Americium

plutonium ← americium → curium Eu ↑ Am ↓ —

Atomic properties Atomic number 95 Electron configuration [Rn] 5f7 7s2 Physical properties Melting point 876(5) °C (1149(5) K) Boiling point 2067 °C (2340 K) Density 13.671 g cm−3 Electric resistivity 68 × 10−6 Ω cm Chemical properties Electronegativity 1.3 (Pauling) Ionization energies 1st 5.9738(2) eV, 576.38(2) kJ mol−1 2nd 12.5 eV 1206 kJ mol−1 3rd 18.8 eV 1814 kJ mol−1 Atomic radii Covalent radius 180 pm Metallic radius 173 pm Ionic radius 85 pm (Am4+, Oh) 97.5 pm (Am3+, Oh) 121 pm (Am2+, Oh) Thermodynamic properties Standard entropy 55 J K−1 mol−1 Enthalpy change of fusion 14.4 kJ mol−1 Enthalpy change of vaporization 230.2 kJ mol−1 Molar heat capacity (Cp) 25.5 J K−1 mol−1 Miscellaneous CAS number 7440-35-9 EC number 231-144-4 Where appropriate, and unless otherwise stated, data are given for 100 kPa (1 bar) and 298.15 K (25 °C).

Americium (symbol: Am) is a synthetic chemical element, a member of the actinoid series. It is produced in commercial nuclear reactors, although it is not currently extracted during normal fuel reprocessing: nevertheless, kilogram quantities of ²⁴¹Am (t_½ = 432.2(7) a) and ²⁴³Am (t_½ = 7.37(4) × 10³ a) are available from the reprocessing of specialized fuel batches. It has a number of small-scale commercial uses, particularly in domestic smoke alarms.

Americium was first prepared in 1944 in the University of Chicago Metallurgical Laboratory. It was named after the continent of America, by analogy with europium, its lanthanoid homologue, named after the continent of Europe.

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