Protactinium (symbol Pa, atomic number 91) is a rare, dense radioactive actinide with few practical uses. It is classified as a actinide and sits in the actinide series (f-block), period 7 of the periodic table.
Overview
Protactinium is the chemical element with atomic number 91 and the symbol Pa. With a standard atomic weight of [231], it is a actinide. In the periodic table it occupies the actinide series (f-block) and period 7, and under standard conditions it is normally a solid. Protactinium is a rare, dense radioactive actinide with few practical uses.
Atomic structure
An atom of Protactinium has 91 protons in its nucleus and, when neutral, 91 electrons arranged in the configuration [Rn] 5f2 6d1 7s2. Protactinium has no stable isotope; the value [231] refers to the mass number of its most stable or most commonly produced isotope.
Discovery and place in the table
Protactinium was discovered in 1913 by Kasimir Fajans, Oswald Helmuth Göhring. It follows Thorium (Th) and precedes Uranium (U) in order of atomic number.
| Atomic number | 91 |
|---|---|
| Symbol | Pa |
| Atomic mass | [231] |
| Category | Actinide |
| Group | — |
| Period | 7 |
| Electron configuration | [Rn] 5f2 6d1 7s2 |
| Phase at STP | Solid |
| Discovered | 1913 (Kasimir Fajans, Oswald Helmuth Göhring) |