About

Neptunium is the first transuranic element, meaning it has an atomic number greater than uranium, and is named after the planet Neptune. It is a radioactive, silvery actinide metal. It is primarily a byproduct of nuclear reactor operation and can be used to produce plutonium-238. It has some niche use in neutron detection instruments but is mainly of academic interest.

Atomic Properties

Atomic Number93

Atomic Weight237.048 u

Neutrons (common)144

Electron Configuration[Rn] 5f⁴ 6d¹ 7s²

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 5f⁴ 6d¹ 7s²

Electrons per Shell2, 8, 18, 32, 22, 9, 2

Electronegativity1.36

Electron Affinity45.85 kJ/mol

Oxidation States+7, +6, +5, +4, +3

Covalent Radius190 pm

Ionic Radius101 pm

Periodic Table Position

Group3

Period7

BlockF

Chemical SeriesActinoids

Physical Properties

State at STPsolid

Appearancesilvery metallic

Crystal Structureorthorhombic

Magnetic Orderingparamagnetic

Speed of Sound4,290 m/s

Thermal Properties

Melting Point917 K

Boiling Point4,174 K

Thermal Expansion0 1/K

Thermal Conductivity6.3 W/(m·K)

Specific Heat0.124 J/(g·K)

Molar Heat29.39 J/(mol·K)

Heat of Fusion5.19 kJ/mol

Heat of Vaporization336 kJ/mol

Abundance

In Earth's Crust0 ppm

Discovery

Discovered byEdwin McMillan, Philip H. Abelson

Discovery Year1,940

Occurrencesynthetic

CAS Number7439-99-8

Electron Configuration

Energy

↿⇂

1s

↿⇂

2s

↿⇂

2p

↿⇂

3s

↿⇂

3p

↿⇂

4s

↿⇂

3d

↿⇂

4p

↿⇂

5s

↿⇂

4d

↿⇂

5p

↿⇂

6s

↿⇂

4f

↿⇂

5d

↿⇂

6p

↿⇂

7s

↿

5f

↿

6d

7p

Isotopes of Neptunium

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
²³⁶Np	236.046670	—	153 ky	Electron Capture, Beta Minus Decay, Alpha Decay
²³⁷Np	237.048170	Trace	2.144 My	Alpha Decay