Periodic Table


Atomic number: 91
Atomic weight: 231.03588
Symbol: Pa
Group number: (actinide)
Electronic configuration: [Rn].5f2.6d1.7s2


Protactinium has a bright metallic lustre which it retains for some time in air. The element is superconductive below 1.4 K. The element is a dangerous toxic material and requires precautions similar to those used when handling plutonium. Protactinium is one of the rarest and most expensive naturally occurring elements. The element is an a-emitter and is a radiological hazard similar to polonium. Protactinium is a highly toxic and radioactive rare earth metal that requires special handling. It is found in pitchblende and ores form Zaire and is one of the rarest and most expensive naturally occurring elements.

General information

Discoveror: Otto Hahn, Lise Meitner, Frederick Soddy, John Cranston
Date discovered: 1913
Discovered at: Germany, England
Meaning of name: From the Greek word "protos" meaning "first"

Physical data

Standard state: solid at 298 K
Colour: silvery metallic
Density of solid at ambient temperature/kg m-3: 15370
Molar volume/cm3: 15.18

Radii /pm

Atomic: no data
Covalent (single bond):
Pauling radius for the ion [Pa]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius228.6no data124.054.7


Both values are quoted on the Pauling scale.

Pauling: 1.5
Allred Rochow: 1.14

Crystal Structure

structure: tetragonal

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 1841
boiling point: 273

Enthalpies /kJ mol-1

fusion: 14.5
vaporization: 481

single bond enthalpies:
Pa-F Pa-Cl Pa-Br Pa-I Pa-Pa
no data no data no data no data no data

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/Pa.html