Molybdenum

Molybdenum,  ₄₂Mo

General properties
Pronunciation	/məˈlɪbdɪnəm/ ​(mə-LIB-din-əm)
Appearance	gray metallic
Standard atomic weight (Ar, standard)	7001959500000000000♠95.95(1)
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
Element category	transition metal
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 (near r.t.)	10.28 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	6, 5, 4, 3, 2, 1, −1, −2, −4 ​(a strongly acidic oxide)
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
Spectral lines
Miscellanea
Crystal structure	​body-centered cubic (bcc)
Speed of sound thin rod	5400 m/s (at r.t.)
Thermal expansion	4.8 µm/(m·K) (at 25 °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
Magnetic susceptibility	+89.0·10−6 cm3/mol (298 K)
Young's modulus	329 GPa
Shear modulus	126 GPa
Bulk modulus	230 GPa
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)
Main isotopes of molybdenum
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 92Mo 14.65% stable 93Mo syn 4×103 y ε 93Nb 94Mo 9.19% stable 95Mo 15.87% stable 96Mo 16.67% stable 97Mo 9.58% stable 98Mo 24.29% stable 99Mo syn 65.94 h β− 99mTc γ – 100Mo 9.74% 7.8×1018 y β−β− 100Ru
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Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, 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 does not occur naturally as a free metal on Earth; it is found only in various oxidation states in minerals. The free element, a silvery metal with a gray cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of 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, but when molybdenum-bearing minerals contact oxygen and water, the resulting molybdate ion MoO²⁻
₄ is quite soluble. Industrially, molybdenum compounds (about 14% of world production of the element) are used in high-pressure and high-temperature applications 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. These nitrogenases contain molybdenum in a form different from other molybdenum enzymes, which all contain fully oxidized molybdenum in a molybdenum cofactor. These various molybdenum cofactor enzymes are vital to the organisms, and molybdenum is an essential element for life in all higher eukaryote organisms, though not in all bacteria.