What is molecular mass, and how is it calculated?

Molecular mass is the sum of the atomic masses of all atoms in one molecule of a substance, expressed in atomic mass units (u) or g/mol.

Example: Water (H₂O):

Steps: Write formula → count atoms → multiply by atomic mass → add all values.

Molecular mass is calculated by adding the atomic masses of all atoms in a molecule, using their quantities as per the formula.