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.
Three reasons Protactinium stands out
- 1
Radioactive metal, used in nuclear reactors and some research applications.
- 2
Its name literally means "before actinium," as it decays radioactively to produce actinium.
- 3
It is found only in tiny trace amounts as a decay product inside uranium ores.
A rare pause in uranium’s decay
Protactinium sits between uranium and actinium in a decay chain, which is exactly what its name announces. It is scarce, radioactive, and difficult to handle, so it has few uses outside research. Its complex electron behavior gives chemists a challenging bridge between lighter and heavier actinides.