095Actinide · Group 3 · Period 7

Americium

Americium (Am) is element 95, a actinide in the f-block — group 3, period 7. It is a solid at room temperature with 7 electron shells (2, 8, 18, 32, 25, 8, 2) and an atomic mass of 243 u.

Atomic mass: 243.0 u
Phase · STP: solid
Melting: 1449 K · 1176 °C
Boiling: 2880 K · 2607 °C
Electronegativity: 1.13
Density: 12 g/cm³

Photograph — Bionerd, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons

Emission spectrum

The visible light Americium emits when energised — its unique spectral fingerprint.

Identity

Atomic number: 95
Standard atomic weight: 243.0 u
Category: Actinide
Group: 3
Period: 7
Block: f-block
Oxidation states: +6, +5, +4, +3

Physical properties

Melting point: 1449 K · 1176 °C
Boiling point: 2880 K · 2607 °C
Density: 12 g/cm³
Molar heat capacity: 62.7 J/(mol·K)
Atomic radius: 244 pm
Electron affinity: 9.93 kJ/mol

Atomic structure

95protons

148neutrons

95electrons

2valence e⁻

Noble-gas notation: [Rn] 5f7 7s2
Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f7
Electrons per shell: 2, 8, 18, 32, 25, 8, 2

Periodic trends

Where Americium ranks across all 118 elements.

Electronegativity1.13

Ionization energy578 kJ/mol

Electron affinity9.93 kJ/mol

Density12 g/cm³

Atomic radius244 pm

Discovery

Discovered: 1944
Discovered by: Glenn T. Seaborg
Named by: —
Appearance: silvery white