View full lesson: http://ed.ted.com/lessons/why-don-t-oil-and-water-mix-john-pollard Salt dissolves in water; oil does not. But why? You can think of that glass of water as a big, bumpin' dance party where the water molecules are always switching dance partners -- and they'd much rather dance with a salt ion. John Pollard explains how two chemistry principles, energetics and entropy, rule the dance floor. Lesson by John Pollard, animation by Andrew Foerster.