All style advice in this document is consistent with the ACS Guide to Scholarly Communication ¹. Consult this resource if you are ever uncertain about grammar, punctuation, formatting, and other style issues. By following the style and norms of technical writing, your scientific peers will take your writing seriously and absorb your results and ideas effortlessly.

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", "the instructor", or other details about the course. It is redundant to refer to your work as an experiment. Details about the course or which student did what work are irrelevant to the scientific phenomena under study (unless course design is the subject of the experiment).

Do not use lab slang in manuscripts or reports. Some common examples follow.

• "Mass" is not recognized as a verb that means "to measure the mass of".² This verb refers to gathering things into a mass (e.g. "the soldiers massed at the border"). A mass balance weighs a substance, regardless of whether it gives units of mass or force. Substituting "massed" for "weighed" is unprofessional lab slang. Moreover, it is unecessarily redundant to say, "the mass was measured and found to be 25.01 g." Simply state that "25.01 g" was used in the experiment. Your reader understands that you measured something if you state the result.
• "Rotovap" is also not a recognized verb outside of slang. Instead, state that "solvent was removed under reduced pressure."
• A scientific instrument is generally not a "machine" in technical writing. This word should only be used for devices that do work with mechanical energy. For example, instead of "NMR machine" or "mass spectroscopy machine", refer to the instrument as an "NMR spectrometer" or a "mass spectrometer" respectively.

Do not use the possessive apostrophy for non-human subjects in an experiment. This style is currently considered unprofessional in a research report. For example, rather than refer to "the sample's color", instead say "the color of the sample".

Numerical presentation

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

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)

• Spell-out cardinal numbers less than 10 when used in a nontechnical sense (e.g. for counted items); use numerals in a technical or nontechnical sense for 10 and above (e.g. three flasks).
  • Example: Never spell measured values. Thus, you should write "2 grams" not "two grams" or "a pH of 7.0" not "a pH of seven."
• Spell out ordinals “first” through “ninth”; use numerals for 10th or greater. Never superscript the ordinal abbreviation.
• Use numerals with units of time or measure (e.g. 25 mL, 6 min, 50%, 12:15 a.m.).
• When numerals are used as names and not enumerators, form their plurals by adding an apostrophe and “s” to avoid confusion with mathematical expressions and to make it clear that the “s” is not part of the name. (e.g. The athlete received five 9’s from the judges.)

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.

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

Scientific notation: For very large and very small numbers with units of measure, use scientific notation or choose an appropriate multiplying prefix for the unit to avoid presenting numbers of more than four digits.

• Example: 5.8 × 10⁻⁵ M or 58 μM
• The multiplication symbol (×) is not the same as the letter x. In Word, type \times with Math Autocorrect activated to easily access this symbol.

Punctuation and Grammar

Capitalization:  At the start of a sentence, do not capitalize hyphenated lowercase descriptors, but do capitalize the first word (e.g. "trans-Stilbene was reacted..." or "α-Helices form...").  Do not start a sentence with an abbreviation that itself starts with a lowercase letter (e.g. "pH" or "mRNA"); instead rephrase the sentence.

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.

Quantities of: 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."

Quotation marks and punctuation: In technical writing, follow the rule of logical placement instead of traditional practices. Thus, if the punctuation is part of the quotation, then it should be within the quotation marks; if the punctuation is not part of the quotation, then the writer should not mislead the reader by implying that it is, and the punctuation should fall outside the closing quotation mark. Do not use quotation marks merely for emphasis. Instead, use italic type, but use it sparingly.

Spacing:

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.

• Examples: –12 °C, a conversion of >50%, 25 g (±1%), at 400× magnification (the negative, greater-than, plus-minus, and times signs are all adjectives).

Leave space around mathematical operators that function as verbs or conjunctions; that is, there is at least one number around the symbol.

• Examples: T_f = 156 °C, 3.24 ± 0.01, 4 × 10¹² (the equals sign is a verb and the plus-minus and times sugns are conjunctions).
• Exception 1: Leave no space around mathematical operators in subscripts and superscripts, e.g. ΔH^n-1, E_λ>353.
• Exception 2: Leave no space around colons and and slashes in ratios and mixtures (see Ratio an Mixture notation).

 

References

1. Banik G.M., Baysinger G., Kamat P., Pienta N.The ACS Guide to Scholarly Communication. American Chemical Society: Washington DC. DOI: https://doi.org/10.1021/acsguide.
2. "mass, verb." The Oxford English Dictionary Online. 2019. https://www-oed-com.ezproxy.depaul.edu/view/Entry/114670?result=7 (accessed 5 Sept 2019).