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.
Air travels along passageways in the lungs to deliver oxygen to the blood. During an asthma attack, a thick, slippery substance called mucus blocks the lung passages, swelling occurs, and lung muscles squeeze on the airways. Breathing becomes difficult. Such episodes don't usually happen out of the blue. At least half of the people who suffer from asthma have allergies that can trigger an attack, says Sam Arbes.