摩尔Mole

物质的量 n、粒子数 N 与阿伏伽德罗常数 N_A 的关系为 n = N/N_A；与质量的关系为 n = m/M，其中摩尔质量 M 以 g/mol 为单位时数值等于相对分子（原子）质量。理想气体在标准状况（0 °C、101.325 kPa）下摩尔体积约 22.4 L/mol。使用摩尔时必须指明基本单元，如 1 mol H₂ 与 1 mol H 不同。

Amount n relates to particle number N by n = N/N_A, and to mass by n = m/M, where the molar mass M in g/mol is numerically equal to the relative molecular (atomic) mass. An ideal gas at 0 °C and 101.325 kPa occupies about 22.4 L/mol. The entity must always be specified: 1 mol of H₂ is not 1 mol of H.

1894 年前后奥斯特瓦尔德从德语 Molekül（分子）造出 Mol 一词，表示以克为单位、数值等于分子量的物质质量。1971 年第 14 届国际计量大会把摩尔列为第七个 SI 基本单位，定义为 0.012 kg ¹²C 所含的原子数。

Around 1894 Ostwald coined Mol from German Molekül to denote a mass in grams numerically equal to the molecular weight. In 1971 the 14th General Conference on Weights and Measures adopted the mole as the seventh SI base unit, defined as the number of atoms in 0.012 kg of ¹²C.

为摆脱对实物标准的依赖，2019 年 5 月 20 日起摩尔改为由固定的阿伏伽德罗常数数值来定义，¹²C 的摩尔质量不再精确等于 12 g/mol，而是需要测量的量（仍极接近 12 g/mol）。这一常数值主要通过高纯 ²⁸Si 单晶球的 X 射线晶体密度法测定。

To remove dependence on a physical artefact, from 20 May 2019 the mole has been defined by a fixed numerical value of the Avogadro constant, so the molar mass of ¹²C is no longer exactly 12 g/mol but a measured quantity, still extremely close to it. The constant's value was fixed largely through X-ray crystal density measurements on highly enriched ²⁸Si spheres.