Element / isotope identity
Element 91 and 231Pa reference data are evaluated.
Tetragonal metal
The ordinary metallic structure is reported as tetragonal I4/mmm; the viewer is a simplified conventional cell.
Phase data
Melting/boiling references are evaluated for the teaching path.
Geochemistry
Pa isotope applications are explained conceptually without separation or handling methods.
Safety boundary
No production, acquisition, purification or source-preparation instructions.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Protactinium (Pa)
Protactinium is element 91, a scarce radioactive actinide found only in trace amounts in uranium ores. ²³¹Pa is long-lived on human timescales, and the element’s story links early actinide chemistry, tetragonal metal structure and decay-series geochemistry.
Protactinium atomic number, mass, electron configuration and key properties
Protactinium: quick answers
How many protons, neutrons and electrons does protactinium have?
Protactinium’s atomic number is 91, so every protactinium atom has 91 protons, and a neutral atom also has 91 electrons. Its most common natural isotope, protactinium-231, has 140 neutrons (other isotopes have different neutron counts).
What is the symbol for protactinium?
The chemical symbol for protactinium is Pa.
Is protactinium a solid, liquid or gas at room temperature?
Protactinium is a solid at room temperature (about 25 °C).
What family (group) is protactinium in?
Protactinium is an actinide, in period 7 (the f-block row shown below the main table) of the periodic table.
What is the electron configuration of protactinium?
The ground-state electron configuration of protactinium is [Rn] 5f² 6d¹ 7s².
From atomic number to chemistry
Read these as a chain of causes, not as isolated facts. Each step links to the concept hub if you want the underlying idea explained.
91 protons define protactinium.
The reference ground-state configuration frames atomic and chemical behavior.
Periodic position organizes recurring trends without replacing element-specific evidence.
The teaching nucleus is one isotope, not the relative atomic mass.
Phase claims are evidence-labelled; unknown superheavy bulk boundaries are not fabricated.
Protactinium in its period and family
Protactinium sits between thorium and uranium in the early actinides. Its f/d electron occupancy and common +5 state make it a useful bridge in actinide chemistry.
Protactinium Visual Lab
Inspect a ²³¹Pa nucleus, representative 5f/6d/7s probability models and a tetragonal metal cell, then connect +5/+4 chemistry, uranium-decay occurrence, discovery history and isotope-geochemistry applications.
Every mark points to one exact feature
The numbered markers explain the same information system used throughout Element Lookup. Unknown or predicted fields remain visibly labelled rather than being replaced with guesses.
Protactinium in one minute
Atomic number 91 means 91 protons.
The ground-state reference is [Rn] 5f² 6d¹ 7s².
²³¹Pa is the key natural isotope and is radioactive.
Protactinium metal has a tetragonal structure under ordinary conditions.
Protactinium has little use outside research; no production or handling guidance is provided.
Shell rings organize electron counts. They are not electron trajectories or orbital shapes.
2 · 8 · 18 · 32 · 20 · 9 · 2 electrons
The representative 6d and 5f clouds illustrate angular probability patterns for isolated-atom teaching. They are not direct maps of chemical bonds, radioactivity or the tetragonal metal band structure.
Protactinium is represented with a body-centred tetragonal teaching cell consistent with reported room-temperature metallic structure. The viewer is a simplified conventional cell.. The viewer is evidence-aware: measured structures are identified as such; unknown bulk structures stay unknown.
Teaching visualization; not a literal finite sample or thermal trajectory.What this model does—and does not—show
The representative 6d and 5f clouds illustrate angular probability patterns for isolated-atom teaching. They are not direct maps of chemical bonds, radioactivity or the tetragonal metal band structure.
Where do I meet protactinium?
Clickable learning cards connect the element to materials, environment, technology, biology or research - depending on what the evidence actually supports.
Trace natural occurrence
Small amounts of ²³¹Pa occur in uranium ores through decay-series processes.
Early actinide: 5f/6d electrons, +5 chemistry and isotope geoscience
Protactinium connects the emergence of 5f chemistry with a long-lived natural isotope and specialized Earth-science tracers.
Long-lived natural isotope
231Pa occurs in uranium decay systems and is the main natural protactinium reference.
Thorium, protactinium and uranium
Compare the early actinides as 5f occupancy grows and multiple oxidation states emerge.
| Z | 90 |
|---|---|
| Key state | +4 |
| Z | 91 |
|---|---|
| Key state | +5 |
| Z | 92 |
|---|---|
| States | +3 to +6 |
Protactinium properties: atomic, physical, thermal and chemical
Categories follow the science of this element rather than a fixed decorative template. Each row carries condition/provenance context and an evidence label; unknown values stay unknown.
