Physical and Theoretical Chemistry

Energy Is Everything

Can molecules have any arbitrary energy?

No, molecules actually have a discrete number of possible energy levels. Another way to say this is that their energies are quantized. To illustrate why this is so different from situations we’re used to in everyday life, consider what happens when you’re throwing a baseball. You could throw it at any speed between 0 meters per second (m/s) and however fast you are capable of throwing it. In molecules, though, only a discrete set of energies are possible. It’s as if you could throw the baseball either 2 m/s or 40 m/s, but not 20 m/s or any other speed in between. There aren’t many situations we encounter in everyday life in which the possible energies associated with objects come in a discrete set of values.


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