The weight of a molecule is by scientists on a relative scale. The weight of the molecule depends upon the weight of the atoms that form it. And the weight of the atom, in turn, depends upon the number of protons and neutrons in the nucleus of the atom.
A molecule of water is made up of two atoms of hydrogen plus one of oxygen. Hydrogen is a simple atom with only one proton in the nucleus. Its atomic weight is 1. The weight of other elements is in multiples of the weight of hydrogen. Oxygen has eight protons and eight neutrons, making an atomic weight of 16a So, water has a molecular weight of 2 1 plus 16, which makes its molecular weight 18.
Molecules are held in their places in a solid or a liquid by the forces of attraction between molecules. This attraction is of an electrical nature, and this force is strong enough to account for the strength of most solid materials.
How Do You Calculate Weight From Molecular Weight?
Using the periodic table of the elements to find atomic weights, we find that hydrogen has an atomic weight of 1, and oxygen is 16. In order to calculate the molecular weight of one water molecule, we add the contributions from each atom; that is, 2(1) + 1(16) = 18 grams/mole.