What are reference books?
Reference books are things like encyclopedias, dictionaries, and handbooks. They give you a nice background and some quick facts about your topic.
Wikipedia is a great source of background information. The worry by some librarians and professors is that there is little control over changes made to entries. That being said, Wikipedia can be still be a useful tool. I like to use it for the suggestions for further reading and looking at the reference section (just like reading any article, the references can sometimes be the best part).
Check out the Chemistry Portal from Wikipedia.