Quantum mechanics helps us to understand how energy is used or released by atoms. Negatively charged electrons circle about the positively charged nucleus of the atom. They stay in the same orbit, until this is disturbed, and each orbit has its own level of energy. If more energy is added, when the atom is heated or when light shines on it, the electron jumps out to another orbit, absorbing the extra energy. Then when it drops back again to its original orbit, it releases this energy as heat or light. This tiny packet of energy is called a quantum. Heisenberg’s Uncertainty Principle states that it is not possible to measure exactly where a subatomic particle is and how fast it is moving, because any attempt to measure it will disturb the particle and change its characteristics.
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