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Neptunium

Element 93 · Actinide

Specimen

Atomic number
93
Atomic mass
[237]
State at room temperature
Solid
Melting point
643.9 °C
Boiling point
3,902 °C
Density
20.25 g/cm³
Discovered
1940

Mass number of the longest-lived isotope, from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Radioactive. All neptunium is radioactive. Nuclear reactors make it, and uranium ores contain traces. Its radiation is the main danger. 3

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The atom

Np
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 18
4 (N) 32
5 (O) 22
6 (P) 9
7 (Q) outermost 2
Total93

Configuration [Rn] 5f⁴ 6d¹ 7s²

5f ↑ ↑ ↑ ↑
6d ↑
7s ↑ ↓
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 93 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Rn core, with one arrow per electron.

Related elements

Actinides
Ac Actinium Th Thorium Pa Protactinium U Uranium Pu Plutonium Am Americium Cm Curium Bk Berkelium Cf Californium Es Einsteinium Fm Fermium Md Mendelevium No Nobelium Lr Lawrencium

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Radioactive Elements .

    Mass number and half-life of the longest-lived isotope of the 34 elements with no standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    Royal Society of Chemistry, Periodic Table, 2026. Neptunium - Element information, properties and uses .

    Reference page; its Biological role and Natural abundance sections are quoted.

    • Neptunium has no known biological role. It is toxic due to its radioactivity. Natural abundance Neptunium is obtained as a by-product from nuclear reactors. It is extracted from the spent uranium fuel rods. Trace quantities occur naturally in uranium ores.