091Actinide · Group 3 · Period 7
Protactinium
Protactinium (Pa) is element 91, a actinide in the f-block — group 3, period 7. It is a solid at room temperature with 7 electron shells (2, 8, 18, 32, 20, 9, 2) and an atomic mass of 231.035882 u.
- Atomic mass
- 231.0 u
- Phase · STP
- solid
- Melting
- 1841 K · 1568 °C
- Boiling
- 4300 K · 4027 °C
- Electronegativity
- 1.5
- Density
- 15.37 g/cm³
Photograph — ENERGY.GOV, Public domain, via Wikimedia Commons
Identity
- Atomic number
- 91
- Standard atomic weight
- 231.0 u
- Category
- Actinide
- Group
- 3
- Period
- 7
- Block
- f-block
- Oxidation states
- +5, +4
Physical properties
- Melting point
- 1841 K · 1568 °C
- Boiling point
- 4300 K · 4027 °C
- Density
- 15.37 g/cm³
- Molar heat capacity
- —
- Atomic radius
- 243 pm
- Electron affinity
- 53.03 kJ/mol
Atomic structure
91protons
140neutrons
91electrons
2valence e⁻
- Noble-gas notation
- [Rn] 5f2 6d1 7s2
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f2 6d1
- Electrons per shell
- 2, 8, 18, 32, 20, 9, 2
Periodic trends
Where Protactinium ranks across all 118 elements.
Discovery
- Discovered
- 1913
- Discovered by
- William Crookes
- Named by
- Otto Hahn
- Appearance
- bright, silvery metallic luster