Neptunium is a radioactive element obtained from nuclear-reactor materials, with trace natural occurrence in uranium ores. Neptunium-237 has been used in neutron detectors. Its position beyond uranium connects the periodic table to nuclear transformations and to research in which isotope identity carries essential information.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
Why is a neptunium precursor different from a spacecraft power source?
Neptunium-237 as a precursor to plutonium-238
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Place the precursor upstream
Neptunium-237 has a role in producing plutonium-238 for space programs. Its position in the supply chain differs from the role of the final heat-producing fuel.
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NpFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
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Which description preserves the supply-chain distinction?
Atomic identity, reference properties and structure models
INTERACTIVE 3D93 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Rn] 5f4 6d1 7s2. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
Edwin McMillan and Philip Abelson identified neptunium at Berkeley in 1940, establishing an element beyond uranium. Earlier interpretations of uranium experiments had confused new elements with products later understood through nuclear . Neptunium’s name followed the planetary sequence from Uranus to Neptune. Its discovery helped turn the transuranium elements from a speculative extension of the periodic table into a program of experimentally accessible nuclear and chemical research.
1940
Element established
McMillan and Abelson identify neptunium.
2015
Space-fuel milestone
Oak Ridge reports newly produced plutonium-238 using neptunium feedstock.
Neptunium is chiefly encountered as a product of nuclear reactions in irradiated uranium-containing material. Extremely small natural traces can also arise from nuclear processes in uranium . Its presence therefore requires an origin story: primordial , continuing natural production and human manufacture are different sources of an element.
Neptunium has several accessible , so its chemical form can change how it binds to oxygen-containing molecules or moves through a material. The listed configuration describes a neutral atom. It should not be read as the electron arrangement of every neptunium in a solution or .
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
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Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
solid
293.15 K, 101.325 kPa
Melting point in K
917 K
at standard pressure unless noted
Boiling point in K
4273 K
101.325 kPa
Density in g/cm³
20.45 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
1.36 Pauling
Pauling scale
First ionization energy in kJ/mol
604.5 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
190 pm
single-bond covalent radius
Common oxidation states
+5
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust
Not recorded
upper continental crust, mass fraction
Has stable isotopes
Noderived
Discovery year in CE
1940 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 7
Np 1.36 Pauling · Neptunium
Electronegativity across period 7. Exact values.
Ra
0.9
Ac
1.1
Th
1.3
Pa
1.5
U
1.38
Np
1.36
Pu
1.28
Am
1.13
Cm
1.28
Bk
1.3
Cf
1.3
Es
1.3
Fm
1.3
Md
1.3
No
1.3
Lr
1.3
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
