Neptunium

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What is Neptunium?

Neptunium is a chemical element which is the 5th member of the Actinide series and is placed in the 7th period. Symbol of the Neptunium element is Np. It is a metal which is the first transuranic element. Its atomic number is 93. Promethium which is a member of the lanthanide series is placed above neptunium in the periodic table. Another metal plutonium is found at the right of neptunium and uranium is present at its left in the 7th period of the periodic table. Uranium and plutonium metals are also members of the actinide series. Neptunium is a member of f – block elements. As it is present after uranium, so it is called a transuranic element. It is a silvery metal which gets corroded when exposed to air. It must be handled very carefully as it is a radioactive and poisonous metal. Most of the neptunium metal is produced in nuclear power reactors using uranium. 

Neptunium is the 1st synthetic transuranium metal. Many false claims were made for its discovery. But the 1st time it was originally synthesized by American physicists Edwin McMillan and Philip H. Abelson at Berkeley Radiation Laboratory in 1940. Edwin McMillan got the Nobel prize for synthesizing the transuranium element. They used uranium to synthesize the neptunium element. They prepared a larger sample of bombarded uranium and showed following reaction –

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Neptunium is named after the planet Neptune. According to Roman mythology, Neptune is a god of the sea. The word is taken from Latin word Neptunus and Neptune is identified with the Greek god Poseidon. Neptunium is not found in pure elemental form in nature as it is a synthetic element and forms by nuclear reaction of uranium. It generally forms a green coating of its oxide when exposed to moist air. It is a hard, ductile, radioactive and silvery colored actinide metal. 

Neptunium is found in its three allotropic forms – – neptunium, – neptunium and – neptunium. All three allotropes of neptunium show different symmetry in structure. – neptunium has orthorhombic structure, – neptunium has tetragonal structure and – Neptunium has a body centered cubic structure. It has almost 24 isotopes. Out of 24 isotopes neptunium -237 is highly stable with half - life of 2.14 x 106 years. Its synthetic isotope neptunium 236 is also very stable with half life of 1.54 x 105 years. 


Neptunium Atomic Number and Electronic Configuration 

Atomic number of Neptunium is 93. It has 93 protons and 93 electrons. Its electronic configuration is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2 6p6 5f4 6d1 7s2 or it can be written as [Rn] 5f4 6d1 7s2 . It has 2 electrons in K – shell, 8 electrons in L – shell, 18 electrons in M – shell, 32 electrons in N - shell, 22 electrons in O shell, 9 electrons in P – shell and 2 electrons in Q - shell. 


Properties of Neptunium  

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Physical and Chemical Properties Physical and chemical properties of Neptunium are listed below –

  • Its atomic number is 93. It means it has 93 protons in its nucleus. 

  • Its atomic mass number is 237. 

  • It is a member of the actinide series and a radioactive element. 

  • It is a metal and has a silvery metallic appearance. 

  • It is a hard and ductile metal. 

  • It has orthorhombic crystal structure.

  • It is found as solid at STP.

  • It is paramagnetic.  

  • Melting point of neptunium is 639 .

  • Boiling point of neptunium is 4174 .

  • Its density is 19.38 g.cm-3.

  • It forms amphoteric oxides. 

  • Its common oxidation state is +5. 

  • It shows magnetic, electrical and optical properties as well.

  • According to the Pauling scale, its electronegativity is 1.36

  • Its allotrope – neptunium shows semi metallic properties. 

  • Neptunium based alloys exhibit very interesting magnetic behavior. 

  • It forms hydroxides by reaction with water. 

  • It is pyrophoric. 

  • Its ions react with oxygen and forms oxides such as NpO2, Np2O5 etc. 

  • Neptunium oxide reacts with hydrogen fluoride and hydrogen to give neptunium trifluoride and water. Reaction is given below –

NpO2 + ​1⁄2H2 + 3HF → NpF3 + 2H2O

Above reaction takes place at 400 .

When pure fluorine gas is passed through NpF3, it gives NpF4

  • Neptunium chloride can be formed by the reaction of carbon tetrachloride with neptunium oxide at 500 temperature. 

  • Its oxides with various oxidation states (+3 to +7) produces different colors in solution –

Np3+ - Violet

Np4+ - Yellow green

NpO2+ - Green (in acidic solution) and Yellow (in alkaline solution) 

NpO22+ - Reddish pink 

Np+7 – Green (in alkaline solution) and Brownish red (in acidic solution)

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Np ions in solution


Uses of Neptunium 

Neptunium, being a synthetic radioactive element, has no commercial uses at present but it is used to synthesize other elements such as plutonium – 238 etc. It is used as a precursor in plutonium – 238 production. Neptune – 237 is irradiated with neutrons to produce 238Pu. Reaction is given below –

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Plutonium – 238 is used in thermal generators, spacecrafts, military applications and as an – emitter. It is used in nuclear fuel as well. 

Neptunium – 237 is used for detection of high energy neutrons. It can be used in nuclear reactors and nuclear weapons. 


Harmful Effects 

It is a toxic element. Stable neptunium has a very long half - life, due to this it will be a major contributor to the total radiotoxicity in future. It is the most mobile actinide series element in the deep geological repository environment. It occurs in traces and does not have any biological role. Studies show that it is not absorbed by the digestive tract of animals and if it concentrates in the bones then it gets released slowly. 

Powdered neptunium metal possesses fire hazards as it is pyrophoric. Its small pieces can easily ignite spontaneously in air at room temperature. 

Neptunium: Summary In Tabular Form 

Neptunium 

Symbol 

Np

Discovered By 

American physicists Edwin McMillan and Philip H. Abelson at Berkeley Radiation Laboratory in 1940

Atomic number 

93

Standard atomic weight 

237

Crystal Structure 

Orthorhombic 

State at 20

Solid 

Melting point 

639

Boiling point 

4174

Period 

7th 

Series 

Actinide 

Block 

f

Electronic configuration 

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2 6p6 5f4 6d1 7s2 or [Rn] 5f4 6d1 7s2

Main properties 

Paramagnetic, radioactive  

Main use 

In production of plutonium 

Disadvantage 

Toxicity and fire hazards 


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