Hank discusses the arrangement of the atoms in crystalline solids and how their atomic arrangement differs from amorphous solids. He mentions that each category of solid's atomic arrangement affects its properties, from how it breaks to its appearance. He also describes a couple of types crystalline solids: ionic and molecular.
The Fantastic Four are battling Dr. Doom, who has turned into an organic metal capable of absorbing and manipulating electrical energy. They win the battle by exposing him to excessive heat and then cooling him down rapidly with water, turning him into a solid piece of metal.
Sheldon, Leonard, Howard, and Raj create an oobleck using corn starch and water. Initially, it's a liquid, but when they turn the music on, it resembles a solid. Sheldon explains the phenomenon to Penny: it's a non-Newtonian fluid which is liquid but becomes solid due to the percussion from the speaker.
Professor Philip Brainard creates Flubber and tries to learn more about it. He performs quick tests on the physical properties of Flubber and finds that it is a highly viscous elastomer that can also phase shift between a liquid and a solid. Using observation skills, he also learns that Flubber is moldable, foldable, ductile, and elastic, among other properties.