91Pa231.03588
Protactinium
Actinide
Solid at STP
Period 7Block FDiscovered 1913
[Rn]7s2 5f2 6d1
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.
📖 Read more on Wikipedia →Atomic Properties
| Atomic Number | 91 |
| Atomic Mass | 231.03588 u |
| Electron Configuration | [Rn]7s2 5f2 6d1 |
| Oxidation States | +5, +4 |
| Electronegativity | 1.5 (Pauling) |
| Atomic Radius | 243 pm |
| Ionization Energy | 5.89 eV |
| Block | F |
Physical Properties
| Appearance | bright, silvery metallic luster |
| Standard State | Solid |
| Melting Point | 1845 K (1571.8 °C) |
| Density | 15.37 g/cm³ |
| CPK Color | #00A1FF |
Classification
| Category | Actinide |
| Group Block | Actinide |
| Period | 7 |
| Block | F |
Discovery
| Year Discovered | 1913 |
| Discovered By | William Crookes |
| Named By | Otto Hahn |
| Electron Shells | 2, 8, 18, 32, 20, 9, 2 |