ElementsWhat is americium?
Americium is a radioactive, silvery metal made in nuclear reactors.
What is americium used for?
A tiny amount is used in many household smoke detectors. Also industrial gauges.
Where the name comes from
From the Americas, by analogy with europium.
Key facts
- Symbol
- Am
- Atomic number
- 95
- Atomic mass
- 243.061380 u
- Family
- Actinide
- Period
- 7
- Group
- none (f-block)
- Block
- f
- State at room temperature
- Solid
- Melting point
- 1,176 °C (1,449 K, 2,149 °F)
- Boiling point
- 2,011 °C (2,284 K, 3,652 °F)
- Density
- 13.69 g/cm³
- Electrons per shell
- 2, 8, 18, 32, 25, 8, 2
- Electron configuration
- [Rn]7s2 5f7
- Common oxidation states
- +6, +5, +4, +3
- Electronegativity (Pauling)
- 1.3
- First ionisation energy
- 5.993 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 244 pm
- Discovered
- 1944
Place in the periodic table
Americium is element number 95. It sits in period 7 (row 7) of the periodic table, in the separate row of actinides drawn below the main table, and belongs to the f-block. Just before it comes plutonium (94), and just after it comes curium (96).
Family: Actinides.
Physical properties
At room temperature americium is a solid. It melts at 1,176 °C and boils at 2,011 °C, so it stays liquid over a range of 835 degrees. Its density is 13.69 grams per cubic centimetre, so a one-litre block would weigh about 13.69 kilograms. By density it ranks 13th among the 96 elements with a measured value.
Inside the atom
An atom of americium has 95 protons in its nucleus and, when neutral, 95 electrons around it. The electrons are arranged in 7 shells: 2, 8, 18, 32, 25, 8, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Rn]7s2 5f7.
Its electronegativity on the Pauling scale is 1.3. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 5.993 electronvolts (about 578 kilojoules per mole). One mole of americium weighs 243.061380 grams, so a single gram contains about 2.48 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains americium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.