 Amount of substance

Amount of substance measures a count of specified entities, such as chemical atoms, molecules, ions, or Electrons, using the mole as its SI base unit. It differs from mass: equal amounts of substance of different chemical substances contain equal entity counts but generally have different masses. If $N$ entities are present, $n=N/N_{\mathrm{A}}$, where $N_{\mathrm{A}}$ is the Avogadro constant. The specified entity matters: one mole of water molecules contains two moles of hydrogen chemical atoms. ^[ref]

The amount of substance is a fundamental physical quantity that quantifies the quantity of entities, such as atoms, molecules, or particles, in a given sample. It is represented by the symbol \( n \) and is measured in moles (mol). One mole of a substance contains exactly \( 6.022 \times 10^{23} \) entities, a number known as Avogadro's number.