Francium

Francium, ₈₇Fr

Francium
Pronunciation	/ˈfrænsiəm/ ​(FRAN-see-əm)
Mass number	[223]
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: hydrogen and alkali metals
Period	period 7
Block	s-block
Electron configuration	[Rn] 7s1
Electrons per shell	2, 8, 18, 32, 18, 8, 1
Physical properties
Phase at STP	solid
Melting point	300 K ​(27 °C, ​81 °F)
Boiling point	950 K ​(677 °C, ​1251 °F)
Density (near r.t.)	2.458 g/cm3 (estimated)[1]
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 (expected to have a strongly basic oxide)
Electronegativity	Pauling scale: >0.79
Ionization energies	1st: 393 kJ/mol[2]
Covalent radius	260 pm (extrapolated)
Van der Waals radius	348 pm (extrapolated)
Other properties
Natural occurrence	from decay
Crystal structure	​body-centered cubic (bcc) (extrapolated)[1]
Lattice constant	a = 670.4 pm (estimated)[1]
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)
Isotopes of francium v e
Main isotopes[3] Decay abun­dance half-life (t1/2) mode pro­duct 212Fr synth 20.0 min β+ 212Rn α 208At 221Fr trace 4.8 min α 217At 222Fr synth 14.2 min β− 222Ra 223Fr trace 22.00 min β− 223Ra α 219At
Category: Francium view talk edit | references

Francium is a chemical element; it has symbol Fr and atomic number 87. It is extremely radioactive; its most stable isotope, francium-223 (originally called actinium K after the natural decay chain in which it appears), has a half-life of only 22 minutes.^[4] It is the second-most electropositive element, behind only caesium, and is the second rarest naturally occurring element (after astatine). Francium's isotopes decay quickly into astatine, radium, and radon. The electronic structure of a francium atom is [Rn] 7s¹; thus, the element is classed as an alkali metal.

Bulk francium has never been seen. Because of the general appearance of the other elements in its periodic table column, it is presumed that francium would appear as a highly reactive metal if enough could be collected together to be viewed as a bulk solid or liquid. Obtaining such a sample is highly improbable since the extreme heat of decay resulting from its short half-life would immediately vaporize any viewable quantity of the element.

Francium was discovered by Marguerite Perey^[5] in France (from which the element takes its name) in 1939.^[6] Before its discovery, francium was referred to as eka-caesium or ekacaesium because of its conjectured existence below caesium in the periodic table. It was the last element first discovered in nature, rather than by synthesis.^{[note 1]} Outside the laboratory, francium is extremely rare, with trace amounts found in uranium ores, where the isotope francium-223 (in the family of uranium-235) continually forms and decays. As little as 1 ounce (28 g) exists at any given time throughout the Earth's crust; aside from francium-223 and francium-221, its other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.^[7]

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