Francium

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, ₀₀Fr

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
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.)	2.48 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 (expected to have 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	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)
Isotopes of francium
Main isotopes 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

Francium reacts violently with water, as do all of the elements in group 1 on the periodic table.

Francium is one of the hardest to find elements on the planet Earth. It is estimated that there are only about 15 grams or half an ounce in the Earth's crust at a single time.

Although chemists knew the element number 87 in the periodic table should exist, it was a long time before it was discovered. In the early 1900s, nearly all boxes on the periodic table had been filled. Chemists knew that one element had been found to fit into each box. Francium was discovered in 1939 by a French chemist called Marguerite Perey. She named it after her home country, France.

Isotopes

There are 34 known isotopes of francium ranging in atomic mass from 199 to 232. Francium-223 and francium-221 are the only isotopes that occur in nature.

Francium-223 is the most stable isotope, with a half-life of 21.8 minutes. Francium-223 is the fifth product of the actinium decay series as the daughter isotope of actinium-227. Francium-223 then decays into radium-223 by beta decay (1.149 MeV decay energy), with a minor (0.006%) alpha decay path to astatine-219 (5.4 MeV decay energy).

Francium-221 has a half-life of 4.8 minutes. It is the ninth product of the neptunium decay series as a daughter isotope of actinium-225. Francium-221 then decays into astatine-217 by alpha decay (6.457 MeV decay energy).