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Atomic number | 91 | Source-reviewed; see Sources below | Evaluated |
| Relative atomic mass | 231.036 | Source-reviewed; see Sources below | Evaluated |
| Ground-state electron configuration | [Rn] 5f² 6d¹ 7s² | Source-reviewed; see Sources below | Evaluated |
| Group / period / block | Group Actinides · Period 7 · f-block | Periodic-table placement | Evaluated |
| Electronegativity | 1.5 (approx.) | Source-reviewed; see Sources below | Evaluated |
| Reference isotope | ²³¹Pa | Source-reviewed; see Sources below | Evaluated |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| State context | Silvery radioactive solid | Source-reviewed; see Sources below | Evaluated |
| Density | 15.4 g/cm³ | Source-reviewed; see Sources below | Evaluated |
| Material / molecular structure | Protactinium metal · tetragonal I4/mmm | Protactinium is represented with a body-centred tetragonal teaching cell consistent with reported room-temperature metallic structure. The viewer is a simplified conventional cell. | Measured |
| Classification | Actinide | Periodic-table / chemistry classification | Evaluated |
| Structure-model scope | Protactinium is represented with a body-centred tetragonal teaching cell consistent with reported room-temperature metallic structure. The viewer is a simplified conventional cell. | Teaching visualization; exact crystallographic coordinates are not implied unless stated. | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Melting / transition reference | 1845 K | Source-reviewed; see Sources below | Evaluated |
| Boiling / gas reference | 4273 K | Source-reviewed; see Sources below | Evaluated |
| Phase-path context | At approximately standard pressure, protactinium is treated as a tetragonal solid below about 1845 K, liquid to about 4273 K and gaseous above the evaluated boiling reference. | Shared phase registry drives the slider, regions and markers. | Evaluated |
| Condition warning | Temperature and pressure define phase behavior; purity/allotropy may matter. | Teaching condition statement | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Common oxidation states | +5, +4 | Source-reviewed; see Sources below | Evaluated |
| Ion / common ion context | Pa⁵⁺ | Source-reviewed; see Sources below | Evaluated |
| Periodic chemistry context | Protactinium sits between thorium and uranium in the early actinides. Its f/d electron occupancy and common +5 state make it a useful bridge in actinide chemistry. | Element-specific interpretation | Reviewed |
| Chemistry caution | Elemental form, ions and compounds are distinct chemical objects. | Interpretive teaching rule | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| ²³¹Pa | Radioactive · key natural isotope | Reference teaching nucleus with 91 protons and 140 neutrons; long-lived compared with many radionuclides. | Evaluated |
| ²³⁴mPa | Short-lived decay-series isotope | Historically linked to the early discovery of protactinium/brevium. | Evaluated |
| ²³³Pa | Radioactive research isotope | Appears in nuclear-decay/transmutation studies under controlled conditions. | Evaluated |
| Teaching nucleus | ²³¹Pa · 91 protons + 140 neutrons | Reference isotope used in the nucleus model | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Page evidence note | Atomic/phase values are evaluated. The tetragonal structure is a reviewed bulk-metal reference. Isotope-geochemistry is discussed conceptually; all radioactive-material operations remain out of scope. | Evidence summary for this guide | Reviewed |
| Structure evidence | Protactinium is represented with a body-centred tetragonal teaching cell consistent with reported room-temperature metallic structure. The viewer is a simplified conventional cell. | Measured structure, labelled schematic, prediction or explicit unknown as applicable. | Reviewed |
| Map evidence rule | Real pins are reviewed examples; conceptual layers are used when pins would mislead. | Geography Explorer 2.0 | Reviewed |
| Source set | 3 primary/reference links listed below | Open the Sources section for the actual references. | Reviewed |
Is Protactinium a solid, liquid or gas? State at temperature
At approximately standard pressure, protactinium is treated as a tetragonal solid below about 1845 K, liquid to about 4273 K and gaseous above the evaluated boiling reference.
Where on Earth is Protactinium found or produced?
Who discovered Protactinium, and when?
Kasimir Fajans and Oswald Göhring identified a short-lived isotope then called brevium.
Lise Meitner and Otto Hahn identified the much longer-lived ²³¹Pa, establishing protactinium more firmly.
Researchers isolated enough protactinium for more detailed chemical study.
