Francium, 87Fr|
Pronunciation | (FRAN-see-əm) |
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Mass number | 223 (most stable isotope) |
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Atomic number (Z) | 87 |
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Group | group 1 (alkali metals) |
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Period | period 7 |
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Block | s-block |
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Element category | alkali metal |
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Electron configuration | [Rn] 7s1 |
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Electrons per shell | 2, 8, 18, 32, 18, 8, 1 |
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Phase at STP | Fr: Solid |
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Melting point | 300 K (27 °C, 81 °F) |
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Boiling point | 950 K (677 °C, 1251 °F) |
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Density (near r.t.) | 2.48 g/cm3 (estimated) |
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Vapor pressure (extrapolated)P (Pa) | 1 | 10 | 100 | 1 k | 10 k | 100 k |
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at T (K) | 404 | 454 | 519 | 608 | 738 | 946 |
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Oxidation states | +1 (a strongly basic oxide) |
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Electronegativity | Pauling scale: >0.79 |
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Ionization energies | |
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Covalent radius | 260 pm (extrapolated) |
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Van der Waals radius | 348 pm (extrapolated) |
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Natural occurrence | Fr: From decay |
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Crystal structure | body-centered cubic (bcc) (extrapolated) |
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Thermal conductivity | 15 W/(m·K) (extrapolated) |
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Electrical resistivity | 3 µΩ·m (calculated) |
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Magnetic ordering | Paramagnetic |
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CAS Number | 7440-73-5 |
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Naming | after France, homeland of the discoverer |
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Discovery and first isolation | Marguerite Perey (1939) |
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Francium is a chemical element with the chemical symbol Fr and an atomic number of 87. It is a metal. In chemistry it is placed in a group of metal elements named the alkali metals. Francium is very radioactive. It is in very small amounts in uranium and thorium ores. It has the lowest electronegativity and electron affinity of all the chemical elements.
Francium reacts violently with water, as do all of the elements in group 1 on the periodic table.