Do atoms gain or lose mass when they react with each other?

Atoms do not gain or lose mass when they react with each other. This is because no new atoms are created or destroyed during a chemical reaction. The total mass of atoms after the reaction is always equal to the total mass of atoms at the beginning of the reaction. This is in accordance with the Law of Conservation of Mass, which states that ‘mass cannot be created or destroyed but is simply transformed from one state to another’.