The term UNIT CHEM can be broken down into two parts: MOL, which is a three letter acronym, and UNIT, which is a four letter word. MOL stands for 'MOLECULE, ' which is the smallest UNIT of matter that can exist independently. A MOLECULE is composed of atoms, which are the basic building blocks of all matter. UNIT refers to a UNIT of measurement, such as a meter or a liter. In chemistry, units are used to measure the amount of a substance, such as the number of atoms or molecules in a given sample. Together, UNIT CHEM refers to the measurement of the number of molecules in a given sample.