Curium (Cm)
Element 96 · Actinide · atomic mass [247] u · f-block, period 7
Electron shells: 2, 8, 18, 32, 25, 9, 2
Curium glows purple in the dark from its own radioactivity and generates intense heat. NASA rovers have used it to analyse rocks on Mars.
The Mars rovers identified rock chemistry using curium sources aboard the spacecraft.
- Atomic number
- 96
- Atomic mass
- [247] u
- Electron configuration
- [Rn] 7s² 5f⁷ 6d¹
- Group · period · block
- f-block · 7 · f
- Oxidation states
- +3
- Electronegativity
- 1.3 (Pauling)
- Melting point
- 1,345 °C
- Boiling point
- 3,127 °C
- Density
- 13.51 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery, hard metal
- Discovered
- Glenn T. Seaborg, Ralph James and Albert Ghiorso, 1944
96 protons, and 96 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Shown in the strip below the table
What Curium is used for
- Alpha-particle X-ray spectrometers on Mars rovers
- Radioisotope power research
- Producing heavier elements
Atomic structure of Curium
A neutral curium atom has 96 protons and 96 electrons. Its most common isotope carries about 151 neutrons, which is where the mass number 247 comes from. Change the neutron count and you have a different isotope of curium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 25, 9, 2. In orbital notation that is [Rn] 7s² 5f⁷ 6d¹. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Curium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Curium sits in the periodic table
Discovery and naming
Curium was discovered by Glenn T. Seaborg, Ralph James and Albert Ghiorso in 1944. Its name comes from Marie and Pierre Curie, which is also why its symbol (Cm) does not match its English name.
Every isotope of curium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Curium?
Curium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 247 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Curium have?
Curium has 96 protons, because the atomic number is the proton count and that is what makes an atom Curium at all. A neutral Curium atom has the same number of electrons, 96. The neutron count varies by isotope; the most common one has about 151, since 247 − 96 = 151.
What is the electron configuration of Curium?
The electron configuration of Curium is [Rn] 7s² 5f⁷ 6d¹. Its electrons are arranged 2, 8, 18, 32, 25, 9, 2 across 7 shells.
Is Curium a metal?
Yes. Curium is classified as a actinide, on the metallic side of the table.
What group and period is Curium in?
Curium sits in the f-block strip below the main table, in period 7, among the actinides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Curium?
Curium most commonly forms a 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Curium?
Curium melts at 1,345 °C and boils at 3,127 °C. That puts it in the solids at everyday temperatures.
What is Curium used for?
Alpha-particle X-ray spectrometers on Mars rovers, Radioisotope power research, Producing heavier elements. Curium glows purple in the dark from its own radioactivity and generates intense heat.
Who discovered Curium, and where does its name come from?
Curium (Cm) was discovered by Glenn T. Seaborg, Ralph James and Albert Ghiorso in 1944. The name comes from Marie and Pierre Curie.
Is Curium radioactive?
Yes. Every isotope of Curium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.