Neptunium
[Rn] 5f⁴ 6d¹ 7s² · 2 · 8 · 18 · 32 · 22 · 9 · 2
The first transuranium element — the first box beyond uranium that humans filled themselves. Neptunium is named after the planet beyond Uranus, by exactly the logic that puts the element beyond uranium.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 93
- Atomic mass
- 237 а.е.м. ≈
- Electron configuration
- [Rn] 5f⁴ 6d¹ 7s²
- Electrons per shell
- 2 · 8 · 18 · 32 · 22 · 9 · 2
- Block
- f-block
- Group
- no data
- Period
- 7
- Electronegativity (Pauling)
- 1.36
- Electronegativity (Allen)
- 1.22
- Atomic radius
- 221 pm
- Covalent radius
- 190 pm
- Van der Waals radius
- 221 pm
- Ionisation energy 1
- 604.5 kJ/mol
- Electron affinity
- 45.9 kJ/mol
- Common oxidation states
- +5
- Oxidation states
- +3, +4, +5, +6, +7
Physical properties
- State at 25 °C
- solid
- Density
- 20.45 g/cm³
- Melting point
- 917 K · 643.9 °C
- Boiling point
- 4 273 K · 3 999.9 °C ≈
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 5.19 kJ/mol
- Heat of vaporisation
- 336 kJ/mol ≈
- Specific heat capacity
- 0.12 J/(g·K)
- Thermal conductivity
- 6.3 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 1 220 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- orthorhombic
- Lattice constants
- a = 472.3 pm · b = 488.7 pm · c = 666.3 pm
Abundance
- In the crust
- does not occur
- In the ocean
- does not occur
- In the universe
- does not occur
- In the human body
- does not occur
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 236Np | — | 154 007.27 yr | ЭЗ |
| 237Np | — | 2.14 Myr | α |
Neptunium-237, half-life 2.14 million years, is the longest-lived isotope and one of the principal long-lived components of nuclear waste.
Discovery
- Year of discovery
- 1940
- Discovered by
- Edwin McMillan and Philip Abelson
- Where
- Berkeley, USA
- Origin of the name
- after Neptune, the planet beyond Uranus, as it follows uranium
History
McMillan and Abelson synthesised neptunium at Berkeley in 1940 by irradiating uranium with neutrons and finding a product with new chemistry. The discovery showed the table does not stop at uranium and opened the whole of transuranium chemistry.
Where it occurs
Traces in uranium ores from neutron capture. Effectively absent from nature.
How it is produced
As a reactor by-product: neptunium-237 accumulates in spent fuel, at a world total of tens of kilograms a year.
Role in living things
No biological role.
Safety
Radiotoxic. Neptunium-237 has a critical mass of about 60 kg, so it is tracked under non-proliferation rules.
Uses
- A target for breeding plutonium-238 for space power sources
- High-energy neutron detectors
- Research into transmutation of nuclear waste
Curiosities
- Neptunium was the first element humans made beyond the natural series — three years before plutonium.
- Neptunium-237 heads the fourth decay series, which has died out entirely in nature: its longest-lived member is too short-lived against the age of the Earth.
- Neptunium is named after Neptune, as uranium is after Uranus and plutonium after Pluto.
- Its discovery showed the periodic table could be extended artificially.