What is capable of taking up, or of uniting with, certain other elements or compounds, without the elimination of any side product; thus, aldehyde, ethylene, and ammonia are unsaturated called?

unsaturated — (Chem.) Capable of taking up, or of uniting with, certain other elements or compounds, without the elimination of any side product; thus, aldehyde, ethylene, and ammonia are unsaturated. (Webster's 1913.)

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