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They were long believed to be totally unreactive but compounds of xenon, krypton, and radon are now known.

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Chemically they show variable valence and a strong tendency to form coordination compounds, and many of their compounds are colored.

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They are all radioactive, the heavier members being extremely unstable and not of natural occurrence.

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any of the series of fifteen metallic elements from lanthanum to lutetium in the periodic table.

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1. They are reactive, electropositive, divalent metals, and form basic oxides that react with water to form comparatively insoluble hydroxides.

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Definition of alkaline earth metal. : any of the divalent strongly basic metals of group II of the periodic table comprising beryllium

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a number of people or things that are located close together or are considered or classed together.

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a length or portion of time.