Avogadroszám

Avogadroszám, abbreviated NA, is the number of elementary entities in one mole of a substance. It is a fundamental physical constant linking the macroscopic amount of matter to the microscopic particles that compose it. By definition, one mole contains NA particles, so the number of particles N is equal to the amount in moles n multiplied by NA (N = n × NA). The current value is exactly 6.02214076 × 10^23 mol^-1.

The constant is named after Amedeo Avogadro, whose 1811 hypothesis posited that equal volumes of gases at the same temperature and pressure contain the same number of particles. In 2019, the mole was redefined by fixing NA at exactly 6.02214076 × 10^23 mol^-1, making Avogadroszám an exact quantity.

Applications: NA is used to convert between moles and numbers of particles, to determine molar masses, and in calculations across chemistry, physics, and materials science. For example, one mole of any substance contains NA particles, so 2.00 moles contain 2 × NA particles.

Notes: The mass of one mole of carbon-12 is defined as exactly 12 g, linking NA to practical mass measurements, but NA remains an intrinsic fixed constant independent of any particular material.