- Gram
- Liter
- Mole
- Newton
The mole (symbol: mol) is the SI base unit for measuring amount of substance, defined as containing exactly 6.02214076 × 10²³ elementary entities (atoms, molecules, ions, electrons, or other particles). This number, called Avogadro’s constant (named after Amedeo Avogadro), was established as a fixed value in the 2019 redefinition of SI units. One mole of any substance has a mass in grams numerically equal to its atomic or molecular mass (the molar mass). For example, carbon-12 has a molar mass of exactly 12 g/mol by definition, containing 6.02214076 × 10²³ atoms. The mole enables chemists to count particles by weighing macroscopic quantities, bridging the atomic scale and laboratory scale. It is fundamental in stoichiometry—calculating reactant quantities and product yields in chemical reactions. The concept originated from Avogadro’s hypothesis (1811) that equal volumes of gases contain equal numbers of molecules under same conditions. Understanding the mole is essential for quantitative chemistry, from solution concentration calculations (molarity) to gas law applications and thermodynamic computations.
