1 mol = 6.022 × 10²³ particles = M grams = 22.414 L at STP
The mole is the SI unit for amount of substance. One mole contains exactly 6.02214076 × 10²³ entities (Avogadro's number, NA). This number was chosen so that 1 mol of ¹²C atoms has a mass of exactly 12 g. Key relationships: mass = n × M (molar mass), number of particles = n × NA, volume of ideal gas at STP = n × 22.414 L. The mole bridges the atomic scale (amu) and the macroscopic scale (grams): 1 amu × NA = 1 g. Examples: 1 mol H₂O = 18.015 g = 6.022 × 10²³ molecules = 3 × 6.022 × 10²³ atoms. The mole concept is the foundation of all quantitative chemistry — from balanced equations to titrations to industrial synthesis.