Self-study sounds like a great idea, especially as Chemistry appears to be an area of his personal interest. Khan Academy is usually quite good. A collection of online resources is also found at HippoCampus.

As the prerequisite Honors Chemistry course may vary, and AP Chemistry is subject to changes by College Board, there may not be a definitive answer to your question. That said, here are some resources to examine:

- Your local high school course catalog (high level description of Honors Chemistry) and the Honors Chemistry course syllabus (detail description).

- The source of AP Chemistry: the website of the College Board. There are several web pages for students, which are dedicated to AP Chem class information and AP Chem exam information. Information for teachers/schools can also be found, regarding the college board "audit process". For example, one college board web page refers readers to the Learning List website, and lists several possible AP Chem textbooks.

- Old text books and exam prep guides can often be found at used book stores.