The weight-formula and the molecular mass
If we add the masses of the atoms of the chemical formula of a compound we obtain its formula weight.
If the formula also represents a real molecule, we can talk about molecular mass.
To calculate the weight-formula of a compound we need the periodic table, where the atomic weights
of all the chemical elements are collected.
Example 1
Sodium bicarbonate: πππ»πΆπ3
Formula weight = 23.0 + 1.0 + 12.0 + 3 β 16.0 = 84.0 uma
In this case the formula represents a crystal lattice, but not a molecule.
Example 2
Water: π»2 π
Formula weight = 2 β 1.0 + 16.0 = 18.0 uma
Since the formula does represent a real molecule, we can say that the molecular mass of water is 18.0
amu.