93
Np
Neptunium
237
Neptunium (Np)
ActinidePeriod 7f-block-blockRadioactive
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.
Latin name: Neptunium
Atomic Number
93
Atomic Mass
237 g/mol
Phase (STP)
Solid
Electron Config.
[Rn] 5f⁴ 6d¹ 7s²
General
SymbolNp
Atomic Number93
Atomic Mass237 g/mol
CategoryActinide
Period7
Blockf-block
Electron Configuration[Rn] 5f⁴ 6d¹ 7s²
Valence Electrons7
Coloursilvery metallic (very reactive)
Appearancesilvery metallic
CAS NumberCAS7440-14-4
Physical Properties
Phase (STP)Solid
Density20.45 g/cm³
Melting Point638.85°C · 1181.93°F · 912.00 K
Boiling Point3999.85°C · 7231.73°F · 4273.00 K
Atomic Properties
Atomic Radius221 pm
Electronegativity1.36 Pauling
Ionization Energy605 kJ/mol
Oxidation States+5, +4, +3, +2
Ion ChargeNp3+/Np4+/Np5+
Thermodynamic
Molar Heat29.46 J/(mol·K)
Crystal Structure
Crystal Structurehexagonal close-packed
Nuclear & Hazards
RadioactiveYes
Half-life2.14×10^6 years (Np-237)
Abundance
In Universe0.00000000001%
In Earth's Crust0.00000000001%
Discovery & History
Discovery Year1940
Discovered ByEdwin McMillan and Philip H. Abelson (discovered 1940)
Country of DiscoveryUSA
Isotopes of Neptunium
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| Np-236 | — | 1.54 × 10⁵ years | EC, β⁻ |
| Np-237 | — | 2.144 × 10⁶ years | α |
| Np-239 | — | 2.356 days | β⁻ |