Appendix D: Scientific Style

All style advice in this document is consistent with the guidelines in the ACS Style Guide 2. The ebook in PDF format is available on the D2L course site and The most current version is available from the ACS website. Consult this resource if you are ever uncertain about grammar, punctuation, formatting, and other style issues

Active versus Passive Voice

A sentence is said to be in active voice when the subject of the sentence is the doer of the action indicated by the verb. The subject of an active verb is doing the action of the verb. In passive voice, the subject is the receiver of the action indicated by the verb.

Use the passive voice when the doer of the action is not important or unknown, or when you would prefer not to specify the doer of the action. In procedures, results, and discussions of concepts the particular researcher doing the action is not important to the outcome, thus these should be written in the passive voice since.

  • The solution was shaken until the precipitate formed.
  • Melting points and boiling points were approximated.

Use the active voice when it is less wordy and more direct than the passive.

Use first person only when it helps to keep your meaning clear and to express a purpose or a decision. Avoid subjusted clauses such as "we believe", "we feel", and "we can see" in technical writing. The following examples are appropriate uses personal pronouns.

  • Jones reported xyz, but I (or we) found ....
  • I (or we) present here a detailed study ....
  • Our recent work demonstrated ....
  • To determine the effects of structure on photophysics, I (or we) ....
Verb Tense

Using the appropriate verb tense helps to orient the reader as to the nature of the information.

Use simple past tense to state what was done, either by others or by you.

  • The solutions were heated to boiling.
  • Jones reviewed the literature and gathered much of this information.
  • We found that relativistic effects enhance the bond strength.
  • The structures were determined by neutron diffraction methods.
  • The absence of substitution was confirmed by preparative-scale electrolysis.

Present tense is correct and recommended for general statements of fact.

  • Absolute rate constants for a wide variety of reactions are available.
  • Hyperbranched compounds are macromolecular compounds that contain a branching point in each structural repeat unit.
  • IR spectroscopy shows that nitrates are adsorbed and are not removed by washing with distilled water.

Present and simple past tenses may both be correct for results, discussion, and conclusions, however, the use of present or simple past tense in these sections should be consistent within a paper. Be aware that changing verb tense has implications to the reader.

  • The characteristics of the voltammetric wave indicate that electron transfer occurs spontaneously. [this is a general fact]
  • The characteristics of the voltammetric wave indicated that electron transfer occured spontaneously. [this is a description of results]
Language and tone

Do not refer to "the experiment," "the lab section," "the instructor," or other details about the course. The reader will assume that an experiment is being described. Administrative details about the course are irrelevant to the science reported (unless course design is the subject of the experiment).

  • Do not use lab slang in manuscripts or reports.
    • Example: You do not "mass" a substance. A mass balance weighs a substance, regardless of whether it gives units of mass or force. "Mass" is not recognized as a verb that means "to measure the mass of."1 Furthermore, stating the action of a simple measurement in writing is generally unnecessary. The reader understands that you measured the mass if you simply state the result, e.g. "25.01 grams".
    • Example: You do not "rotovap" a solution. This is also not a recognized verb outside of slang. Instead, state that "solvent was removed under reduced pressure."
  • In technical writing, it is inappropriate to call a scientific instrument a "machine." This word should only be used for devices that do work with mechanical energy. For example, instead of "NMR machine" or "mass spectroscopy machine", name the instrument as "NMR spectrometer" or "mass spectrometer" respectively.
Punctuation and Grammar

Decimals: For decimal fractions less than unity, always give a leading zero; e.g., "0.5 mL," not ".5 mL."

Hyphens: Always hyphenate compound adjectives, such as a "10-mL portion" or a "freshly-distilled solvent."

Instruments: You measure a spectrum "with" a spectrometer, not "on" a spectrometer. This applies to all spectra, i.e. NMR, infrared, optical rotations, etc.

Italics: Italicize the genus and species of an organism (e.g. Agaricus bisporus) and use normal type for the genus only (e.g. Agaricus mushrooms).

Naming chemical compounds: If you use abbreviation numbers to refer to chemical structures, the numbers are parenthesized if the number is used as an adjective and not parenthesized if the number is a noun; e.g., "amine 5 was distilled" and "the procedure gave 56% yield of 2-methylcyclohexanone (7)." In the first example "5" is the noun and "amine" is an adjective. In the second example "2-methylcyclohexanone" is a noun and "7" is an adjective. A simple test you can apply to see if the number should be parenthesized or not is to see whether you still have a valid sentence if the number is left out; the sentence will still work if an adjective is eliminated but not if a noun is eliminated.

Numbers: With items other than units of time or measure, use words for cardinal numbers less than 10; use numerals for 10 and above. (ACS 2006, 203)

  • Exception: Never spell measured values. Thus, you should write "2 grams" not "two grams" or "a pH of 7.0" not "a pH of seven."

Numbers at the start of sentences: Do not begin sentences with numerals, formulas, or abbreviations. (ACS 2006, 204)

  • It is permitted to begin a sentence with a number if it is part of a chemical name.
    • Example: 1,3-Cyclohexadiene was the least reactive of the compounds in Table 2.
  • When a sentence starts with a specific quantity, spell out the number as well as the unit of measure.
    • Example: Fifteen milliliters of supernate was added to the reaction vessel.
  • However, if possible, recast the sentence.
    • Example: Acetone (25 mL) was added, and the mixture was centrifuged.
    • Example: A 25 mL portion of acetone was added, and the mixture was centrifuged.

Quantities: In specifying quantities in the Experimental section, do not omit "of." For example, "10 mL of buffer was added," not "10 mL buffer was added."

Ratio and mixture notation: Use a colon to represent a ratio. Use either a slash or an en dash between components of a mixture (with no spaces), but not a colon. (ACS 2006, 222)

  • Example: dissolved in 5:1 glycerin/water
  • Example: dissolved in 5:1 glycerin–water


  • There is a space between a quantity and its units.
    • Examples: –78 °C, 7 mL, 5 h, 15 min.
    • Exceptions: the percent sign (e.g. 30%), the degree sign when referring to a measured angle (e.g., α = 4.234°), and currency symbols (e.g. $1000).
  • When mathematical symbols are used as adjectives, that is, with one number that is not part of a mathematical operation, do not leave a space between the symbol and the number. (ACS 2006, 215)
    • Examples: –12 °C, a conversion of >50%, 25 g (±1%), at 400× magnification.
  • Leave space around mathematical operators, function as verbs or conjunctions; that is, there is at least one number around the symbol. (ACS 2006, 215)
    • Example: Tf = 156 °C, 3.24 ± 0.01, 4 × 1012.
    • Exception 1: Leave no space around mathematical operators in subscripts and superscripts, e.g. ΔHn-1, Eλ>353.
    • Exception 2: Leave no space around colons and and slashes in ratios and mixtures (see Ratio an Mixture notation).



  1. "mass, verb." The Oxford English Dictionary Online. 2019. (accessed 5 Sept 2019).