The terms molecular mass, formula mass, molar mass, and atomic mass are related but have distinct meanings in chemistry. While weight and mass are often used interchangeably in everyday language, in scientific contexts, they have different definitions.
Molecular Mass: Molecular mass refers to the sum of the atomic masses of all the atoms in a molecule. It is typically expressed in atomic mass units (amu) and is used to determine the mass of a specific molecule.
Formula Mass: Formula mass is similar to molecular mass, but it is used for ionic compounds and covalent compounds without distinct molecular structures. It represents the sum of the atomic masses of all the atoms in a chemical formula. Formula mass is also expressed in atomic mass units (amu).
Molar Mass: Molar mass refers to the mass of one mole of a substance. It is calculated by summing the atomic masses of all the atoms in a formula or molecule. Molar mass is expressed in grams per mole (g/mol) and is used to convert between mass and the number of moles of a substance.
Atomic Mass: Atomic mass refers to the mass of a single atom of an element. It is typically expressed in atomic mass units (amu) and represents the average mass of all the isotopes of an element, taking into account their relative abundances.
As for the use of weight instead of mass, it depends on the context. In scientific terms, mass is the measure of the amount of matter in an object, while weight is the force exerted on an object due to gravity. However, on Earth's surface, the weight of an object is often directly proportional to its mass, so the terms weight and mass are sometimes used interchangeably, especially in everyday language. In scientific calculations, it is generally more appropriate to use the term mass.