What is the sum of the atomic masses of all atoms in a compound as given in its chemical formula called?

• A. Formula Mass
• B. Atomic Mass
• C. Law of Definite Composition
• D. Octet Rule

Answer: (A)

Think of the chemical formula as a recipe that lists how many atoms of each element are in one formula unit. To find the total mass, multiply each element’s atomic mass by how many atoms of that element are present, then add all those amounts together. That sum is called the formula mass. It represents the mass contributed by one formula unit in atomic mass units; if you convert to grams per mole, you’re talking about the molar mass, which is numerically the same value. The other ideas aren’t about summing up the masses in a compound—atomic mass is the mass of a single atom, the law of definite composition describes fixed elemental ratios, and the octet rule is about electron arrangements.