Formula mass, also known as molecular weight, is calculated by summing the average atomic masses of all atoms in a molecule's formula. You can find the average atomic mass, also known as the mass number, of each element on the periodic table. For example, the formula mass of water (H₂O) is calculated by adding the atomic masses of two hydrogen atoms (1.008 amu each) and one oxygen atom (15.9994 amu), resulting in a formula mass of 18.0152 amu.
Formula mass is expressed in atomic mass units (amu), which represent the mass of a single atom of carbon-12. However, chemists often work with gram quantities and report formula mass in grams per mole (g/mol).
Examples:
- Water (H₂O): 2(1.008 amu) + 15.9994 amu = 18.0152 amu
- Sodium chloride (NaCl): 22.990 amu + 35.453 amu = 58.443 amu
- Glucose (C₆H₁₂O₆): 6(12.011 amu) + 12(1.008 amu) + 6(15.9994 amu) = 180.156 amu
