Protactinium
Definition and meaning of Protactinium in chemistry.
![Protactinium element card: symbol Pa, atomic number 91, atomic mass 231.04, electron configuration [Rn] 5f² 6d¹ 7s², oxidation states +5, Actinide, f-block, period 7, solid at room temperature.](/assets/images/terms/protactinium-chemical-element.webp)
Protactinium is a rare and highly radioactive element with the symbol Pa and atomic number 91. This dense, silvery gray metal belongs to the actinide series on the periodic table. It reacts easily with oxygen, water vapor, and inorganic acids in its solid state.
In more detail
Protactinium sits between thorium and uranium on the bottom rows of the periodic table. It is an extremely rare and expensive element to extract from natural rock ores. The most stable isotope is protactinium-231, which has a half-life of about 32760 years.
This isotope occurs in pitchblende at concentrations of only one part per million. The chemistry of protactinium is complex because it can lose different numbers of electrons. It usually exists in the +5 oxidation state but can also form a +4 state.
A common student misconception is that all radioactive elements are highly reactive with electricity. In fact, protactinium becomes a superconductor when cooled below 1.4 Kelvin. A superconductor conducts electric current with zero resistance, which is a very rare property.
Because of its intense radioactivity, this metal is highly toxic to all living things. Scientists must study this element inside specialized glove boxes that block radiation. Protactinium has no commercial uses because it is too rare and dangerous.
Scientists can only produce a few grams of this metal globally each year. Currently, it is only used for basic scientific research.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Pa |
| Atomic number | 91 |
| Atomic mass | 231.04 u |
| Category | Actinide |
| Year discovered | 1917 |
Scientists measure the amount of protactinium-231 in deep sea sediments to study ocean history. They compare it to thorium-230, which decays at a different rate. Because these elements settle to the ocean floor in predictable ways, their ratio changes over time. This dating method helps researchers calculate the exact age of sediment layers up to 150000 years old. Understanding these layers lets scientists reconstruct past changes in the global climate.
Frequently asked questions
Why is protactinium so rare on Earth?
It forms during the decay of uranium-235, which is a very rare isotope. Since protactinium also decays quickly, it never has time to accumulate in large amounts.
What does it mean when protactinium becomes a superconductor?
Below 1.4 Kelvin, the metal allows electric currents to flow without losing any energy as heat. This unique state lets electricity flow through the material forever without stopping.
What are the main hazards of handling protactinium?
Protactinium is a heavy metal that releases high-energy radiation as it decays. If it enters the body, it settles in organs and bones, causing severe radiation sickness.
Related terms
Sources & references
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