Protactinium (Pa) – element 91
Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a actinide in group 3 (actinides), period 7 of the periodic table (f-block), and is a solid at room temperature.
Protactinium (Pa) has atomic number 91, atomic mass 231.04 u and electron configuration [Rn] 5f2 6d1 7s2.
Protactinium facts
| Symbol | Pa |
|---|---|
| Atomic number | 91 |
| Atomic mass | 231.04 u (g/mol) |
| Category | actinide |
| Group | group 3 (actinides) |
| Period | 7 |
| Block | f-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f2 6d1 |
| Noble-gas notation | [Rn] 5f2 6d1 7s2 |
| Electrons per shell | 2, 8, 18, 32, 20, 9, 2 |
Bohr model and shells
Protactinium has 91 electrons in 7 shells: 2, 8, 18, 32, 20, 9, 2. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 1841 K (1567.8 °C) |
|---|---|
| Boiling point | 4300 K (4026.8 °C) |
| Density | 15.37 g/cm³ |
| Electronegativity (Pauling) | 1.5 |
| Electron affinity | 53.03 kJ/mol |
| Ionization energies | 568 kJ/mol (1st) |
| Discovered by | William Crookes |
Use the atomic mass in the molar mass calculator for any formula containing Pa.
Position in the periodic table
Tap any element to open its page.
Frequently asked questions
What is the atomic mass of protactinium?
The atomic mass of protactinium is 231.04 u, so one mole of protactinium atoms weighs 231.04 g.
What is the electron configuration of protactinium?
Protactinium has 91 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f² 6d¹, or [Rn] 5f² 6d¹ 7s² in noble-gas notation. Electrons per shell: 2, 8, 18, 32, 20, 9, 2.
Is protactinium a metal?
Yes. Protactinium is a actinide.
Where is protactinium on the periodic table?
Protactinium is in group 3 (actinides), period 7, in the f-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.