在化学性质相似的同族元素中，质量越重带的正电越强。
In all groups of chemically similar elements the heaviest are the most electropositive.
钡、锶属于同族元素，性质相似，分离困难。
Barium and strontium belong to one family, they were some alike in nature and difficult to be separated.
区元素同族内某些性质的起伏变化称之为第二周期性。
The second periodicity of element is rise and fall of some properties in elements of the same clan in Parea.
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