96 Cm (247)

Curium

Actinide Curium solid Radioactivity

[Rn] 5f⁷ 6d¹ 7s² · 2 · 8 · 18 · 32 · 25 · 9 · 2

← Am Americium Bk Berkelium →

An actinide named for the Curies. Curium emits alpha particles so intensely that a solution of its salts heats itself and glows pale violet in the dark.

3D model

Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.

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Atomic properties

Atomic number: 96
Atomic mass: 247 а.е.м. ≈
Electron configuration: [Rn] 5f⁷ 6d¹ 7s²
Electrons per shell: 2 · 8 · 18 · 32 · 25 · 9 · 2
Block: f-block
Group: no data
Period: 7
Electronegativity (Pauling): 1.28
Electronegativity (Allen): 1.28
Atomic radius: 245 pm
Covalent radius: 169 pm
Van der Waals radius: 245 pm
Ionisation energy 1: 581 kJ/mol
Electron affinity: 27.2 kJ/mol
Common oxidation states: +3
Oxidation states: +3, +4, +5, +6, +8

Physical properties

State at 25 °C: solid
Density: 13.51 g/cm³
Melting point: 1 613 K · 1 339.9 °C
Boiling point: 3 383 K · 3 109.9 °C ≈
Speed of sound: no data

Thermal properties

Heat of fusion: 15 kJ/mol
Heat of vaporisation: 320 kJ/mol ≈
Specific heat capacity: 0.08 J/(g·K)
Thermal conductivity: 8.8 W/(m·K)

Mechanical properties

Young's modulus: no data
Shear modulus: no data
Bulk modulus: no data
Poisson ratio: no data
Mohs hardness: no data
Brinell hardness: no data

Electrical and magnetic properties

Electrical resistivity: 1 250 nΩ·m
Magnetic ordering: antiferromagnetic
Curie point: no data
Néel point: 65 K
Superconducting point: no data

Crystal structure

Crystal structure: hexagonal close-packed (hcp)
Lattice constants: a = 349.6 pm · c = 1 133.1 pm

Abundance

In the crust: does not occur
In the ocean: does not occur
In the universe: does not occur
In the human body: does not occur

Isotopes

Isotope	Abundance	Half-life	Decay mode
²⁴⁴Cm	—	18.09 yr	α
²⁴⁷Cm	—	15.6 Myr	α
²⁴⁸Cm	—	347 942.35 yr	α

Curium-244, half-life 18 years, gives about 3 W of heat per gram. Curium-247, half-life 15.6 million years, is the longest-lived isotope.

Discovery

Year of discovery: 1944
Discovered by: Seaborg, James and Ghiorso
Where: Berkeley, USA
Origin of the name: after Marie and Pierre Curie

History

Seaborg, James and Ghiorso synthesised curium in the summer of 1944 at Berkeley by bombarding plutonium with alpha particles. Paradoxically curium was made before americium, despite its higher number.

Where it occurs

Absent from nature.

How it is produced

In reactors by repeated neutron capture. Curium-244 accumulates in spent fuel and contributes noticeably to its heat output after decades of storage.

Role in living things

No biological role.

Safety

Extremely radiotoxic and bone-seeking. It is handled in hot cells.

Uses

Alpha spectrometers for soil analysis: the APXS instruments on Mars rovers run on curium-244
Neutron and power sources in spacecraft
Breeding heavier actinides under reactor irradiation

Curiosities

The APXS spectrometers on Sojourner, Spirit, Opportunity and Curiosity all measured Martian rock composition using curium-244.
Curium solutions glow in the dark from their own radioluminescence.
Curium was synthesised before americium, despite following it in the table.
Curium is the only element named after a married couple.