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.
When the airway is blocked, the blood absorbs the air inside the air sacs (alveoli). Without more air, the sac shrinks. The space where the lung was before the collapse fills up with blood cells, fluids and mucus. It may then become infected. Other factors can lead to a collapsed lung include: A plug of mucus, a tumor or something breathed into the lungs.