Neptunium is a chemical element with symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. Neptunium metal is silvery and tarnishes when exposed to air. It is radioactive, poisonous, pyrophoric, and can accumulate in bones, which makes the handling of neptunium dangerous. .

Atomic Weight: 42
Density:       356 g/cm3
Melting Point: 635
Boiling Point: 345