n. Symbol Fr An extremely unstable radioactive element of the alkali metals, produced by alpha decay of actinium or artificially from thorium, having over 40 isotopes and isomers, the most stable of which is Fr-223 with a half-life of 22 minutes. Atomic number 87; melting point 27°C; boiling point 677°C; valence 1. See Periodic Table. [After France.] |
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.