Two online resources to help a student with high school level chemistry are chemtutor.com and the American Association of Chemistry Teachers website. Each website covers a wide variety of topics from the fundamentals to more advanced chemistry.
The American Association of Chemistry Teachers website covers high school topics such as atomic structures, chemistry basics, electrochemistry and kinetics. Each topic breaks down into lessons, including activities, labs, demonstrations and simulations.
Chemtutor.com is designed for high school and college students who need help with the fundamentals. Some of the topics covered on this website include elements, the periodic table, states of matter and reactions.