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 also 15.4.4, Nomenclature, Drugs, Chemical Names; and 15.9, Nomenclature, 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. For example:
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, XTC), 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, ecstasy, or XTC 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 officinalis. [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.
Repeated serum chemistry studies confirmed a serum sodium level of 140 mEq/L and a serum potassium level of 145 mEg/L.
In the text and elsewhere, the expansion of such symbols as Na+or Ca2+ can be cumbersome, since these symbols have a specific meaning for the reader. Usage should follow the context. For example, in nontechnical pieces, the flavor of the writing might be lost if, for example, 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 the printer, especially when chemical bonds are expressed. (See also 21.1, Mathematical Composition, Copy Marking.) Three types of chemical bonds commonly seen in organic and biochemical compounds are single, double, and triple:
H3–CH3 H2C=CH2 HC=CH
When deciding whether to expand or abbreviate element and chemical names, the editor and the author should consider guidelines for established terminology, the manuscript’s subject matter, technical level, and audience, and the context in which the term appears.