Curium

Named for Marie and Pierre Curie, and used to read the chemistry of rocks on Mars.

At a glance

Symbol: Cm
Atomic number: 96
Mass number of its longest-lived isotope: [247]
Group: none; it sits in the actinide row below the table
Period: 7
Family: actinide
Electron configuration: [Rn] 5f⁷ 6d¹ 7s²
Electronegativity: 1.30
Common ions: Cm³⁺
Isotopes: none are stable; ²⁴⁷Cm lasts longest, about 16 million years; ²⁴⁴Cm is the most used

On the table

Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.

Electrons and bonding

Radioactive, like every actinide. It gives up electrons to form positive ions.

Properties

State at 25 °C: solid
What it looks like: hard, silvery, radioactive metal
Melting point: 1345 °C
Boiling point: 3127 °C
Density: 13.5 g/cm³

Where it is found

Not found in nature. It forms in nuclear reactors from plutonium and americium.

Discovery and name

Glenn Seaborg, Ralph James and Albert Ghiorso made it in 1944 in Chicago by bombarding plutonium-239 with alpha particles, a few months before americium. It was named after Marie and Pierre Curie, just as gadolinium above it honors Johan Gadolin.

What it is used for

Curium-244 is the radiation source in the X-ray spectrometers that Mars rovers from Sojourner to Curiosity used to identify the elements in rocks. It is also used to make heavier elements for research.

In compounds

CmO₂curium dioxideCm₂O₃curium(III) oxide

Handle with care

Intensely radioactive, and stored in bone and the liver if taken into the body.