molecular energy level. (physical chemistry). One of the states of motion of nuclei and electrons in a molecule, having a definite energy, which is allowed by quantum mechanics.1  Facebook.olecular energy level. (physical chemistry). One of the states of motion of nuclei and electrons in a molecule, having a definite energy, which is allowed by quantum mechanics. 1  Facebook.
Air first enters your body through your nose or mouth, which wets and warms the air. (Cold, dry air can irritate your lungs.) The air then travels through your voice box and down your windpipe. The windpipe splits into two bronchial tubes that enter your lungs.
If you do hold your breath, the loss of external pressure would cause the gas inside your lungs to expand, which will rupture the lungs and release air into the circulatory system. The first thing to do if you ever find yourself suddenly expelled into the vacuum of space is exhale.