Symbol Np
Atomic Number 93
Atomic Mass 237 g.mol -1
Discovered by Edwin McMillan and Philip Abelson in 1940

Chemical Properties of Neptunium

Group Actinides Melting point 644°C, 1191°F, 917 K 
Period 7 Boiling point 3902°C, 7056°F, 4175 K
Block f Density (g cm−3) 20.2 
Atomic number 93 Relative atomic mass [237]    
State at 20°C Solid Key isotopes 237Np
Electron configuration [Rn] 5f46d17s2  CAS number 7439-99-8
ChemSpider ID 22375 ChemSpider is a free chemical structure database

What is Neptunium?

  • Neptunium has an atomic number of 93, present in the actinide series of on the Periodic Table.
  • Neptunium is found between uranium (92), the last of the natural elements, and plutonium (94).
  • Like its two closest neighbors, it belongs to the actinide series, so named because of the chemical affinity with actinium (89).
  • First, of the artificially produced elements, Np starts the series of the 11 transuranic elements, all radioactive, heavy metals.

Physical properties of Neptunium

  • Like plutonium and uranium, neptunium (237) is an alpha emitter, which means that as it disintegrates, it emits a particle formed of two protons and two neutrons (similar to a helium nucleus). It then transmutes into protactinium 233 (element 91).
  • Neptunium is produced through neutron bombardment of a uranium nucleus.
  • Plutonium 238 is obtained as a result of using Np 237 as a target in research reactors, which constitutes a significant source of energy for space missions.
  • Found in nuclear waste as a mixture with other fission products, Neptunium 237 also appears in increasing quantity as a product of americium 241.

Applications and effects of Neptunium

  • With a critical mass of 73 kg, Neptunium is considered usable in nuclear weapons. Although, no country is known to have used it to make a nuclear explosive device.
  • Np with no major commercial uses of Np is needed for research and exploratory work.

Practise This Question

The freezing point of benzene decreases by 0.45C when 0.2g of acetic acid is added to 20g of benzene. If acetic acid associates to form a dimer in benzene, percentage association of acetic acid in benzene will be
(Kf for benzene = 5.12K kg mol1)

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