Curium (Cm)

Every Mars rover from Sojourner to Curiosity has carried curium: its alpha-particle X-ray spectrometer uses curium-244 to bombard a rock and read back the elements from the X-rays that come off, an instrument that needs no power beyond the isotope itself. Curium glows purple in the dark from its own radioactivity. Seaborg's group nicknamed it and americium "pandemonium" and "delirium" during the war years, when both were classified and neither could be written about.

Properties

Atomic number

96

Symbol

Cm

Mass number of most stable isotope

[247]

Category

Actinide

Period

7

Block

f-block

Electron configuration

[Rn] 7s² 5f⁷ 6d¹

Electrons per shell

2, 8, 18, 32, 25, 9, 2

Melting point

1,618 K — 1344.8 °C — 2452.7 °F

Boiling point

3,400 K — 3126.8 °C — 5660.3 °F

Density

13.51 g/cm³

Electronegativity

1.3 (Pauling)

Oxidation states

+3

Discovered

1944 by Glenn Seaborg, Ralph James and Albert Ghiorso

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁷ 6d¹

Noble gas shorthand

[Rn] 7s² 5f⁷ 6d¹

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 25 · P: 9 · Q: 2

What it is used for

• Alpha-particle X-ray spectrometers on Mars rovers, for analysing rocks
• A starting material for making heavier elements in accelerators
• Research into transmuting long-lived nuclear waste

Hazards

• Intensely radioactive; curium-244 puts out about 3 watts of heat per gram

Anomalous electron configuration: [Rn] 7s² 5f⁷ 6d¹ rather than the predicted 7s² 5f⁸ — the half-filled f subshell effect, exactly as in gadolinium directly above it. No stable isotope; the mass given is the mass number of curium-247, the longest-lived at 15.6 million years.

Neighbours in the table