Nẹ́ptúníọ̀m tabi Neptunium je apilese kemika pelu ami-idamo Np ati nomba atomu 93. Criticality of a 237Np Sphere Np(II), (III) and (IV) have been observed, see Dutkiewicz, Michał S.; Apostolidis, Christos; Walter, Olaf; Arnold, Polly L (2017). "Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding". Chem. Sci. 8 (4): 2553–2561. doi:10.1039/C7SC00034K. PMC 5431675. PMID 28553487. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5431675.  Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.