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Glossary
Mole
A mole (symbol mol) is the SI unit for amount of substance. It’s basically a counting unit—like “a dozen,” but unimaginably larger.
Formally (SI definition), 1 mol contains exactly 6.02214076 × 10^23 elementary entities. Those “entities” are whatever you specify: atoms, molecules, ions, electrons, or even a defined group of particles.
That exact number is tied to the Avogadro constant N A, which is fixed by definition in the modern SI. So the mole is now defined by an exact count, not by the mass of carbon-12 (older definition).