Francium,  ₈₇Fr

General properties
Pronunciation	/ˈfrænsiəm/ ​(FRAN-see-əm)
Mass number	223 (most stable isotope)
Francium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Cs ↑ Fr ↓ (Uue) radon ← francium → radium
Atomic number (Z)	87
Group	group 1 (alkali metals)
Period	period 7
Block	s-block
Element category	alkali metal
Electron configuration	[Rn] 7s1
Electrons per shell	2, 8, 18, 32, 18, 8, 1
Physical properties
Phase at STP	Fr: Solid
Melting point	300 K ​(27 °C, ​81 °F)
Boiling point	950 K ​(677 °C, ​1251 °F)
Density (near r.t.)	2.48 g/cm3 (estimated)
Vapor pressure (extrapolated) P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 404 454 519 608 738 946
Atomic properties
Oxidation states	+1 (a strongly basic oxide)
Electronegativity	Pauling scale: >0.79
Ionization energies	1st: 393 kJ/mol
Covalent radius	260 pm (extrapolated)
Van der Waals radius	348 pm (extrapolated)
Other properties
Natural occurrence	Fr: From decay
Crystal structure	​body-centered cubic (bcc) (extrapolated)
Thermal conductivity	15 W/(m·K) (extrapolated)
Electrical resistivity	3 µΩ·m (calculated)
Magnetic ordering	Paramagnetic
CAS Number	7440-73-5
History
Naming	after France, homeland of the discoverer
Discovery and first isolation	Marguerite Perey (1939)
Main isotopes of francium
Iso­tope Abun­dance Half-life (1/2) Decay mode Pro­duct 212Fr syn 20.0 min β+ 212Rn α 208At 221Fr trace 4.8 min α 217At 222Fr syn 14.2 min β− 222Ra 223Fr trace 22.00 min β− 223Ra α 219At
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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.