The mole concept pervades all of chemistry. Since most quantitative chemical calculations are based on the mole, an understanding of the mole is essential to the study of chemistry. An understanding of how the mole relates to mass, number of entities (atoms, molecules, ions, etc.) and volume of a gas is included in this module. Formulas are most often interpreted in terms of moles rather than atoms, molecules or formula units (see Language of Chemistry section) since chemical reactions are generally carried out on a macroscopic scale.
The SI definition of mole is: "... the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kg of carbon 12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles."
Chemists use the mole (symbolized mol) to express amount of substance (elements, compounds, ions, electrons, etc.). Avogadro's number (6.02 x 1023 ) is the number of entities in one mole of a substance. Because it is easier to weigh large numbers of particles than to count them, chemists generally relate moles of a substance to mass rather than to the number of particles. The molar mass (mass of one mole) of a substance is the sum of the relative atomic masses (in grams) of the elements in a formula unit of the substance. Avogadro's number of formula units of a substance has a mass equal to the molar mass of the substance.
The subscripts in a formula can be interpreted as the number of moles of the element present in a mole of the compound. Calculations involving percent composition of a compound and empirical formula involve the mole concept. (The relationship of moles to stoichiometry is the subject of another SourceBook module.)
This topic lends itself to a historical presentation (see History section).
After completing their study of the mole concept, students should be able to:
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