As of 2020, the ACS Guide to Scholarly Communication is a digital-first publication containing a wealth of new chapters and resources to help you master the art of scholarly communication and make your research stand out. This publication includes the most updated version of the ACS Style Guide.
The American Chemical Society (ACS) has its own style guide. There are two copies of this style guide in the Angus L. Macdonald Library, one in the Reference Collection and another in the Main Collection, under the call number QD 8.5 A25. Chapter 14 which describes references and referencing is available online.
There is an excellent quick guide for the ACS style at Williams College Library.