Elements Without a Standard Atomic Weight
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Elements whose isotopes are all radioactive have no natural abundance to average, so tables list their most stable isotope's mass number instead.
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Technetium, promethium, and most elements from polonium onward show this mass number in brackets, not a weighted average.
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A bracketed number is not an atomic weight — it is one isotope's mass number, not a mass in grams.
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- Nothing yet depends on this.