How to Cite References in ACS Format: A Complete Guide
The ACS (American Chemical Society) style is the standard citation format for chemistry and related scientific fields. To cite references in ACS format, you place a number in superscript or parentheses at the point of citation in your text, then list the full reference with that same number in a “References” section at the end of your document.
The ACS Numbered Citation System
ACS style uses a numbered reference system. Each source you cite gets a unique number based on the order it first appears. The first source is number 1, the second is number 2, and so on. If you cite the same source again, you reuse the original number.
There are three accepted ways to indicate the citation number in your text:
Superscript numbers are the most common method. You place the number slightly above the line of text, usually at the end of the sentence or clause.
The reaction rate was found to depend on temperature.¹
Italic numbers in parentheses are also acceptable.
The reaction rate was found to depend on temperature (1).
Italic numbers in brackets are a third option.
The reaction rate was found to depend on temperature [1].
Whichever method you choose, use it consistently throughout your document. The corresponding full reference is listed under the same number in your “References” section.
Formatting Different Source Types
Journal Articles
For a journal article, the basic format includes author names, article title, journal abbreviation, year, volume, and page numbers.
Author 1; Author 2; Author 3. Journal Abbreviation Year, Volume, Pages.
Example:
Smith, J. A.; Jones, B. L. J. Am. Chem. Soc. 2021, 143, 1234-1240.
The journal title is italicized and abbreviated using standard chemical abbreviations. The year is bold, and the volume number is italicized. The issue number is usually omitted unless each issue starts on page 1.
Books
For a book, the format includes the publisher and city of publication.
Author 1; Author 2. Book Title; Publisher: City, State (or Country), Year.
Example:
Brown, T. L.; LeMay, H. E.; Bursten, B. E. Chemistry: The Central Science; Pearson: Boston, MA, 2018.
For a specific chapter from an edited book, include the chapter title and book editor.
Chapter Author 1; Chapter Author 2. Chapter Title. In Book Title; Editor 1, Editor 2, Eds.; Publisher: City, State (or Country), Year; pp Pages.
Websites
Citing a website requires the author (if known), page title, URL, and access date.
Author (if known). Page Title. URL (accessed Date).
Example:
American Chemical Society. Peer Review. https://www.acs.org/content/acs/en/peer-review.html (accessed 2024-01-15).
If no author is listed, start with the organization name.
Creating the References Section
Your “References” section comes at the end of your document. It should be titled “References” and left-aligned. The list is numbered sequentially to match your in-text citations.
Formatting rules:
- Entries are single-spaced, with a double space between each entry.
- The first line is flush left. Subsequent lines of the same entry are indented (hanging indent).
- List references in the order they first appear in your text, not alphabetically.
- Author names are listed as Last Name, First Initial. Middle Initial. Separate multiple authors with semicolons.
Example References section:
- Smith, J. A.; Jones, B. L. J. Am. Chem. Soc. 2021, 143, 1234-1240.
- Brown, T. L.; LeMay, H. E.; Bursten, B. E. Chemistry: The Central Science; Pearson: Boston, MA, 2018.
- American Chemical Society. Peer Review. https://www.acs.org/content/acs/en/peer-review.html (accessed 2024-01-15).
Handling Multiple Authors
For a source with up to ten authors, list every one. Separate names with semicolons, and place a period after the last author’s initials.
Smith, J. A.; Jones, B. L.; Lee, C. D.; Patel, R. K.; Williams, T. M.
For eleven or more authors, list the first ten names, then add a semicolon and “et al.”
Smith, J. A.; Jones, B. L.; Lee, C. D.; Patel, R. K.; Williams, T. M.; Garcia, S. P.; Miller, D. R.; Davis, K. L.; Rodriguez, L. M.; Chen, W. H.; et al.
Do not use “and” between author names. The semicolon is the standard separator.
Common Mistakes to Avoid
Inconsistent numbering. If you use superscript numbers in the text, do not switch to parentheses halfway through. Pick one method and stick with it.
Missing access dates for web sources. A URL alone is not enough. The access date tells your reader when you viewed the page.
Incorrect journal abbreviations. Many journals have standard abbreviations (J. Am. Chem. Soc. for Journal of the American Chemical Society). Use the abbreviation listed in the journal itself or in the ACS Chemical Abstracts Service Source Index (CASSI).
Forgetting the hanging indent. The first line of each reference should be flush left, with subsequent lines indented.
Listing references alphabetically. In ACS numbered style, the order is determined by first appearance in your text, not by author last name.
Key Takeaways
- Use a numbered citation system where each source gets a unique number based on the order it appears in your text.
- Indicate citations with superscript numbers, italic numbers in parentheses, or italic numbers in brackets.
- Format each reference according to its source type (journal article, book, website).
- Include an access date for any web source you cite.
- List references in numerical order, not alphabetical order, at the end of your document.
