Molecular weight

The molecular weight of a molecule is the sum of the atomic weights of the elements that constitute the molecule. Essentially, molecular mass or molecular weight is the mass of a molecule.

Example 1: Molecular weight of water (H2O)

 2 Hydrogen atoms  2 X 1  2
 1 Oxygen atom  1 X 16  16
 Molecular weight of H2O  18

Example 2: Molecular weight of sodium bicarbonate (NaHCO3):

 1 Sodium atom  1 X 23  23
 1 Hydrogen atom  1 X 1  1
 1 Carbon atom  1 X 12  12
 3 Oxygen atoms  3 X 16  48
 Molecular weight of NaHCO3  84

Molecular weight, like atomic weight, is expressed simply as a figure without a unit.