| Lanthanum
CAS: 7439-91-0 Description: Soft, silvery-white metal Classification: Rare Earth Date of Discovery: 1839 Discoverer: Carl Mosander Name Origin: Greek lanthanein "to lie hidden" |
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Atomic Number: 57
Number of Neutrons: 82 Atomic Mass: 138.9055(2) amu Melting Point: 918 °C Boiling Point: 3464 °C Density @ 25 °C: 6.145 g/cm3 Atomic volume: 20.73 cm3/mol Electrical resistivity: 0.0126 10-6/cm 
Thermal conductivity: 0.135 W/cmK Enthalpy of atomization: 431 kJ/mol (est.) Enthalpy of vaporization: 414.0 kJ/mol Enthalpy of fusion: 6.20 kJ/mol Specific heat capacity: 0.19 J/gK |
Energy levels: 2-8-18-18-9-2
Electron configuration: [Xe]5d16s2 Crystal Structure: Hexagonal (below 310 °C) Atomic radius: 2.74 Å Covalent radius: 1.69 Å Oxidation States: +3 Electronegativity, Pauling: 1.10 Electron affinity: 0.5 eV First ionization energy: 5.58 eV 2nd ionization energy: 11.059 eV 3rd ionization energy: 19.174 eV Polarizability: 31.1 10-24cm3 |
| Isotope | Natural Abundance | Atomic Mass | Half-life | Decay Mode | Spin |
| 120La | 119.938 | 2.8 s | EC,  + |
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| 122La | 121.931 | 9 s | EC, + |
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| 123La | 122.9262 | 17 s | EC | ||
| 124La | 123.9245 | 30 s | EC | (7+) | |
| 125La | 124.9207 | 1.2 m | +, EC |
11/2- | |
| 126La | 125.9194 | 1.0 m | +, EC |
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| 127La | 126.9162 | 3.8 m | +, EC |
3/2+ | |
| 128La | 127.9155 | 5.0 m | +; EC |
(5-) | |
| 129mLa | 0.56 s | IT | (11/2-) | ||
| 129La | 128.91267 | 11.6 m | - |
3/2+ | |
| 130La | 129.9123 | 8.7 m | +; EC |
3+ | |
| 131La | 130.9101 | 59 m | +; EC |
3/2+ | |
| 132mLa | 24 m | IT; + |
6- | ||
| 132La | 131.91011 | 4.8 h | +; EC |
2- | |
| 133La | 132.9084 | 3.91 h | +; EC |
5/2+ | |
| 134La | 133.90849 | 6.5 m | +; EC |
1+ | |
| 135La | 134.90697 | 19.5 h | EC | 5/2+ | |
| 136La | 135.9077 | 9.87 m | +; EC |
1+ | |
| 137La | 136.90647 | 60000 y | EC | 7/2+ | |
| 138La | 0.0902(2) | 137.907107 | 1.06 x 1011 y | 5+ | |
| 139La | 99.9098(2) | 138.906349 | Stable | 7/2+ | |
| 140La | 139.909473 | 1.678 d | - |
3- | |
| 141La | 140.910958 | 3.90 h | - |
7/2+ | |
| 142La | 141.91408 | 1.54 h | - |
2- | |
| 143La | 142.91606 | 14.1 m | - |
7/2- | |
| 144La | 143.9196 | 40.7 s | - |
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| 145La | 144.9217 | 24 s | - |
3/2+ | |
| 146mLa | 10.0 s | - |
(6) | ||
| 146La | 145.9258 | 6.3 s | - |
(2-) | |
| 147La | 146.9278 | 4.02 s | - |
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| 148La | 147.9322 | 1.1 s | - |
2- | |
| 149La | 148.9342 | 1.10 s | - |
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Mosander in 1839 extracted a new earth lanthana, from impure cerium nitrate, and recognized the new element. Lanthanum is found in rare-earth minerals such as cerite, monazite [(La,Ce,Nd)PO4], allanite [Ca(La,Ce)(Fe2+,Mn2+)(Al,Fe3+)2(SiO4)(Si2O7)O(OH)], and bastnasite [(La,Ce)(CO3)F]. Monazite and bastnasite are principal ores in which lanthanum occurs in percentages up to 25 and 38%, respectively. Misch metal, used in making lighter flints, contains about 25% lanthanum. Lanthanum was isolated in relatively pure form in 1923. Iron-exchange and solvent extraction techniques have led to much easier isolation of the so-called "rare-earth" elements. The availability of lanthanum and other rare earths has improved greatly in recent years. The metal can be produced by reducing the anhydrous fluoride with calcium. Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. It oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, and hot water attacks it much more rapidly. The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens. At 310 °C, lanthanum changes from a hexagonal to a face-centered cubic structure, and at 865 °C it again transforms into a body-centered cubic structure. Natural lanthanum is mixture of two isotopes, one of which is stable and one of which is radioactive with a very long half-life. Twenty-nine other radioactive isotopes are recognized. Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25% of the rare-earth compounds produced. La2O3 improves the alkali resistance of glass, and is used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron. There is current interest in hydrogen sponge alloys containing lanthanum. These alloys take up to 400 times their own volume of hydrogen gas, and the process is reversible. Heat energy is released every time they do so; therefore these alloys have possibilities in energy conservation systems. Lanthanum and its compounds have a low to moderate acute toxicity rating; therefore, care should be taken in handling them.
LINKS: Electronic Structure of Lanthanum Hydrides with Switchable Opitcal Properties Information, data sheet and standard forms Lanthanum Hexaboride Cathodes Measurement of the Electron Affinity of Lanthanum Mobility of Ions in Lanthanum Fluoride Nanoclusters Return
Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998. |
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