What does et al. mean?
Often seen in reference lists for a variety of different styles, et al. is a common abbreviation from the Latin "et alia" (gender neutral), "et alii" (masculine), or "et aliae" (feminine). It means "and others", or "and all the rest".
When is it used?
Et al. is used with a very long list of authors to indicate that there are more contributors not specifically listed. While the ACS Style Guide generally recommends listing all authors (Chapter 14, page 291), some journals ask for only a certain number of listed authors before using et al., so check the requirements of the publication.
Where is the punctuation?
Since only "alia" is abbreviated, it gets the period. Putting the period after "et" is a common mistake.
This Grammarly post does an illustrated explanation: https://www.grammarly.com/blog/et-al/
Collate all references at the end of the manuscript:
Book Chapter (from an edited book)
ACS Style Guide, 3rd Edition
Effective Communication of Scientific Information
Editor(s): Anne M. Coghill, Lorrin R. Garson
Publication Date (Print): June 01, 2006
Copyright © 2006 American Chemical Society
Part 1. Scientific Communication
1-1: Ethical Guidelines to Publication of Chemical Research
3-1: Proofreaders’ Marks
5-1: Online Submission at Selected Scientific Publishers and Research Grant Agencies
5-2: Key Features of Selected Online Submission Systems
8-1: The IUPAC International Chemical Identifier, InChI
Part 2. Style Guidelines
9-1: Recommended Spelling List
10-1: Computer and Internet Terms
10-2: Abbreviations, Acronyms, and Symbols
11-1: The International System of Units (SI).
12-1: End-of-Line Hyphenation of Chemical Names
12-2: Representation of Combinatorial Chemistry
12-3: CAS Registry Numbers
13-1: Symbols for Commonly Used Physical Quantities
13-2: The Crystallographic Information File
14-1: CASSI Abbreviations for the 1000+ Most Commonly Cited Journals
14-2: A Sample CASSI Entry