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96 Cm (247)

Curium

Actinoid
Symbol Cm
Atomic Number 96
Atomic Weight (247)
CAS Registry ID 7440-51-9
Group Name Actinoid
Period Number 7
Block f-block
State at STP Solid

Description

Sample of Curium ⌕ Enlarge Image

Curium is a synthetic element that is in the family of actinides. When it is synthesized, it is solid with a silvery color. Curium has an atomic weight of 247, a melting point of 2444 °F, and a boiling point of 5630 °F. Currently this element has no commercial uses. It is being studied as a possible future fuel source for radioisotope thermoelectric generators. It is highly toxic and must be handled with great care.

Isolation

Curium does not exist in nature and can only be synthesized artificially using very specialized equipment. Once it is synthesized it is only used for scientific tests.

Curium ⌕ Enlarge Image

Curium is synthesized by bombarding plutonium with alpha particles. The alpha particles are formed from two protons and two neutrons that are identical to the nucleus of the element helium. The particles are gathered by emissions from uranium or radium through alpha decay. Most alpha particles have a high amount of energy; they are dangerous in that they can be absorbed by human skin and tissue. In 1944 curium was first synthesized by bombarding the alpha particles onto the isotope, number 239, of plutonium. The experiment was carried out in a cyclotron; a cyclotron is a particle accelerator which works though high frequencies and alternating voltage. The hydroxide form of the isotope, number 242, of curium was synthesized by bombarding the isotope, number 241, of americium with neutrons. Isolated isotopes of curium do develop high amounts of gamma and beta radiation as they decay; this fact has reduced some of the interest in commercial uses of curium.

General

NameCurium
SymbolCm
Number96
Chemical seriesActinoid
Groupn/a
Period7
Blockf
Appearancesilvery
Standard atomic weight(247) g·mol⁻¹
Electron configuration[Rn] 5f7 6d1 7s2
Electrons per shell2, 8, 18, 32, 25, 9, 2

Atomic Properties

Crystal structurehexagonal close-packed
Oxidation states3 (amphoteric oxide)
Electronegativity1.3 (scale Pauling)
Ionization energies1st: 581 kJ/mol
Atomic radius
Atomic radius (calc.)
Covalent radius
Van der Waals radius

Physical Properties

Phasesolid
Density (near r.t.)13.51  g·cm−3
Liquid density at m.p.
Melting point1613 K (1340 °C, 2444 °F)
Boiling point3383 K (3110 °C, 5630 °F)
Critical point
Heat of fusion15  kJ·mol−1
Heat of vaporization
Heat capacity

Miscellaneous

Magnetic ordering
Electrical resistivity
Thermal conductivity
Thermal expansion
Speed of sound (thin rod)
Young's modulus
Shear modulus
Bulk modulus
Poisson ratio
Mohs hardness
Vickers hardness
Brinell hardness