2 is measured. Nevertheless, the CO2 levels should be carefully measured.

Near the earth’s surface, the atmosphere has a well-defined chemical composition, consisting of molecular nitrogen, molecular oxygen, and argon. It also contains small amounts of carbon dioxide and water vapor, along with trace quantities of methane, ammonia, nitrous oxide, hydrogen sulfide, helium, neon, krypton, xenon, and various other gases.

In the following example, sodium and potassium are not abbreviated.

Additional serum chemistry studies confirmed a serum sodium level of 131 mEq/L and a serum potassium level of 4.8 mEq/L.

In the text and elsewhere, the expansion of such symbols as Na+ or Ca2+ can be cumbersome because these symbols have a specific meaning for the reader. Usage should follow the context. For example, in narrative or nontechnical pieces, the flavor of the writing might be lost if the editor arbitrarily changed “CO2” to “carbon dioxide” (“What’s the patient’s CO2?”).

When chemical symbols and formulas are used, they must be carefully marked for display and typesetting, especially when chemical bonds are expressed (see 20.0, Mathematical Composition). Three types of chemical bonds commonly seen in organic and biochemical compounds are single, double, and triple:

H3 — CH3

H2C = CH2


mark single bond

mark double bond

mark triple bond

When deciding whether to expand or abbreviate element and chemical names, the editor and the author should consider guidelines for established terms; the manuscript’s subject matter, technical level, and audience; and the context in which the term appears.