Chemistry : Molecular Weights of Chemical Compounds

How to Calculate the Molecular Weight of a Chemical Compound?

The Molecular Weight (also referred to as the Formula Weight) of a chemical compound is calculated by adding the atomic weights of the atoms (elements) that constitute the compound.

Example:
What is the molecular weight of Sodium Carbonate [Na₂CO₃] ?
Given Atomic Weights: C = 12 ; O = 16 ; Na = 23

Molecular weight of Na₂CO₃
= (2 x Atomic weight of Na) + Atomic weight of C + (3 x Atomic weight of O)
= (2 x 23) + 12 + (3 x 16) = 106

Note that the Atomic Weight (also referred to as the Relative Atomic Mass) of an element is the number of times an atom of an element is heavier than an atom of hydrogen. Thus, hydrogen is treated as the reference, whose atomic weight is taken as 1.

Practice Exercise for Chemistry Module on Molecular Weights of Chemical Compounds