About

Americium is a synthetic radioactive element with a silvery luster, named after the Americas. Its most common and well-known application is in household ionization-type smoke detectors. A tiny amount of americium-241 emits alpha particles that ionize the air in a chamber; smoke disrupts this current, triggering the alarm. It is also used in some industrial gauges.

Atomic Properties

Atomic Number95

Atomic Weight243.061 u

Neutrons (common)148

Electron Configuration[Rn] 5f⁷ 7s²

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 5f⁷ 7s²

Electrons per Shell2, 8, 18, 32, 25, 8, 2

Electronegativity1.13

Electron Affinity9.93 kJ/mol

Oxidation States+6, +5, +4, +3

Covalent Radius180 pm

Ionic Radius97.5 pm

Periodic Table Position

Group3

Period7

BlockF

Chemical SeriesActinoids

Physical Properties

State at STPsolid

Appearancesilvery white radioactive metal

Crystal Structurehcp

Magnetic Orderingparamagnetic

Thermal Properties

Melting Point1,449 K

Boiling Point2,880 K

Thermal Expansion0 1/K

Thermal Conductivity10 W/(m·K)

Specific Heat0.11 J/(g·K)

Molar Heat26.74 J/(mol·K)

Heat of Fusion14.39 kJ/mol

Heat of Vaporization238.5 kJ/mol

Discovery

Discovered byGlenn T. Seaborg, Ralph A. James, Leon O. Morgan, Albert Ghiorso

Discovery Year1,944

Occurrencesynthetic

CAS Number7440-35-9

Electron Configuration

Energy

↿⇂

1s

↿⇂

2s

↿⇂

2p

↿⇂

3s

↿⇂

3p

↿⇂

4s

↿⇂

3d

↿⇂

4p

↿⇂

5s

↿⇂

4d

↿⇂

5p

↿⇂

6s

↿⇂

4f

↿⇂

5d

↿⇂

6p

↿⇂

7s

↿

5f

6d

7p

Isotopes of Americium

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
²⁴¹Am	241.056820	—	432.6 y	Alpha Decay
²⁴³Am	243.061380	—	7.350 ky	Alpha Decay