Avogadro's Number
Definition
The number of particles in one mole: 6.022 x 10^23. It lets chemists convert between the particle world and grams on a balance.
Symbol: · Unit: mol^-1
Technical definition
Avogadro's number is the exact constant 6.02214076 x 10^23 per mole, defining the number of constituent particles in one mole of substance. It was historically tied to the number of atoms in 12 grams of carbon-12.
Example
One mole of helium contains 6.022 x 10^23 helium atoms, and one mole of carbon dioxide contains 6.022 x 10^23 CO2 molecules.
Common confusion
Avogadro's number is not the same as a mole. It is the conversion factor (particles per mole), while the mole is the unit of amount.