Materials Science Glossary - Q

quantum mechanics. A branch of physics that deals with atomic and subatomic systems; it allows only discrete values of energy that are separated from one another. By contrast, for classical mechanics, continuous energy values are permissible.

quantum numbers. A set of four numbers, the values of which are used to label possible electron states. Three of the  quantum numbers are integers, which also specify the size, shape, and spatial orientation of an electron’s probability density; the fourth number designates spin orientation.