Curium (Cm)

Curium properties

Atomic number

96

Atomic mass

247 u

Category

Actinide

Group

—

Period

7

Block

f-block

State at room temp.

Solid

Electronegativity

1.3

Melting point

1,613 K (1,339.8 °C)

Boiling point

3,383 K (3,109.8 °C)

Density

13.51 g/cm³

Valence electrons

2

Common charges

+3

Oxidation states

+3

Atomic radius

245 pm

Ionization energy

6.02 eV

Electron affinity

—

Radioactive

Yes, no stable isotopes

Discovered

1944

Curium electron configuration

The electron configuration of Curium (Cm) is [Rn] 5f7 6d1 7s2. Its 96 electrons are arranged in shells as 2, 8, 18, 32, 25, 9, 2.

Protons, neutrons and electrons in Curium

A neutral Curium atom has 96 protons and 96 electrons. Most Curium atoms have about 151 neutrons: the atomic mass rounded to 247, minus the atomic number 96.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Curium have?

2

Curium has 2 valence electrons in its outermost shell. As an f-block element, its 4f or 5f electrons can also take part in bonding.

See every element: Periodic table with valence electrons

Curium orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Curium

247 g/mol

One mole of Curium atoms (6.022 × 10²³ atoms) has a mass of 247 grams. Use this value to convert between grams and moles.

Curium facts

• Curium was named after the Curies by analogy with gadolinium, the element above it, which honors chemist Johan Gadolin.
• Its longest-lived isotope, curium-247, has a half-life of about 15.6 million years.
• Curium (Cm) has atomic number 96 and is a solid at room temperature. It was discovered in 1944.

Position in the periodic table

Curium is element 96, in period 7 of the periodic table. It is one of the Actinides in the f-block, shown in the rows below the main table.

All actinides

Uses of Curium

Curium is used mainly in research and as a compact radiation source. Curium-244 is the alpha source in the alpha particle X-ray spectrometers carried by Mars rovers, including Sojourner, Spirit, Opportunity and Curiosity, which measure the chemical makeup of rocks. Curium targets are also used to make heavier elements, including livermorium.

Who discovered Curium?

Glenn Seaborg, Ralph James and Albert Ghiorso first made curium in 1944 by bombarding plutonium with alpha particles in a cyclotron at Berkeley, and identified it at the University of Chicago. It was named after Marie and Pierre Curie.

Where does the name come from?

Curium honors Marie and Pierre Curie, pioneers in the study of radioactivity. The name follows the example of gadolinium, the element above it in the periodic table, which was named in honor of the chemist Johan Gadolin.

Discovery timeline