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89Ac227.000
Actinium
ActinideActinium is a radioactive chemical element with symbol Ac (not to be confused with the abbreviation for an acetyl group) and atomic number 89, which was discovered in 1899. It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902.
Phase: Solid
2, 8, 18, 32, 18, 9, 2
Physical Properties
Atomic Mass227 u
Density10 g/cm³
Melting Point1500 K
Boiling Point3500 K
Molar Heat27.2 J/(mol·K)
Period7
PhaseSolid
Chemical Properties
Electron Configuration1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 6d1
Semantic Config[Rn] 6d1 7s2
Shells2, 8, 18, 32, 18, 9, 2
Electron Affinity33.77 kJ/mol
Electronegativity1.1
Ionization Energies
IE1: 499 kJ/molIE2: 1170 kJ/mol
Discovery
Discovered byFriedrich Oskar Giesel