Pa
Protactinium
PROTACTINIUM
TRANSITION ELEMENT: ACTINIDE
| Atomic number: | 91 |
| Group numbers: | 3 |
| Period: | 7 |
| Electronic configuration: | [Rn] 5f2 6d1 7s2 |
| Formal oxidation number: | +4 +5 |
| Electronegativities: | 1.5 |
| Atomic radius / pm: | 156.1 |
| Relative atomic mass: | 231.035 88(2) |
Protactinium was discovered by Kasimir Fajans and Otto H. Göhring (DE) in 1913. The origin of the name comes from the Greek word protos meaning first. It is a very rare, silvery-white, extremely radioactive metal that resists alkalis, reacts with oxygen, acids and steam. Protactinium is highly radiotoxic, extremely toxic and must be handled with great care. Protactinium does not occur in nature. It is found among fission products of uranium, thorium and plutonium.
| Density / g dm-3: | 15370 | (calc.) |
| Molar volume / cm3mol-1: | 15.03 | (calc.) |
| Electrical resistivity / µΩcm: | 19.1 | (20 °C) |
| Thermal conductivity / W m-1K-1: | 47 |
| Melting point / °C: | 1572 |
| Boiling point / °C: | - |
| Heat of fusion / kJ mol-1: | 16.7 |
| Heat of vaporization / kJ mol-1: | 481 |
| Heat of atomization / kJ mol-1: | 607 |
| First ionization energy / kJ mol-1: | 568.30 |
| Second ionization energy / kJ mol-1: | - |
| Third ionization energy / kJ mol-1: | - |
| in the atmosphere / ppm: | - |
| in the Earth's crust / ppm: | 2E-12 |
| in the oceans / ppm: | - |
| Crystal structure: | body-centered tetragonal |
| Unit-cell dimensions / pm: | a=393.2, c=323.8 |
| Space group: | I4/mmm |
| Isotope | Relative atomic mass | Mass percent (%) |
|---|---|---|
| 231Pa | 231.035 88(2) | * |
| 233Pa | 233.040 25(2) | * |
| Balanced half-reaction | Eo / V | |
|---|---|---|
| 90 Thorium | ← | 91 Protactinium | → | 92 Uranium |
Citing this page:
Generalic, Eni. "Protactinium." EniG. Periodic Table of the Elements. KTF-Split, 18 Jan. 2024. Web. {Date of access}. <https://www.periodni.com/pa.html>.
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