Generally speaking, Wikipedia, for most 'untargeted' topics such as the sciences, can be quite reliable and the more specific the topic, the Wikipedia entries tend to be written by the top experts in that field.
Wikipedia in its early years was regarded far less favourably than it is today due to its anyone-can-edit policy (I remember many, many years ago as a teaching assistant being instructed to deduct marks from lab reports when the student used Wikipedia as a reference, LOL). Now I think there are enough checks and balances in place, that for the most part the information can be trusted more than a lot of other internet sources where the information may be more one-sided and have a commercial slant trying to sell you something.
In general, now the topics on Wikipedia that can have unreliable information are those 'targeted' topics such as celebrities (eg. Justin Bieber) where certain people (immature youths) feel the impulse to edit the page for a laugh, but these pages get locked soon after. Also, contentious issues where an organization tries to maintain a certain image (eg. Church of Scientology) may try to manipulate its Wikipedia entry to push its agenda. Not to say it could not happen in science topics especially if you have different competing theories where the Wikipedia page will be written by different research groups trying to emphasize their theory, but usually the introduction entry on the page will be written in a way to let the reader understand that that topic has controversy and that any theory in regard to it is far from being universally accepted.
That said, another link you may be interested in trying to learn about general chemistry topics (which will be better focused and organized instead of the stream of consciousness flow of Wikipedia) is ChemWiki from UC Davis. http://chemwiki.ucdavis.edu/
edit: but what Dan said is true --- Textbooks are always going to be a better source for more detailed & concise, information than anything you can find on an internet webpage.