元素周期系是按照一定的标准（元素核电荷数的增加或者最初相对原子量的增加等）把化学元素排成序列，元素的性质在序列中呈现周期性的变化。
元素周期系 [yuán sù zhōu qī xì]
双语例句原声例句
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在太阳和行星形成之前，所有元素周期表上的化学元素在太阳系的原始尘埃中四处漂浮着。
Before the formation of the sun and planets, all the chemical elements found on the periodic table were floating around in the primordial dust of the Solar System.
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So, remember when you're looking at your periodic table, don't forget about the lanthanides, sometimes they come into play.
因此，要记住，当你在看元素周期表时，不要忘了镧系元素，有时候也会用到它们。
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- 来自原声例句