Editing Tip: Indefinite Article Use with Elements

  • Chemical elements present some unusual exceptions to normal rules for usage of indefinite articles (a and an)
  • Choose the article based on the sound of the element when sounded out fully (e.g., ‘silver’ not ‘Ag’)
  • For isotopes, consider the sound of the element symbol first
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Elsewhere, we discuss proper article usage in general and how to choose an indefinite article (a or an) for use with an abbreviation. Typically, a precedes a consonant sound, and an precedes a vowel sound (for further information, please see this editing tip). Here, guided by two common questions and building upon a post about tricky chemistry conventions, we detail indefinite article use with elements, including isotope forms:

Should the pronunciation of an element’s full name or its symbol be used to choose an indefinite article?

The American Chemical Society (ACS) style guide states that the full element name, rather than its abbreviated form, should be considered when choosing whether to use a or an. Therefore, “a Ag nanoparticle” is correct because this phrase is read as “a silver nanoparticle,” where “silver” begins with a consonant sound; pronouncing the phrase as “ay-gee nanoparticle,” which would merit the use of an due to the vowel sound “ay,” is less standard. Here are two additional examples:

  • A Li battery (“Li” is pronounced “lithium,” which begins with a consonant sound)
  • An Ar laser (“Ar” is pronounced “argon,” which begins with a vowel sound)

Should the pronunciation of an isotope’s number, full element name, or symbol be used to choose an indefinite article?

Isotopes are usually read as “element abbreviation-number” rather than “number-element abbreviation,” even if written in the latter format. Therefore, “35S” is pronounced as “ess-35,” necessitating the indefinite article an because of the vowel sound. This convention is also supported by the ACS style guide. Two more examples are listed below:

  • An 3H-labeling experiment (“3H” is pronounced “aitch-3,” which begins with a vowel sound)
  • A 14C-dating analysis (“14C” is pronounced “cee-14,” which begins with a consonant sound)

As always, if in doubt, search Google Scholar to verify which indefinite article is used most often in a particular case. For example, “a Ag nanoparticle” yields 804 hits, whereas “an Ag nanoparticle” results in approximately 40% fewer hits (515 total).

We hope that this editing tip has elucidated which indefinite articles to use before element names. Please contact us if you have any comments or questions on this topic. Best wishes from AJE!

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