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Information valid for Pa-231 unless otherwise noted

Basic Information

Symbol: Pa
Atomic Number: 91
Mass: 231.03587
Melting Point: 1600.0 C
Boiling Point: Unknown
Number of Protons/Electrons: 91
Number of Neutrons: 140
Classification: Rare Earth
Crystal Structure: Orthorhombic
Density @ 293 K: 15.4 g/cm3
Color: Unknown

Atomic Structure

[Bohr Model of Protactinium]
Number of Energy Levels: 7

  1. First Energy Level: 2
    Second Energy Level: 8
    Third Energy Level: 18
    Fourth Energy Level: 32
    Fifth Energy Level: 20
    Sixth Energy Level: 9
    Seventh Energy Level: 2


Isotope Half Life
Pa-230 17.4 days
Pa-231 32800.0 years
Pa-233 27.0 days
Pa-234 6.69 hours
Pa-234m 1.17 minutes


Date of Discovery: 1917
Discoverer: Fredrich Soddy
Name Origin: From the Greek word protos (first)
Uses: No uses known
Obtained From: fission product of uranium, thorium, plutonium