Protactinium remains a specialist research element and a useful isotope-system tracer in Earth science.
Protactinium: trace decay-series occurrence to research measurement
Protactinium occurs naturally only in very small quantities within uranium decay systems.
Research measurements use specialized radiochemical separation and detection under licensed conditions; no separation method is provided here.
Geochemical studies can use Pa isotope ratios as tracers of processes such as particle transport and past ocean circulation.
The educational focus is identity, evidence and interpretation rather than acquisition or handling.
What is protactinium used for?
Research chemistry
Protactinium is used almost entirely for scientific research into actinide chemistry and nuclear properties.
Geochemical tracers
Pa/Th isotope systems support specialized paleoceanography and sediment-process studies.
Nuclear-data science
Protactinium isotopes contribute to decay-series and nuclear-property research.
Historical science
Its discovery history illustrates how isotope identification reshaped the periodic table.
Protactinium isotopes and natural abundance
²³¹Pa
Radioactive · key natural isotopeReference teaching nucleus with 91 protons and 140 neutrons; long-lived compared with many radionuclides.
²³⁴mPa
Short-lived decay-series isotopeHistorically linked to the early discovery of protactinium/brevium.
²³³Pa
Radioactive research isotopeAppears in nuclear-decay/transmutation studies under controlled conditions.
Five-question Protactinium check
What is protactinium’s atomic number?
Which isotope is the key natural reference?
What is the ordinary metal structure?
What is a major oxidation state?
What kind of modern application is scientifically important?
Protactinium questions students commonly ask
Each answer starts with the direct fact, then explains the chemistry, evidence or material context so the result is understandable rather than merely memorized.
What is protactinium’s atomic number?
Short answer: 91.
Atomic number is defined by proton count, so 91 protons are what make an atom protactinium. A neutral protactinium atom also has 91 electrons, while isotopes can have different neutron counts without changing the element.
Key point: Atomic number = proton count.
Is protactinium a metal?
Short answer: Yes. It is a radioactive actinide metal.
This guide classifies Protactinium as an actinide. Its periodic position is Period 7, f-block, Group Actinides. Protactinium sits between thorium and uranium in the early actinides. Its f/d electron occupancy and common +5 state make it a useful bridge in actinide chemistry.
Key point: Periodic-table classification describes recurring atomic/chemical behavior; it does not make every element in a column physically identical.
What is protactinium used for?
Short answer: Mostly scientific research; Pa isotope systems also have geochemical/paleoceanographic uses.
Research chemistry: Protactinium is used almost entirely for scientific research into actinide chemistry and nuclear properties. Geochemical tracers: Pa/Th isotope systems support specialized paleoceanography and sediment-process studies. Protactinium is scientifically important but has almost no everyday use. Its scarcity and radioactivity mean that evidence comes from specialized research, and operational nuclear-material information does not belong on this learning page.
Key point: Always distinguish the pure element from the compound, alloy, isotope or device material that actually performs the application.
Where is protactinium found?
Short answer: In trace amounts in uranium ores and natural decay-series systems.
Protactinium occurs naturally only in very small quantities within uranium decay systems. Trace natural occurrence Small amounts of ²³¹Pa occur in uranium ores through decay-series processes.
Key point: Natural occurrence, resources, production and recycling are different geography questions.
What are common oxidation states?
Short answer: +5 is especially important, with +4 also established.
Protactinium sits between thorium and uranium in the early actinides. Its f/d electron occupancy and common +5 state make it a useful bridge in actinide chemistry. Protactinium is scientifically important but has almost no everyday use. Its scarcity and radioactivity mean that evidence comes from specialized research, and operational nuclear-material information does not belong on this learning page.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
Does this page explain how to isolate protactinium?
Short answer: No. Operational separation, acquisition and handling guidance is intentionally excluded.
Protactinium is scientifically important but has almost no everyday use. Its scarcity and radioactivity mean that evidence comes from specialized research, and operational nuclear-material information does not belong on this learning page. Protactinium is radioactive and toxic. This page contains no production, separation, source fabrication, acquisition or handling instructions.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
Scientific sources for Protactinium
- Royal Society of Chemistry - Protactinium
- NIST - Atomic Data for Protactinium
- WebElements - Protactinium crystal structure
Questions to ask next about Protactinium
A good element lesson should lead to the next useful question, not end after a list of facts.
Found an error, something unclear, or a missing topic?
Tell us what you noticed. Feedback goes to a private review queue and is never published automatically.