the sum of the atomic weights in a molecule. For example, the molecular weight of water is 18, because the atomic weight of each of the hydrogen molecules is 1 and the atomic weight of oxygen is 16. See mole
molecular mass. Compare with formula weight and molecular formula. The average mass of a molecule, calculated by summing the atomic weights of atoms in the molecular formula. Note that the words mass and weight are often used interchangeably in chemistry.
the mass of a single molecule of a given compound. In the case of large molecules, it is usually expressed in kiloDaltons ( kD). In the case of significantly smaller molecules, it is expressed in atomic mass units.
The weight of a molecule expressed on a scale in which the carbon isotope weighs exactly 12.0; represents the sum of the weights of all the atoms in a molecule. As air is a gas mixture, it does not have a true molecular weight, but an apparent molecular weight determined by the percentages of the molecular weights of each gas in a composition.