Neptunium is element 93, an actinoid of the f block, in period 7. Its ground-state configuration is [Rn] 5f4 6d1 7s2, and it usually shows the oxidation states 0, 3, 4, 5, 6.
It was discovered in 1940, by McMillan and Abelson.
Name origin: Neptune, the eighth planet in the Solar System.
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