AAAS: THE PHYSICAL SETTING: ENERGY TRANSFORMATIONS - When energy of an isolated atom or molecule changes, it does so in a definite jump from one value to another, with no possible values in between
When energy of an isolated atom or molecule changes, it does so in a definite jump from one value to another, with no possible values in between. The change in energy occurs when radiation is absorbed or emitted, so the radiation also has distinct energy values. As a result, the light emitted or absorbed by separate atoms or molecules (as in a gas) can be used to identify what the substance is.