uranium (yōrāˈnēəm) [key], radioactive metallic chemical element; symbol U; at. no. 92; mass number of most stable isotope 238; m.p. 1,132°C; b.p. 3,818°C; sp. gr. 19.1 at 25°C; valence +3, +4, +5, or +6.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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