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Lanthanum

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                57               barium ← lanthanum → cerium
                 -
                ↑
                La
                ↓
                Ac

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                    Name, Symbol, Number lanthanum, La, 57
                                               Chemical series lanthanides
                                              Group, Period, Block 3, 6, f
                                                  Appearance silvery white
                                           Atomic mass 138.90547 (7) g/mol
                                     Electron configuration [Xe] 5d^1 6s^2
                                    Electrons per shell 2, 8, 18, 18, 9, 2
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 6.162 g·cm^−3
                                    Liquid density at m.p. 5.94 g·cm^−3
                                                     Melting point 1193  K
                                                     (920 ° C, 1688 ° F)
                                                      Boiling point 3737 K
                                                    (3464 ° C, 6267 ° F)
                                          Heat of fusion 6.20 kJ·mol^−1
                                   Heat of vaporization 402.1 kJ·mol^−1
                          Heat capacity (25 °C) 27.11 J·mol^−1·K^−1

   CAPTION: Vapor pressure (extrapolated)

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 2005 2208 2458 2772 3178 3726

                                                         Atomic properties
                                               Crystal structure hexagonal
                                                        Oxidation states 3
                                                    (strongly basic oxide)
                                    Electronegativity 1.10 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 538.1 kJ·mol^−1
                                                    2nd: 1067 kJ·mol^−1
                                                  3rd: 1850.3 kJ·mol^−1
                                                      Atomic radius 195 pm
                                                    Covalent radius 169 pm
                                                             Miscellaneous
                                                      Magnetic ordering  ?
                      Electrical resistivity ( r.t.) (α, poly) 615 nΩ·m
                       Thermal conductivity (300 K) 13.4 W·m^−1·K^−1
                                      Thermal expansion ( r.t.) (α, poly)
                                                           12.1 µm/(m·K)
                               Speed of sound (thin rod) (20 °C) 2475 m/s
                                        Young's modulus (α form) 36.6 GPa
                                          Shear modulus (α form) 14.3 GPa
                                           Bulk modulus (α form) 27.9 GPa
                                             Poisson ratio (α form) 0.280
                                                         Mohs hardness 2.5
                                                  Vickers hardness 491 MPa
                                                  Brinell hardness 363 MPa
                                             CAS registry number 7439-91-0
                                                         Selected isotopes

                CAPTION: Main article: Isotopes of lanthanum

                           iso     NA     half-life   DM  DE ( MeV)   DP
                          ^137La syn    60,000 yrs    ε   0.600     ^137Ba
                          ^138La 0.09%  1.05×10^11yrs ε   1.737     ^138Ba
                                                      β^- 1.044     ^138Ce
                          ^139La 99.91% La is stable with 82 neutrons

                                                                References

   Lanthanum ( IPA: /ˈlanθənəm/) is a chemical element in the periodic
   table that has the symbol La and atomic number 57.

Notable characteristics

   Lanthanum.
   Enlarge
   Lanthanum.

   Lanthanum is a silvery white metallic element belonging to group 3 of
   the periodic table and often considered to be one of the lanthanides.
   Found in some rare-earth minerals, usually in combination with cerium
   and other rare earth elements. Lanthanum is malleable, ductile, and
   soft enough to be cut with a knife. It is one of the most reactive of
   the rare-earth metals. The metal reacts directly with elemental carbon,
   nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with
   halogens. It oxidizes rapidly when exposed to air. Cold water attacks
   lanthanum slowly, while hot water attacks it much more rapidly.

