The format for citing an entry in a dictionary or encyclopedia is similar to citing a book chapter.
Continuously updated online versions: Publishers may create online versions which are continuously updated. When citing, the date when it was last updated or first published online should be used rather than the copyright year.
Editors: Include the names of all the editors. Separate each name with a comma followed by 'Ed.;' or 'Eds.;' e.g. Marzabadi, C. H., Webster, G., Eds.;
Volume or part number: When citing a dictionary or encyclopedia with multiple volumes or parts, include the volume or part number in the citation.
Pagination: Provide pagination information if provided. Page information may not always be available for online works, so it can be omitted.
No author: For a dictionary/encyclopaedia entry when there is no author, place the title of the entry in the author position.
Refer to Book Sets Table 4.3.18 and Continuously Updated Books and Book Series Table 4.3.19 of the ACS Guide to Scholarly Communication for more information and examples for citing dictionaries, encyclopedias or multi-volume reference works.
For more information on reference list format and style, see General information - basics of referencing.
1. Author/s. Entry Title. Book Title, edition number ed.; Editor(s), Ed(s).; Publisher: Place of Publication (if needed), Year; Volume Vol., Pages pp. DOI
2. Author/s. Entry Title. Book Title, edition number ed.; Editor(s), Ed(s).; Publisher: Place of Publication (if needed), Year; Volume Vol., Pages pp. URL
1. Pohanish, R. P. Azobenzene. Sittig’s Handbook of Toxic and Hazardous Chemicals and Carcinogens, 6th ed.; William Andrew (Elsevier), 2012; Vol. 1, pp 301−302. https://doi.org/10.1016/B978-1-4377-7869-4.00001-1
2. Hamnett, A. Fundamentals of Electrochemistry. Encyclopedia of Chemical Physics and Physical Chemistry; Moore, J. H., Spencer, N. D., Eds.; CRC Press, 2021; Vol. 1. https://www.taylorfrancis.com/
1. Entry Title. Book Title, edition number ed.; Editor(s), Ed(s).; Publisher: Place of Publication (if needed), Year; Volume Vol., Pages pp. DOI or URL
1. Spectrum. A Dictionary of Chemistry, 8th ed.; Law, J., Rennie, R., Eds.; Oxford University Press, 2020. https://doi.org/10.1093/acref/9780198841227.001.0001
1. Entry Title. Wikipedia. URL (accessed YYYY-MM-DD)
1. Acetaldehyde. Wikipedia. https://en.wikipedia.org/wiki/Acetaldehyde (accessed 2025-06-04)
Put a superscript number in your text to show when you are using another person's ideas or words. This number directs the reader to the reference list, containing information about the work you are citing. If the reference is referred to again, the same number is used.
... has been recently identified.1
If you are making a direct quotation, use quotation marks.
Dalas and Koutsoukos observed that "the presence of the magnetic field did not result in preferential growth of a certain crystal face."2
If the same source is referred to more than once within your text, repeat the number. If you are expressing ideas that have originated from more than one source, separate the numbers with commas, or use a hyphen if referring to several endnotes. A number following the full stop/period applies to the whole sentence.
...in alkyl sulphates such as sodium lauryl sulphate3,5-7 and diethyl sulphate6. Chew and Maibach3 also noted that the compounds showing promise were those in the C12 - C14 range.