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It's Elemental

The Element Protactinium

[Click for Isotope Data]


91 Pa Protactinium 231.03588

Atomic Number: 91

Atomic Weight: 231.03588

Melting Point: 1845 K (1572°C or 2862°F)

Boiling Point: Unknown

Density: 15.37 grams per cubic centimeter

Phase at Room Temperature: Solid

Element Classification: Metal

Period Number: 7

Group Number: none

Group Name: Actinide

Special Notes: Radioactive

What's in a name? From the Greek word for first, protos, and the element actinium, which together mean "the parent of actinium."

Say what? Protactinium is pronounced as PRO-tak-TIN-ee-em.

History and Uses:

Protactinium was first identified by Kasimir Fajans and O.H. Göhring in 1913 while studying uranium's decay chain. The particular isotope they found, protactinium-234m, has a half-life of about 1.17 minutes. They named the element brevium, meaning brief, and then continued with their studies. Protactinium's existence was confirmed in 1918 when another isotope, protactinium-231, was independently discovered and studied by two groups of scientists, Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of Great Britain. Protactinium was first isolated by Aristid V. Grosse in 1934.

Protactinium is a rare, poisonous and expensive element that is present in uranium ores in very small amounts. In 1961, the Great Britain Atomic Energy Authority was able to produce 125 grams of 99.9% pure protactinium, although they had to process about 55,000 kilograms of ore and spend about $500,000 to get it.

Protactinium's most stable isotope, protactinium-231, has a half-life of about 32,760 years. It decays into actinium-227 through alpha decay.

Due to its scarcity, high radioactivity and toxicity, there are currently no uses for protactinium outside of basic scientific research.

Estimated Crustal Abundance: 1.4×10-6 milligrams per kilogram

Estimated Oceanic Abundance: 5×10-11 milligrams per liter

Number of Stable Isotopes: 0 (View all isotope data)

Ionization Energy: 5.89 eV

Oxidation States: +5, +4

Electron Shell Configuration:


2s2   2p6

3s2   3p6   3d10

4s2   4p6   4d10   4f14

5s2   5p6   5d10   5f2

6s2   6p6   6d1


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For questions about this page, please contact Steve Gagnon.