Actinium Ac (Element 89) of Periodic Table

89 Ac (Actinium)

Appearance:  Soft, Silvery-white, glows in the dark with a pale blue light because intense radioactivity exicites the air around it; sometimes with a golden cast

Mass number:  227

Atomic weight:  227.0278 g/mol

Atomic number(Z):  89

Electrons:  89

Protons:  89

Neutrons:  138

Group:  3

Period:  7

Block:  d

Element category:  Actinide

Electrons per shell:  K2, L8, M18, N32, O18, P9, Q2

Electron configuration: 1s22s22p63s23p63d104s24p64d105s25p64f145d106s26p66d17s2

Phase:  Solid

Melting point:  1500 K(1227 oC)

Boiling point:  3500±300 K (3227±300 oC)

Density:  10 g/cm3

Molar volume:  0.000022542 m3/mol

Thermal conductivity:  12 W/m∙K

Half Life(s):  687060000

Lifetime(s):  991210000

Decay mode:  β decay

Neutron cross section (Barns): 810

Heat of fusion: 14 kJ/mol

Heat of vaporization:  400 kJ/mol

Molar heat capacity:  27.2 J/(mol∙K)

Oxidation states:  3, 2

Ion charge:  Ac4+

Electronegativity:  1.1

Valence:  3

Ionization energies:  1st: 499 kJ/mol  2nd:  1170 kJ/mol  3rd:  1900 kJ/mol

Covalent radius:  215 pm

Crystal structure:  Face centered cubic

Thermal conductivity:  12 W/(m∙K)

CAS Number:  7440-34-8

Discovery & 1st isolation:  Friedrich Oskar Giesel (1902)

Named:  After Greek word ‘Actinos’ (means a ray) by André-Louis Debierne (1899)

Isotopes: 225Ac 226Ac 227Ac

Uses:  Actinium is a very powerful source of α rays, but is rarely used outside research.

Biological role:  It is toxic due to its radioactivity.

Natural abundance:  Actinium is made by the neutron bombardment of radium-226. It is also occurs naturally in uranium ores


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