This isn't a super-exciting topic, but it will be on your quiz, so listen up!
Solid vs Liquid vs Gas
In Chemistry class it's easy for teachers to get so bogged down in the details of whatever vocabulary-packed topic you happen to be studying that the "big picture" goes unnoticed: ultimately, everything in chemistry is about bouncy little magnets (atoms and molecules) either sticking together (solid) or rattling apart (liquid and gas).
If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)