Element 91
Protactinium
Actinides
Protactinium (Pa) is in the f-block of the periodic table — group 3, period 7.
Protactinium is a chemical element with symbol Pa and atomic number 91.
Key data
- Atomic number
- 91
- Atomic mass
- 231.036 u
- Group / Period
- 3 / 7
- Block
- f-block
- Phase at STP
- Solid
- Density
- 15.37 g/cm³
- Melting point
- 1567.8 °C
- Boiling point
- 4026.8 °C
- Electron configuration
- [Rn] 5f2 6d1 7s2
Periodic table block
Protactinium is in the f-block (group 3, period 7). Elements land in the f-block when their highest-energy electrons fill an f subshell — these are the lanthanides and actinides shown beneath the main table.
New to this? Periodic table blocks explained: s, p, d, and f
Common uses
- •Research only
- •Radioactive
- •Decay product of uranium
Discovery
Year: 1913
Discovered by: William Crookes
Named by: Otto Hahn
Frequently asked questions
What is the atomic number of Protactinium?
Protactinium has atomic number 91. Its symbol is Pa and its atomic mass is 231.036 u.
What category of element is Protactinium?
Protactinium is classified as actinides. It sits in group 3, period 7 of the periodic table.
What block of the periodic table is Protactinium in?
Protactinium is in the f-block (group 3, period 7). Its highest-energy electrons occupy the f subshell — you can see this in its electron configuration, [Rn] 5f2 6d1 7s2.
What is Protactinium used for?
Common uses of Protactinium include: Research only, Radioactive, Decay product of uranium.
When was Protactinium discovered?
Protactinium was discovered in 1913 by William Crookes.
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