Pa
Protactinium
Protactinium is a chemical element with the symbol Pa and atomic number 91. It has a standard atomic weight of 231.04, sits in period 7 of the f-block, and is classified as an actinide.
Properties
| Symbol | Pa |
|---|---|
| Atomic number | 91 |
| Standard atomic weight | 231.04 |
| Category | Actinide |
| Group | f-block — no group |
| Period | 7 |
| Electron configuration | [Rn] 5f3 7s2 |
| Outer-shell electrons | 2 |
The figure of 231.04 is a standard atomic weight.
Calculate with protactinium
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
Atomic weights are the IUPAC 2021 standard values, abridged to the conventional five significant figures. Group, period, category and electron configuration are derived from the atomic number rather than stored, so they cannot drift out of step with it.