Protactinium

Atomic symbol: Pa
Atomic number: 91
Atomic mass: 231.04

Appearance: Bright silver yellow solid at 25°C

Group: N/a Period: 7
Series: Actinides
Block: f
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f² 6d¹ 7s²

A toxic and radioactive metal with a very short half life.

Produced through uranium decay.

Fun Fact! Combined with thorium, protactinium is used to date marine sediments.