Americium (Am)

Americium properties

Atomic number

95

Atomic mass

243 u

Category

Actinide

Group

—

Period

7

Block

f-block

State at room temp.

Solid

Electronegativity

1.3

Melting point

1,449 K (1,175.8 °C)

Boiling point

2,880 K (2,606.8 °C)

Density

12 g/cm³

Valence electrons

2

Common charges

+3, +4, +5, +6

Oxidation states

+6, +5, +4, +3

Atomic radius

244 pm

Ionization energy

5.993 eV

Electron affinity

—

Radioactive

Yes, no stable isotopes

Discovered

1944

Americium electron configuration

The electron configuration of Americium (Am) is [Rn] 5f7 7s2. Its 95 electrons are arranged in shells as 2, 8, 18, 32, 25, 8, 2.

Protons, neutrons and electrons in Americium

A neutral Americium atom has 95 protons and 95 electrons. Most Americium atoms have about 148 neutrons: the atomic mass rounded to 243, minus the atomic number 95.

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

How many valence electrons does Americium have?

2

Americium 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

Americium 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 Americium

243 g/mol

One mole of Americium atoms (6.022 × 10²³ atoms) has a mass of 243 grams. Use this value to convert between grams and moles.

Americium facts

• Glenn Seaborg first revealed americium and curium to the public on a children's radio quiz show in November 1945.
• Americium-241 has a half-life of about 432 years.
• Americium (Am) has atomic number 95 and is a solid at room temperature. It was discovered in 1944.

Position in the periodic table

Americium is element 95, 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 Americium

Americium-241 is found in many household smoke detectors, where a tiny amount ionizes the air inside a small chamber; smoke particles disrupt the resulting electric current and trigger the alarm. The same isotope is used in industrial gauges that measure the thickness of materials and, combined with beryllium, as a neutron source for exploring oil wells.

Who discovered Americium?

Glenn Seaborg, Ralph James, Leon Morgan and Albert Ghiorso first made americium in 1944 at the wartime Metallurgical Laboratory of the University of Chicago. It was named after the Americas, just as europium, the element above it, is named after Europe.

Where does the name come from?

Americium is named after the Americas, where it was first made in 1944. Its discoverers chose the name by analogy with europium, the element directly above it in the periodic table, which is named after Europe.

Discovery timeline