Chem1 Concept Builder

From site:  The Chem1 Concept Builder provides guided, interactive, and in-depth instruction in General Chemistry at the college and advanced-high school levels.

Guided: Each lesson focuses on a single concept which is introduced at the simplest possible level and is then extended step by step as you proceed, building on and reinforcing what you have already learned.

Interactive: No clunky Web-based interface. You are an active participant in a conversation that provides instantaneous feedback about your right and wrong answers, and multiple levels of help when you need it.

In-depth: Much more than the usual problem drills and multiple-choice tests; these lessons focus on the fundamental concepts to extend your understanding and to deal confidently with those problems you have not yet seen!

The Chem1 Virtual Textbook:  Well, it's not really a textbook, but rather a set of chapters covering many of the principal topics that are part of most first-year college-level or AP chemistry courses. They provide somewhat more depth than you will find in conventional textbooks, and will probably be most useful when used to supplement such texts. Many of the chapters contain the same illustrations and problem examples that you will encounter in the Chem1 lessons.