Curium (Cm)
“Named for the Curies and flown to Mars — curium interrogates red-planet rocks aboard rovers from Sojourner to Curiosity.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- Fiercely radioactive: Cm-242 (half-life 163 days) and Cm-244 (18 years) are both alpha powerhouses, and concentrated samples literally keep themselves warm.
- Its true configuration is [Rn] 5f⁷ 6d¹ 7s² — an aufbau exception that keeps the 5f subshell exactly half-filled for extra stability.
- Chemistry is classic actinide: the +3 state dominates, with +4 appearing in solid compounds such as curium dioxide (CmO₂).
- Produced in gram quantities by neutron bombardment of plutonium or americium in research reactors — among transuranics only americium is more routinely available.
A hard, lustrous, silvery metal — yet almost never seen, because curium is so intensely radioactive that a concentrated sample warms itself and can glow from its own decay energy. Chemists usually meet it as a few micrograms sealed inside a glovebox.
Where you meet it
✦ Uses
- Alpha-particle X-ray spectrometers (APXS) on Mars rovers: a Cm-244 source fires alpha particles at rocks, and the X-rays knocked back out reveal their chemical make-up — the trick behind the rock reports of Sojourner, Spirit, Opportunity and Curiosity.
- The Philae lander’s APXS carried curium to comet 67P/Churyumov–Gerasimenko in 2014, remotely tasting the comet’s surface dust.
- Curium-248 targets for superheavy-element factories: fusing them with calcium-48 beams created livermorium, element 116, at Dubna.
- Studied as a compact radioisotope heat source because its alpha decay runs hot — although spacecraft still mostly fly plutonium-238.
◍ Everyday examples
- When Curiosity beams home the chemistry of a Martian mudstone, every headline traces back to a fingertip-sized curium source doing the asking.
- Physics textbooks measure radioactivity in the old unit called the curie; the chemistry chapter returns the favour with element 96 — a double tribute to one scientist.
History & name
In mid-1944 Glenn Seaborg, Ralph James and Albert Ghiorso, again at Chicago’s Metallurgical Laboratory, bombarded plutonium-239 with alpha particles in Berkeley’s 60-inch cyclotron, forging curium-242. The new atoms were masked by their own ferocious radioactivity, so the chemical proof was only completed in early 1945 — americium, discovered months later, was actually announced first. Curium went public together with americium in late 1945, named after Marie and Pierre Curie, discoverers of radium and polonium. The naming deliberately mirrored gadolinium: the lanthanide sitting directly above curium honours Johan Gadolin, just as element 96 honours radioactivity’s first family.