(a) Molecular mass: The molecular mass of a substance is the sum of atomic masses of all the atoms in a molecule of the substance. It is used for those substances whose constituent particles are molecules.
For example: The molecular mass of CO2 = 1 × atomic mass of carbon + 2 × atomic mass of oxygen
⇒ 12 + 2 × 16
⇒ 12 + 32 = 44u
(b) Chemical formula: The chemical formula of a compound is a symbolic representation of its composition. The chemical formula for different compounds can be written easily. For writing a chemical formula, we need to learn the symbols and combining the capacity of elements.
For example, Chemical formula of carbon tetrachloride:
Valency of carbon is 4
Valency of chlorine is 1
Thus, the formula for carbon tetrachloride is CCl4.
(c) One mole of any species (atoms, ions or molecules) having that quantity in number having a mass equal to its atomic or molecular mass in grams.
