Californium

Californium, ₉₈Cf

Californium
Pronunciation	/ˌkæləˈfɔːrniəm/ ​(KAL-ə-FOR-nee-əm)
Appearance	silvery
Mass number	[251]
Californium 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 Dy ↑ Cf ↓ (Upb) berkelium ← californium → einsteinium
Atomic number (Z)	98
Group	f-block groups (no number)
Period	period 7
Block	f-block
Electron configuration	[Rn] 5f10 7s2[1]
Electrons per shell	2, 8, 18, 32, 28, 8, 2
Physical properties
Phase at STP	solid
Melting point	1173 K ​(900 °C, ​1652 °F)[2]
Boiling point	1743 K ​(1470 °C, ​2678 °F) (estimation)[3]
Density (near r.t.)	15.1 g/cm3[2]
Atomic properties
Oxidation states	+2, +3, +4, +5[4][5]
Electronegativity	Pauling scale: 1.3[6]
Ionization energies	1st: 608 kJ/mol[7]
Spectral lines of californium
Other properties
Natural occurrence	synthetic
Crystal structure	​double hexagonal close-packed (dhcp)
Mohs hardness	3–4[8]
CAS Number	7440-71-3[2]
History
Naming	after California, where it was discovered
Discovery	Lawrence Berkeley National Laboratory (1950)
Isotopes of californium v e
Main isotopes[9][10] Decay abun­dance half-life (t1/2) mode pro­duct 248Cf synth 333.5 d α100% 244Cm SF<0.01% – 249Cf synth 351 y α100% 245Cm SF≪0.01% – 250Cf synth 13.08 y α99.9% 246Cm SF0.08% – 251Cf synth 898 y α 247Cm 252Cf synth 2.645 y α96.9% 248Cm SF3.09% – 253Cf synth 17.81 d β−99.7% 253Es α0.31% 249Cm 254Cf synth 60.5 d SF99.7% – α0.31% 250Cm
Category: Californium view talk edit | references

Californium is a synthetic chemical element; it has symbol Cf and atomic number 98. It was first synthesized in 1950 at Lawrence Berkeley National Laboratory^[11] (then the University of California Radiation Laboratory) by bombarding curium with alpha particles (helium-4 ions). It is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all elements that have been produced in amounts large enough to see with the naked eye (after einsteinium). It was named after the university and the U.S. state of California.

Two crystalline forms exist at normal pressure: one above and one below 900 °C (1,650 °F). A third form exists at high pressure. Californium slowly tarnishes in air at room temperature. Californium compounds are dominated by the +3 oxidation state. The most stable of californium's twenty known isotopes is californium-251, with a half-life of 898 years. This short half-life means the element is not found in significant quantities in the Earth's crust.^{[a] 252}Cf, with a half-life of about 2.645 years, is the most common isotope used and is produced at Oak Ridge National Laboratory in the United States and Research Institute of Atomic Reactors in Russia.

Californium is one of the few transuranium elements with practical applications. Most of these applications exploit the property of certain isotopes of californium to emit neutrons. For example, californium can be used to help start up nuclear reactors, and it is employed as a source of neutrons when studying materials using neutron diffraction and neutron spectroscopy. It can also be used in nuclear synthesis of higher mass elements; oganesson (element 118) was synthesized by bombarding californium-249 atoms with calcium-48 ions. Users of californium must take into account radiological concerns and the element's ability to disrupt the formation of red blood cells by bioaccumulating in skeletal tissue.

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