Neptunium (Np)

Neptunium is a chemical element with symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. Its position in the periodic table just after uranium, named after the planet Uranus, led to it being named after Neptune, the next planet beyond Uranus.

Atomic Number

93

Atomic Mass

237 u

Category

actinide

Phase

solid

Density

20.45 g/cm³

Electron Shells

2, 8, 18, 32, 22, 9, 2

Atomic Structure

Protons: 93 • Electrons: 93 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁴ 6d¹

Discovery

1940 • Edwin McMillan, Philip H. Abelson