There are many handbooks, dictionaries, and encyclopedias that describe chemical terms, structures, data, etc. If you are not clear about your topic, try establishing its limits with a good definition and some introductory information.
AccessScienceCovers all of science; much information related to chemistry. Includes a scientific dictionary, images, and biographies of famous scientists. Also includes links to related websites.
CRC Handbook of Chemistry & PhysicsKey reference source for chemical and physical data--constants, properties, etc.
Dictionary of ChemistryContains entries for over 4200 terms related to chemistry.
Encyclopedia of Life ScienceA comprehensive life sciences resource on a variety of topics from biochemistry to virology. Links to relevant news/articles. Also includes illustrations, a glossary, and related web resources, as well as themed collections of articles.
Kirk-Othmer Encyclopedia of Chemical TechnologyComprehensive encyclopedia covering chemical technology, industrial processes and applications.