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Element 91 - Proactinium (Pa) sound

From protos, or first; it is the parent of actinium, which is formed by its radioactive decay; discovered 1917. Third rarest of the elements, it can be prepared by modern chemical techniques from thorium or uranium.

Properties

Atomic Number: 91
Atomic Weight: 231.0359
Electron Configuration (at ground state): 1s22s22p63s23p63d104s24p64d105s25p64f145d105f26s26p66d17s2
Oxidation States (Bold most stable): +5, +4
Boiling Point (K): 4300
Melting Point (K): 1845
Density (at 300K -- g/cm3): 15.4
Atomic Volume (at 300K -- cm3/mol) 15.0
Number of natural radioactive isotopes: 2
Mass Number (Bold naturally occurring) -- Half-Life -- Disintigration Type: 231 -- 3.28 x 104 -- alpha particle emission
Atomic Radius (Å): 1.61
First Ionization Potential (V): 5.88
Electronegativity (Pauling's): 1.5
Electrical Conductivity (at 293K for polycrystalline material -- 106 (ohms)-1 cm-1): 5.6
Thermal Conductivity (at 300K -- W m-1 K-1): 47
Crystal Structure: Orthorhombic
Acid-Base Properties: Slightly basic