Nuclides
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Chemical element · Atomic number 91
Protactinium (Pa)
Actinides · Period 7 · Solid
Element identity
- Atomic number (Z)
- 91
- Symbol
- Pa
- Atomic weight / isotope mass number
- 231.035 88(1)
- Category
- Actinides
- Physical state (reference)
- Solid
- Period
- 7
- Group (reference)
- 3
- Block
- f
Physical properties
- Appearance
- Bright, silvery metallic luster
- Density
- 15.37 g·cm⁻³
- Melting point
- 1841 K / 1568 °C / 2854 °F
- Boiling point
- 4300 K / 4027 °C / 7280 °F
- Sublimation point
- Not available
Atomic and material properties
- Electron configuration
- [Rn] 5f² 6d¹ 7s²
- Electrons per shell
- K2 L8 M18 N32 O20 P9 Q2
- Oxidation states
- 2, 3, 4, 5
- Electronegativity (Pauling)
- 1.5
- Atomic radius
- Not available
- Covalent radius
- 200 pm
- Molar ionization energies
- 1st: 568 kJ·mol⁻¹ 2nd: 1128 kJ·mol⁻¹ 3rd: 1814 kJ·mol⁻¹ 4th: 2991 kJ·mol⁻¹
- Thermal conductivity
- 47 W·m⁻¹·K⁻¹
- Molar heat capacity
- Not available
- Crystal structure
- Tetragonal
- CAS number
- 7440-13-3
Property source: Wikipedia — Protactinium, adapted from the Nuclides App snapshot. Quoted conditions and qualifiers are retained.
Sources and interpretation
Snapshot exported 24 October 2026 from the element assets used by Nuclides. Properties are a reference compilation, not a new evaluation. Missing values are shown as “Not available”. Density and phase depend on temperature, pressure and allotrope; retained conditions are part of the quoted property.
Atomic weight is dimensionless. Parentheses give uncertainty in the last quoted digits. A single integer in square brackets is an isotope mass number, not a standard atomic weight. The snapshot can differ from current evaluations; consult CIAAW standard atomic weights and the IUPAC periodic table for current values and conventions.
Element properties in the App snapshot are adapted from Wikipedia. Each element page links to its source article; text adaptations are available under CC BY-SA 4.0. No third-party images are included.
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