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许多元素的原子量并非固定不变,而是决定于元素材料的来源和处理的过程。表中的附注详细注解了各元素可能有的变化情况。本表提供的Ar(E)值应用于在地球上存在的天然元素和某些人工合成元素。各原子量数值最后一位数字至±1,带星号·的准至±3。括弧中的数值用于某些放射性元素,它们的准确原子量因与来源有关而无法提供,表中数值是该元素已知半衰期最长的同位素的原子质量数。
The atomic weight of many elements is not fixed but depends on the source of the elemental materials and the process of their disposal. The notes in the table detail the possible changes in each element. The Ar(E) values provided in this table apply to the presence of natural elements and some synthetic elements on Earth. The last digit of each atomic weight value is ±1, with an asterisk of ±5. Values in parentheses are used for certain radioactive elements. Their exact atomic weight is not available because of their source. The value in the table is the atomic mass number of the isotope known for the longest half-life of the element.