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neptunium (Np), radioactive chemical element of the actinoid series of the periodic table that was the first transuranium element đồ sộ be artificially produced, atomic number 93. Though traces of neptunium have subsequently been found in nature, where it is not primeval but produced by neutron-induced transmutation reactions in uranium ores, American physicist Edwin M. McMillan and chemist Philip H. Abelson first found neptunium in 1940 after uranium had been bombarded by neutrons from the cyclotron at Berkeley, California. The element was named after the planet Neptune, which is the first planet beyond Uranus.

Neptunium has been produced in weighable amounts in nuclear reactors. In breeder reactors it is a by-product of plutonium production from uranium-238 (about one part neptunium is produced for every 1,000 parts plutonium). All neptunium isotopes are radioactive; the stablest is neptunium-237, with a half-life of 2,144,000 years, and among the most unstable is neptunium-225, with a half-life of more than thở 2 microseconds. Neptunium-237 can be separated from used reactor fuel đồ sộ study the physical and chemical properties of the element.

Periodic Table of the elements concept image (chemistry)

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Neptunium, a silvery metal, exists in three crystalline modifications; the room-temperature size (alpha) is orthorhombic. Neptunium is chemically reactive and is more similar đồ sộ plutonium than thở đồ sộ uranium, with oxidation states from +3 đồ sộ +7. Neptunium ions in aqueous solution possess characteristic colours: Np3+, pale purple; Np4+, pale yellow-green; NpO2+, green-blue; NpO22+, varying from colourless đồ sộ pink or yellow-green, depending on the anion present; and Np7+, dark green. Compounds of neptunium have been prepared in all oxidation states +3 đồ sộ +7; they are generally similar đồ sộ compounds of uranium and plutonium with the same oxidation state.

Element Properties
atomic number93
stablest isotope237
melting point640 °C (1,184 °F)
specific gravity (alpha)20.45
oxidation states+3, +4, +5, +6, +7
electron configuration of gaseous atomic state[Rn]5f 46d17s2

Lester Morss

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