The terms "formula weight" and "atomic mass unit" (amu) refer to different concepts used in chemistry to express the mass of atoms and molecules.
Formula Weight: Formula weight, also known as molecular weight or molar mass, is the mass of a molecule or compound expressed in atomic mass units (amu) per molecule. It is calculated by summing up the atomic masses of all the atoms in a chemical formula. The atomic masses used in the calculation are based on the average mass of the isotopes of the elements, taking into account their natural abundances.
For example, let's consider water (H2O). The formula weight of water can be calculated by adding the atomic masses of two hydrogen atoms and one oxygen atom: Formula weight of water = (2 * atomic mass of hydrogen) + (1 * atomic mass of oxygen)
Atomic Mass Unit (amu): An atomic mass unit (amu) is a unit of mass used to express the mass of atoms or subatomic particles. It is defined as one-twelfth the mass of a carbon-12 atom. The atomic mass unit provides a relative scale for comparing the masses of different atoms.
For example, the atomic mass of hydrogen is approximately 1.008 amu, while the atomic mass of oxygen is approximately 15.999 amu.
In summary, formula weight is the mass of a molecule or compound expressed in amu per molecule, obtained by summing up the atomic masses of its constituent atoms. Atomic mass unit (amu), on the other hand, is a unit of mass used to express the mass of individual atoms or subatomic particles.