Curium
Actinide · Period 7 · f-block
Named for the Curies, it analyses rocks on Mars and comets
- Atomic mass
- 247 u
- State at 25 °C
- Solid
- Electronegativity
- 1.28
- Melting point
- 1,339.9 °C
- Boiling point
- 3,109.9 °C
- Configuration
- [Rn] 5f7 6d1 7s2
Nucleus drawn at reduced count for clarity. Drag to rotate.
Curium, explained
Video lesson in production
Bhavya’s explainer for this element will play here.
Overview
Curium is a hard, dense, silvery actinide metal with the configuration 5f7 6d1 7s2. When it loses three electrons, it is left with exactly seven 5f electrons, a half-filled shell that is especially stable. As a result, curium almost always appears as Cm3+, and it closely parallels gadolinium, the lanthanide directly above it with a half-filled 4f7 shell. Like gadolinium, curium metal is magnetic at low temperatures, ordering antiferromagnetically below about 52 K.
Curium's isotopes are all radioactive and many release a great deal of heat. Curium-242 produces about 120 watts per gram, and curium-244, with an 18-year half-life, is a steady alpha emitter. That steady alpha output makes curium-244 ideal for alpha particle X-ray spectrometers on planetary missions, which bombard rock with alpha particles and X-rays and read the elements present from what bounces back. The longest-lived isotope, curium-247, has a half-life of 15.6 million years.
Discovery
Glenn Seaborg, Ralph James and Albert Ghiorso made curium in July 1944 by bombarding plutonium-239 with alpha particles in the Berkeley 60-inch cyclotron, then identified it chemically at the Metallurgical Laboratory in Chicago. It was named after Marie and Pierre Curie, in parallel with gadolinium, named after the chemist Johan Gadolin. Its discovery stayed secret until Seaborg mentioned it on the radio in November 1945.
- Where it’s found
- Curium does not occur naturally in useful amounts; it is produced in nuclear reactors by repeated neutron capture in plutonium and americium, and recovered from spent fuel.
- What it’s used for
- Planetary X-ray spectrometers
- Targets for superheavy elements
- Production of heavier actinides
- Space power research
- In living things
- Curium has no biological role; absorbed curium accumulates in bone, liver and lungs, where its alpha radiation causes cancer.
- Safety
- Intensely radioactive and heat-producing; handled only in hot cells and glove boxes. It is mainly dangerous if inhaled or ingested.
How it compares
Where Curium sits among all 118 elements on the trends that shape the table.
- Electronegativity1.28Pauling
#71 of 100 elements with data
- Ionization energy581kJ/mol
#76 of 104 elements with data
- Atomic radius176pm
#24 of 95 elements with data
- Electron affinity27.2kJ/mol
#73 of 109 elements with data
- Density13.5g/cm³
#26 of 114 elements with data
- Melting point1,610K
#37 of 110 elements with data
- Density
- 13.5 g/cm³
- Atomic radius
- 176 pm
- Covalent radius
- 166 pm
- Molar heat
- —
- Appearance
- silvery metallic, glows purple in the dark
- Discovered by
- Glenn T. Seaborg
Inside the atom
96 electrons arranged in 7 shells: 2 · 8 · 18 · 32 · 25 · 9 · 2.
Orbital diagram
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f7 6d1 · shorthand [Rn] 5f7 6d1 7s2
- 1s2
- 2s2
- 2p6
- 3s2
- 3p6
- 4s2
- 3d10
- 4p6
- 5s2
- 4d10
- 5p6
- 6s2
- 4f14
- 5d10
- 6p6
- 7s2
- 5f7
- 6d1
Each box is an orbital holding up to two electrons of opposite spin. Highlighted subshells hold the valence electrons that decide how Curium bonds.
Signature reactions
The chemistry Curium is known for.
Nuclear · Alpha bombardment
Discovery of curium
Plutonium-239 absorbs an alpha particle and ejects one neutron, forming curium-242. The new isotope was identified by its characteristic alpha radiation after chemical separation.
Conditions: 32 MeV alpha particles from a cyclotron
Nuclear · Alpha decay
Alpha decay of curium-244
Curium-244 emits a 5.8 MeV alpha particle and becomes plutonium-240. Planetary spectrometers use these alpha particles to probe the composition of rocks and soil.
Conditions: spontaneous; half-life 18.1 years
Precipitation
Precipitating curium(III) fluoride
Curium(III) fluoride is insoluble, like the fluorides of the lanthanides. Fluoride precipitation helped chemists separate trace curium from other elements in early experiments.
Conditions: aqueous acid solution
Where you’ll meet it
Alpha particle X-ray spectrometer
Alpha particle X-ray spectrometers on Mars rovers use curium-244 to identify the elements in rocks.
Photo: Wikimedia Commons
Sojourner rover
In 1997 the Sojourner rover carried a curium-powered spectrometer to Mars.
Photo: Wikimedia Commons
Philae lander
The Philae lander analysed a comet's surface in 2014 with a curium-244 spectrometer.
Photo: Wikimedia Commons
Marie Curie
Curium honours Marie and Pierre Curie, pioneers of radioactivity research.
Photo: Wikimedia Commons
.png){kind=link}
Research
No research on Curium yet
When Bhavya publishes a project that studies Curium, it will be linked here.