Francium

87

Fr

(223)

  • Name: Francium
  • Symbol: Fr
  • Atomic number: 87
  • Atomic weight: (223)
  • CAS Registry ID: 7440-73-5
  • Group name: Alkali metal
  • Period number: 7
  • Block: s-block
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Description

Francium is a highly radioactive element that has the lowest electronegativity of all the elements. This element is so radioactive that not much is really known about it. It is classified as an alkali metal, but no one knows whether it is a solid or liquid. The melting point is estimated at 80 ° F, and the boiling point is not yet known or even approximated. Francium has an atomic weight of 223 and is one of the rarest elements on Earth second only to astatine.

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Isolation

Francium is a naturally occurring element that quickly decays into astatine, radium, and radon. Its decay rate is so quick that it has not yet been isolated.

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Trace amounts of francium have been found in uranium and thorium mineral ores. In these ores, the francium element is present in an isotope form, number 223. Isolation has so far proved unsuccessful as any element that is formed immediately decays again; it has a half life of only 22 minutes. Francium has been successfully synthesized, but this too is an extremely complicated procedure and only very minute amounts can be synthesized. A nuclear reaction involving an isotope of gold and oxygen will produce francium isotopes; the isotopes are then isolated using a magneto-optic trap. Radium bombardment with neutrons and thorium protons can also synthesize francium. Francium that has been created has been held as an ultra-cold gas; in this state the atoms of the element were close to absolute zero. The very tiny amounts of francium that have been synthesized have been so small that no measurements of the weight could be obtained.


General
Name Francium
Symbol Fr
Number 87
Chemical series alkali metals
Group 1
Period 7
Block s
Appearance metallic
Standard atomic weight (223)  g·mol−1
Electron configuration [Rn] 7s1
Electrons per shell 2, 8, 18, 32, 18, 8, 1
Atomic properties
Crystal structure cubic body centered
Oxidation states 1 (strongly basic oxide)
Electronegativity 0.7 (scale Pauling)
Ionization energies 1st: 380 kJ/mol
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Atomic radius
Atomic radius (calc.)
Covalent radius
Van der Waals radius
Physical properties
Phase solid
Density (near r.t.) 1.87  g·cm−3
Liquid density at m.p.
Melting point 300 K (27 °C, 80 °F)
Boiling point 950 K (677 °C, ? 1250 °F)
Critical point
Heat of fusion ca. 2  kJ·mol−1
Heat of vaporization ca. 65  kJ·mol−1
Heat capacity
Miscellaneous
Magnetic ordering
Electrical resistivity 3 µΩ·m
Thermal conductivity (300 K) ? 15  W·m−1·K−1
Thermal expansion
Speed of sound (thin rod)
Young's modulus
Shear modulus
Bulk modulus
Poisson ratio
Mohs hardness
Vickers hardness
Brinell hardness
CAS registry number 7440-73-5

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