| 单词 | 极不稳定 |
| 释义 | 〔francium〕An extremely unstable radioactive element of the alkali metals, produced artificially from actinum or thorium, having approximately 19 isotopes, the most stable of which is Fr 223 with a half-life of 21 minutes. Atomic number 87; valence 1. See table at element 钫：从碱金属锕或钍中人工提炼出的一种极不稳定的放射线元素，约有19种同位素，其中最稳定的是半衰期为21分钟的Fr223。原子序数为87；化合价为1 参见 element〔astatine〕A highly unstable radioactive element, the heaviest of the halogen series, that resembles iodine in solution. Its longest lived isotope has a mass number of 210 and has a half-life of 8.3 hours. Atomic number 85; melting point 302°C; boiling point 337°C; valence probably 1, 3, 5, 7. See table at element 砹：极不稳定放射性元素，在卤族元素比重最大，在溶解状态与碘相象，它最长周期的同位素原子量为210，半衰期为8.3小时。原子序数85；溶点302°C；沸点337°C；化合价可能为1、3、5、7 参见 element |
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