How to Cite in ACS Style: A Complete Guide With Examples

When you write a scientific paper in chemistry, you need a citation style that handles journal articles, patents, and technical reports clearly. The American Chemical Society (ACS) style is the standard format for chemistry and related fields. To cite in ACS style, you include a numbered reference in the text that points to a full citation in the bibliography. The superscript number goes at the end of the relevant sentence or clause, and the bibliography entry lists the author names, article title, journal abbreviation, year, volume, and page numbers.

The Three In-Text Citation Systems

ACS style gives you three ways to mark citations in your text. Pick one system and use it consistently throughout your paper.

Superscript Numbers

This is the most common system in ACS journals. You place a superscript number at the point where you reference a source. The number goes after punctuation marks, including periods and commas.

Example: The reaction was carried out under an inert atmosphere.¹

If you cite the same source more than once, you reuse the same number. The first source you cite gets number 1, the second gets number 2, and so on.

Italic Numbers in Parentheses

Instead of superscript, you can use italic numbers inside parentheses. This system works well if your word processor does not handle superscript formatting easily.

Example: The catalyst was added slowly (1).

Author-Date System

Some ACS publications use an author-date format. You include the author’s last name and the publication year in parentheses.

Example: The mechanism was confirmed by a later study (Smith, 2020).

The corresponding bibliography entry then lists the full citation alphabetically by the author’s last name.

How to Format the Reference List

The reference list appears at the end of your paper with the heading “References” or “Literature Cited.” The formatting depends on which in-text system you used.

For Numbered References

List entries in the order they first appear in the text. Each entry starts with the number in bold or plain text, followed by a period.

The general format for a journal article is:

1. Author Last Name, First Initial; Author Last Name, First Initial. Article Title. Journal Abbreviation Year, Volume, Page Numbers.

Example:

1. Miller, J. A.; Thompson, R. L. Synthesis of Substituted Pyridines. J. Org. Chem. 2021, 86, 1234-1245.

The journal title is abbreviated according to the Chemical Abstracts Service Source Index (CASSI). The year is in bold, the volume is in italics, and the page numbers are not formatted.

For Author-Date References

List entries alphabetically by the author’s last name. The format is similar but puts the year right after the author names.

Example:

Miller, J. A.; Thompson, R. L. Synthesis of Substituted Pyridines. J. Org. Chem. 2021, 86, 1234-1245.

Common Reference Types

Book:

Author Last Name, First Initial. Book Title; Publisher: Location, Year; pp Pages.

Example:

Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry, 2nd ed.; Oxford University Press: Oxford, 2012; pp 145-160.

Website:

Author Last Name, First Initial. Page Title. Website Name, URL (accessed Date).

Example:

National Institute of Standards and Technology. Benzene. NIST Chemistry WebBook, https://webbook.nist.gov/cgi/cbook.cgi?ID=C71432 (accessed March 15, 2024).

For a website without a clear author, start with the organization name.

Patent:

Inventor Last Name, First Initial. Patent Title. Patent Number, Date.

Example:

Smith, A. B. Method for Purifying Proteins. US Patent 9,876,543, 2019.

Specific Rules and Examples for Common Cases

Multiple Authors

For up to ten authors, list all names in the reference. Separate names with semicolons. For more than ten authors, list the first ten followed by “et al.”

Example (three authors):

1. Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula. Phys. Rev. B 1988, 37, 785-789.

No Author Listed

If a source has no named author, start the reference with the article title or the organization name.

Example:

The Merck Index, 15th ed.; Royal Society of Chemistry: Cambridge, 2013.

Citing Multiple Sources in One Place

When you need to cite several sources for a single statement, combine them in one set of brackets or parentheses. For superscript numbers, list the numbers separated by commas without spaces. For consecutive numbers, use a hyphen.

Example: Several recent studies support this finding.¹⁻³

In the author-date system, list the sources in alphabetical order separated by semicolons.

Example: Several recent studies support this finding (Miller, 2021; Smith, 2020).

Key Takeaways

• ACS style uses three in-text citation systems: superscript numbers, italic numbers in parentheses, or author-date. Pick one and use it consistently.
• The reference list format differs depending on the in-text system. Numbered references go in order of appearance; author-date references are alphabetical.
• Journal article citations need author names, article title, journal abbreviation (CASSI), year, volume, and page numbers.
• For websites, include the URL and the date you accessed the page.
• Always check the specific instructions from your instructor or the target journal, as some details may vary.