Early versions did not list an element for every atomic number.

早期的版本并没有为每个原子序数列出一个元素。

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Then, there'd be an atomic number, for which there was no known element.

然后会出现原子序数，代表了未知元素。

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In each period, the atomic number of each element is increasing.

每个周期中元素的质子数从左到右递增。

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In each period, the atomic number of each element is increasing.

每个周期中元素的质子数从左到右递增。

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