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现行国际原子量是以~(12)C=12为基准的各种元素质量的相对平均比较值。它是没有量纲的。它是按该元素各种天然同位素丰度计算得到的平均值,其具体数值就等于摩尔质量(克)。现知20种元素只有一种天然同位素,其原子量可以直接精确测定,精确度可达百万分之一。但是多数元素都有几种天然同位素,不同试样的同位素丰度还可能略有差别。现知31种元素因同位素丰度不同而导致了原子量值的不确定性。国际纯粹与应用化学联合会
The current international atomic weight is the relative average comparison value of various elemental masses based on ~ (12) C = 12. It is dimensionless. It is based on the elements of various natural isotope abundance calculated average, the specific value is equal to the molar mass (g). Now known only 20 kinds of natural isotope elements, the atomic weight can be directly and accurately measured, the accuracy of up to one millionth. However, most elements have several natural isotopes and the isotopic abundances of different samples may differ slightly. It is known that the 31 elements have different atomic weight values due to their different isotopic abundances. International Union of Pure and Applied Chemistry