91Pa231.036
Actinidef-blockRadioactive
Protactinium
Element 91 on the periodic table, symbol Pa, group 3, period 7.
Protactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states.
Appearance: bright, silvery metallic luster
Properties
- Atomic Number
- 91
- Atomic Mass
- 231.0359 u
- Group
- 3
- Period
- 7
- Block
- f-block
- Category
- Actinide
- State at 25 °C
- Solid
- Melting Point
- 1,841 K · 1,567.9 °C
- Boiling Point
- 4,300 K · 4,026.9 °C
- Density
- 15.37 g/cm³
- Atomic Radius
- 180 pm
- Electronegativity
- 1.5
- Oxidation States
- +4, +5
- Abundance in Crust
- 1.40e-6 mg/kg
- Discovered
- 1913
- Discovered By
- William Crookes
Electron Configuration
[Rn] 5f2 6d1 7s2
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f2 6d1
Ionisation Energies (kJ/mol)
- 1. 568
Elements near Protactinium
Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.