Hello, I am a high school student looking for resources to prepare for the US National Chemistry Olympiad. I have already taken AP Chemistry (although my teacher did not cover a few topics, such as coordination compounds) and I did well in the class and on the exam. At this point, I need a book/website that can provide me with the content that is not present in an average AP-level book. Could someone recommend a textbook that would be helpful? Also, is anyone aware of a source of olympiad-level problems that I could use to practice (other than the official website, which I'm already aware of?) Thank you.