Protactinium is element 91, an actinoid of the f block, in period 7. Its ground-state configuration is [Rn] 5f2 6d1 7s2, and it usually shows the oxidation states 0, 4, 5.
It was discovered in 1917, by Soddy, Cranston, Meitner and Hahn.
Name origin: the Greek protos, 'first', and actinium, which is produced through the radioactive decay of protactinium.
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