Americium

Analytical testing dots

Americium is a synthetic element that has the symbol Am and atomic number 95. A radioactive metallic element, americium is an actinide that was obtained in 1944 by bombarding plutonium with neutrons and was the fourth transuranic element to be discovered. It was named for the Americas, by analogy with europium.

 

General
Name, Symbol, Number americium, Am, 95
Chemical series actinides
Group, Period, Block n/a, 7, f
Appearance silvery white sometimes yellow
Standard atomic weight (243) g·mol-1
Electrons per shell 2, 8, 18, 32, 25, 8, 2
Physical properties
Phase solid
Density (near r.t.) 12 g·cm−3
Melting point 1449K
(1176°C, 2149°F)
Boiling point 2880K
(2607°C, 4725°F)
Heat of fusion 14.39 kJ·mol-1
Heat capacity (25°C) 62.7 J·mol-1·K-1
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 1239 1356        
Atomic properties
Crystal structure hexagonal
Oxidation states 6, 5, 4, 3
(amphoteric oxide)
Electronegativity 1.3 (Pauling scale)
Ionization energies 1st: 578 kJ/mol
Atomic radius 175 pm
Miscellaneous
Magnetic ordering no data
Thermal conductivity (300K) 10 W·m-1·K-1
CAS registry number 7440-35-9

 

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