Protactinium (Pa)
Isotopes of Protactinium
| Isotope | Atomic Mass | Half-life | Mode of Decay | Nuclear Spin | Nuclear Magnetic Moment |
| Pa-228 | 228.03100 | 22 hours | EC to Th-228; α to Ac-224 |
3 | 3.5 |
| Pa-229 | 229.03209 | 1.50 days | EC to Th-229; α to Ac-225 |
5/2 | No data available |
| Pa-230 | 230.03453 | 17.04 days | EC to Th-230; α to Ac-226; β- to U-230 |
2 | 2.0 |
| Pa-231 | 231.035880 | 32,500 years | α to Ac-226; SF | 3/2 | 2.01 |
| Pa-232 | 232.03858 | 1.31 days | EC to Th-232; β- to U-232 |
2 | No data available |
| Pa-233 | 233.04024 | 27.00 days | β- to U-233 | 3/2 | 4.0 |
| Pa-234 | 234.04330 | 6.69 hours | β- to U-234 | 4 | No data available |
Protactinium was discovered in 1913 by Otto Hahn, Lise Meitner, Frederick Soddy and John Cranston. Its name originates with the Greek word protos, meaning “first.”
A shiny white metal with bright metallic luster, protactinium is also hard and malleable, with a body-centered tetragonal structure. It has a vapor pressure of 3.88 x 10-2 torr at about 1930 ºC and is superconducting below -271.75 °C. In solution, Pa4+ is oxidized to Pa5+ by atmospheric oxygen. The chemistry of pentavalent protactinium is quite similar to that of niobium and tantalum. A number of salts and complexes are known. No commercial application of protactinium isotopes is known outside of scientific research. For this purpose, protactinium is generally extracted from spent nuclear fuel.
Protactinium is a very dangerous substance to work with. It is highly toxic and presents a radiation hazard (alpha emitter). The Proactinium-231 isotope is a long-lived alpha-emitter and is not excreted readily. Exposure can cause cancer.
Properties of Protactinium
| Name | Protactinium |
| Symbol | Pa |
| Atomic number | 91 |
| Atomic weight | 231.03588 |
| Standard state | Solid at 298 ºK |
| CAS Registry ID | 7440-13-3 |
| Group in periodic table | N/A |
| Group name | Actinoid |
| Period in periodic table | 7 (Actinoid) |
| Block in periodic table | f-block |
| Color | Silvery metallic |
| Classification | Metallic |
| Melting point | 1568 °C |
| Boiling point | 4000 °C |
| Thermal conductivity | 47 (estimate) W/(m·K) |
| Electrical resistivity | 18 x 10-8 Ω·m |
| Electronegativity | 1.5 |
| Heat of vaporization | 470 kJ·mol-1 |
| Heat of fusion | 15 kJ·mol-1 |
| Density of solid | 15.370 g/cm3 |
| Electron configuration | [Rn]5f26d17s2 |
| Atomic radius | 1.63 Å (coordination number 12) |
| Oxidation states | +4, +5 |
