I am trying to cite, using the ACS format, https://www.intechopen.com/books/cancer-causing-substances/heavy-metals-and-cancer, but I don't know whether it is considered a book or ebook chapter. How am I supposed to tell them apart? The link is under "books" on the website, but seeing as it is online, wouldn't it be considered an ebook? If I cite it as a book, it'll be pretty weird for me to include a link and the date accessed, won't it?
I would cite this as a book section, including the DOI (because that's where you found it/how others will be able to find it) but not including "date accessed", because that is intended for more volatile resources like web pages. (If a reference has a DOI you can usually treat it as non-volatile.)
Sticking as precisely as you can to a reference format is important, but the most important thing is to make sure that the information is present that allows readers to (1) attribute credit appropriately and (2) re-locate the original source.
(1) Carver, A.; Gallicchio, V. S. Heavy Metals and Cancer. In Cancer Causing Substances; Atroshi, F., Ed.; 2018. https://doi.org/10.5772/intechopen.68247.