Molybdenum

Molybdenum is a chemical element; it has symbol Mo (from Neo-Latin molybdaenum) and atomic number 42. The name derived from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known throughout history, but the element was discovered (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm.

Molybdenum, ₄₂Mo

Molybdenum
Pronunciation	/məˈlɪbdənəm/ ​(mə-LIB-də-nəm)
Appearance	gray metallic
Standard atomic weight Ar°(Mo)
	95.95±0.01 95.95±0.01 (abridged)
Molybdenum in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Cr ↑ Mo ↓ W niobium ← molybdenum → technetium
Atomic number (Z)	42
Group	group 6
Period	period 5
Block	d-block
Electron configuration	[Kr] 4d5 5s1
Electrons per shell	2, 8, 18, 13, 1
Physical properties
Phase at STP	solid
Melting point	2896 K ​(2623 °C, ​4753 °F)
Boiling point	4912 K ​(4639 °C, ​8382 °F)
Density (at 20° C)	10.223 g/cm3
when liquid (at m.p.)	9.33 g/cm3
Heat of fusion	37.48 kJ/mol
Heat of vaporization	598 kJ/mol
Molar heat capacity	24.06 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 2742 2994 3312 3707 4212 4879
Atomic properties
Oxidation states	common: +4, +6 −4, −2, −1, 0, +1, +2, +3, +5
Electronegativity	Pauling scale: 2.16
Ionization energies	1st: 684.3 kJ/mol 2nd: 1560 kJ/mol 3rd: 2618 kJ/mol
Atomic radius	empirical: 139 pm
Covalent radius	154±5 pm
Other properties
Natural occurrence	primordial
Crystal structure	​body-centered cubic (bcc) (cI2)
Lattice constant	a = 314.71 pm (at 20 °C)
Thermal expansion	5.10×10−6/K (at 20 °C)
Thermal conductivity	138 W/(m⋅K)
Thermal diffusivity	54.3 mm2/s (at 300 K)
Electrical resistivity	53.4 nΩ⋅m (at 20 °C)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+89.0×10−6 cm3/mol (298 K)
Young's modulus	329 GPa
Shear modulus	126 GPa
Bulk modulus	230 GPa
Speed of sound thin rod	5400 m/s (at r.t.)
Poisson ratio	0.31
Mohs hardness	5.5
Vickers hardness	1400–2740 MPa
Brinell hardness	1370–2500 MPa
CAS Number	7439-98-7
History
Discovery	Carl Wilhelm Scheele (1778)
First isolation	Peter Jacob Hjelm (1781)
Isotopes of molybdenum v e
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 92Mo 14.7% stable 93Mo synth 4839 y ε 93Nb 94Mo 9.19% stable 95Mo 15.9% stable 96Mo 16.7% stable 97Mo 9.58% stable 98Mo 24.3% stable 99Mo synth 65.94 h β− 99mTc γ – 100Mo 9.74% 7.07×1018 y β−β− 100Ru
Category: Molybdenum view talk edit | references

Molybdenum does not occur naturally as a free metal on Earth; in its minerals, it is found only in oxidized states. The free element, a silvery metal with a grey cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of the world production of the element (about 80%) is used in steel alloys, including high-strength alloys and superalloys.

Most molybdenum compounds have low solubility in water. Heating molybdenum-bearing minerals under oxygen and water affords molybdate ion MoO²⁻
₄, which forms quite soluble salts. Industrially, molybdenum compounds (about 14% of world production of the element) are used as pigments and catalysts.

Molybdenum-bearing enzymes are by far the most common bacterial catalysts for breaking the chemical bond in atmospheric molecular nitrogen in the process of biological nitrogen fixation. At least 50 molybdenum enzymes are now known in bacteria, plants, and animals, although only bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Most nitrogenases contain an iron–molybdenum cofactor FeMoco, which is believed to contain either Mo(III) or Mo(IV). By contrast Mo(VI) and Mo(IV) are complexed with molybdopterin in all other molybdenum-bearing enzymes. Molybdenum is an essential element for all higher eukaryote organisms, including humans. A species of sponge, Theonella conica, is known for hyperaccumulation of molybdenum.