Protactinium

Document v1 · published by Koskamo · updated 2026-10-04

Protactinium (Pa) is chemical element 91, an actinide in the f-block, period 7 (PubChem).

Atomic number: 91
Symbol: Pa
Group: none (f-block)
Period: 7
Atomic mass: 231.03588 u
Electron configuration: [Rn]7s2 5f2 6d1
Electronegativity (Pauling scale): 1.5
Atomic radius (van der Waals): 243 pm
Ionization energy: 5.89 eV
Oxidation states: +5, +4
Standard state: Solid
Melting point: 1845 K
Density: 15.37 g/cm³
Chemical group: Actinide
Year discovered: 1913

Source and provenance

Original source: pubchem.ncbi.nlm.nih.gov
Published on Koskamo by: Koskamo
Citation version: Document v1
Reuse: PubChem periodic table data (NIH/NLM, pubchem.ncbi.nlm.nih.gov/ptable); group and period from Jefferson Lab via PubChem

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Version history

Published by Koskamo2026-10-04
Version 1