Applications

   Uses of lanthanum:
     * Carbon lighting applications, especially by the motion picture
       industry for studio lighting and projection.
     * La[2]O[3] improves the alkali resistance of glass, and is used in
       making special optical glasses, such as:
          + Infrared absorbing glass.
          + Camera and telescope lenses, because of the high refractive
            index and low dispersion of rare-earth glasses.
     * Small amounts of lanthanum added to steel improves its
       malleability, resistance to impact and ductility.
     * Small amounts of lanthanum added to iron helps to produce nodular
       cast iron.
     * Small amounts of lanthanum added to molybdenum decreases the
       hardness of this metal and its sensitivity to temperature
       variations.
     * Mischmetal, a pyrophoric alloy used e.g. in lighter flints,
       contains 25% to 45% lanthanum.
     * Lanthanum oxide and the boride are used in electronic vacuum tubes
       as hot cathode materials with strong emissivity of electrons.
       Crystals of LaB[6] are used in high brightness, extended life,
       thermionic electron emission sources for scanning electron
       microscopes.
     * in Gas tungsten arc welding electrodes, as a substitute for
       radioactive thorium.
     * Hydrogen sponge alloys can contain lanthanum. These alloys are
       capable of storing up to 400 times their own volume of hydrogen gas
       in a reversible adsorption process.
     * Petroleum cracking catalysts.
     * Gas lantern mantles.
     * Glass and lapidary polishing compound.
     * La-Ba age dating of rocks and ores.
     * Lanthanum carbonate is used medically as a phosphate binder for the
       treatment of hyperphosphatemia. See details below under Biological
       Role.
     * Lanthanum nitrate is mainly applied in specialty glass, water
       treatment and catalyst.
     * Cerium activated Lanthanum bromide is the recent inorganic
       scintillator which has a combination of high light yield and the
       best energy resolution.

History

   Lanthanum was discovered in 1839 by Swedish chemist Carl Gustav
   Mosander, when he partially decomposed a sample of cerium nitrate by
   heating and treating the resulting salt with dilute nitric acid. From
   the resulting solution, he isolated a new rare earth he called lantana.
   Lanthanum was isolated in relatively pure form in 1923.

   The word lanthanum comes from the Greek λανθανω [lanthanō] = to lie
   hidden.

Biological Role

   Lanthanum has no known biological role.

   The element is not absorbed orally, and when injected its elimination
   is very slow. Lanthanum carbonate was approved as a medication
   (Fosrenol®, Shire Pharmaceuticals) to absorb excess phosphate in cases
   of end-stage renal failure. Some rare-earth chlorides, such as
   lanthanum chloride (LaCl[3]), are known to have anticoagulant
   properties.

   While Lanthanum has pharmacological effects on several receptors and
   ion channels its specificity for the GABA receptor is unique among
   divalent cations. Lanthanum acts at the same modulatory site on the
   GABAR as zinc- a known negative allosteric modulator. The Lanthanum
   cation La^3+ is a positive allosteric modulator at native and
   recombinant GABA receptors, increasing open channel time and decreasing
   desensitization in a subunit configuration dependant manner.

Occurrence

   Although lanthanum belongs to chemical elements group called rare earth
   metals, it is not rare at all. Lanthanum is available in relatively
   large quantities (32 ppm in Earth’s crust).

   Monazite (Ce, La, Th, Nd, Y)PO[4], and bastnasite (Ce, La, Y)CO[3]F,
   are principal ores in which lanthanum occurs in percentages up to 25 to
   38 percent.

Isotopes

   Naturally occurring lanthanum is composed of one stable (^139La) and
   one radioactive (^138La) isotope, with the stable isotope, ^139La,
   being the most abundant (99.91% natural abundance). 38 radioisotopes
   have been characterized with the most stable being ^138La with a
   half-life of 1.05×10^11 years, and ^137La with a half-life of 60,000
   years. All of the remaining radioactive isotopes have half-lives that
   are less than 24 hours and the majority of these have half lives that
   are less than 1 minute. This element also has 3 meta states.

   The isotopes of lanthanum range in atomic weight from 117 u (^117La) to
   155 u (^155La).

Precautions

   Lanthanum has a low to moderate level of toxicity, and should be
   handled with care. In animals, the injection of lanthanum solutions
   produces glycaemia, low blood pressure, degeneration of the spleen and
   hepatic alterations.
   Retrieved from " http://en.wikipedia.org/wiki/Lanthanum"
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