 | ||||||||||||||||||||||||||||
| Lanthanum | ||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Pronunciation | /ˈlænθənəm/ | |||||||||||||||||||||||||||
| Appearance | silvery white | |||||||||||||||||||||||||||
| Standard atomic weight Ar°(La) | ||||||||||||||||||||||||||||
| Lanthanum in the periodic table | ||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||
| Atomic number (Z) | 57 | |||||||||||||||||||||||||||
| Group | f-block groups (no number) | |||||||||||||||||||||||||||
| Period | period 6 | |||||||||||||||||||||||||||
| Block | f-block | |||||||||||||||||||||||||||
| Electron configuration | [Xe] 5d1 6s2 | |||||||||||||||||||||||||||
| Electrons per shell | 2, 8, 18, 18, 9, 2 | |||||||||||||||||||||||||||
| Physical properties | ||||||||||||||||||||||||||||
| Phase at STP | solid | |||||||||||||||||||||||||||
| Melting point | 1193 K (920 °C, 1688 °F) | |||||||||||||||||||||||||||
| Boiling point | 3737 K (3464 °C, 6267 °F) | |||||||||||||||||||||||||||
| Density (at 20° C) | 6.145 g/cm3 [3] | |||||||||||||||||||||||||||
| when liquid (at m.p.) | 5.94 g/cm3 | |||||||||||||||||||||||||||
| Heat of fusion | 6.20 kJ/mol | |||||||||||||||||||||||||||
| Heat of vaporization | 400 kJ/mol | |||||||||||||||||||||||||||
| Molar heat capacity | 27.11 J/(mol·K) | |||||||||||||||||||||||||||
Vapor pressure (extrapolated)
| ||||||||||||||||||||||||||||
| Atomic properties | ||||||||||||||||||||||||||||
| Oxidation states | common: +3 0,[4] +1,[5] +2[6] | |||||||||||||||||||||||||||
| Electronegativity | Pauling scale: 1.10 | |||||||||||||||||||||||||||
| Ionization energies |
| |||||||||||||||||||||||||||
| Atomic radius | empirical: 187 pm | |||||||||||||||||||||||||||
| Covalent radius | 207±8 pm | |||||||||||||||||||||||||||
 | ||||||||||||||||||||||||||||
| Other properties | ||||||||||||||||||||||||||||
| Natural occurrence | primordial | |||||||||||||||||||||||||||
| Crystal structure | α form: double hexagonal close-packed (dhcp) (hP4) | |||||||||||||||||||||||||||
| Lattice constants |  c = 1.2171 nm (at 20 °C)[3] | |||||||||||||||||||||||||||
| Thermal expansion | 5.1×10−6/K (at 20 °C)[3][a] | |||||||||||||||||||||||||||
| Thermal conductivity | 13.4 W/(m⋅K) | |||||||||||||||||||||||||||
| Electrical resistivity | α, poly: 615 nΩ⋅m (at r.t.) | |||||||||||||||||||||||||||
| Magnetic ordering | paramagnetic[7] | |||||||||||||||||||||||||||
| Molar magnetic susceptibility | +118.0×10−6 cm3/mol (298 K)[8] | |||||||||||||||||||||||||||
| Young's modulus | α form: 36.6 GPa | |||||||||||||||||||||||||||
| Shear modulus | α form: 14.3 GPa | |||||||||||||||||||||||||||
| Bulk modulus | α form: 27.9 GPa | |||||||||||||||||||||||||||
| Speed of sound thin rod | 2475 m/s (at 20 °C) | |||||||||||||||||||||||||||
| Poisson ratio | α form: 0.280 | |||||||||||||||||||||||||||
| Mohs hardness | 2.5 | |||||||||||||||||||||||||||
| Vickers hardness | 360–1750 MPa | |||||||||||||||||||||||||||
| Brinell hardness | 350–400 MPa | |||||||||||||||||||||||||||
| CAS Number | 7439-91-0 | |||||||||||||||||||||||||||
| History | ||||||||||||||||||||||||||||
| Discovery | Carl Gustaf Mosander (1838) | |||||||||||||||||||||||||||
| Isotopes of lanthanum | ||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||
Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. Lanthanum is traditionally counted among the rare earth elements. Like most other rare earth elements, its usual oxidation state is +3, although some compounds are known with an oxidation state of +2. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.
Lanthanum usually occurs together with cerium and the other rare earth elements. Lanthanum was first found by the Swedish chemist Carl Gustaf Mosander in 1839 as an impurity in cerium nitrate – hence the name lanthanum, from the ancient Greek λανθάνειν (lanthanein), meaning 'to lie hidden'. Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead. In minerals such as monazite and bastnäsite, lanthanum composes about a quarter of the lanthanide content.[10] It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923.
Lanthanum compounds have numerous applications including catalysts, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes, scintillators, and gas tungsten arc welding electrodes. Lanthanum carbonate is used as a phosphate binder to treat high levels of phosphate in the blood accompanied by kidney failure.
- ^ "Standard Atomic Weights: Lanthanum". CIAAW. 2005.
- ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
- ^ a b c d Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
- ^ Yttrium and all lanthanides except Ce and Pm have been observed in the oxidation state 0 in bis(1,3,5-tri-t-butylbenzene) complexes, see Cloke, F. Geoffrey N. (1993). "Zero Oxidation State Compounds of Scandium, Yttrium, and the Lanthanides". Chem. Soc. Rev. 22: 17–24. doi:10.1039/CS9932200017. and Arnold, Polly L.; Petrukhina, Marina A.; Bochenkov, Vladimir E.; Shabatina, Tatyana I.; Zagorskii, Vyacheslav V.; Cloke (15 December 2003). "Arene complexation of Sm, Eu, Tm and Yb atoms: a variable temperature spectroscopic investigation". Journal of Organometallic Chemistry. 688 (1–2): 49–55. doi:10.1016/j.jorganchem.2003.08.028.
- ^ La(I), Pr(I), Tb(I), Tm(I), and Yb(I) have been observed in MB8− clusters; see Li, Wan-Lu; Chen, Teng-Teng; Chen, Wei-Jia; Li, Jun; Wang, Lai-Sheng (2021). "Monovalent lanthanide(I) in borozene complexes". Nature Communications. 12 (1): 6467. doi:10.1038/s41467-021-26785-9. PMC 8578558. PMID 34753931.
- ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.
- ^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
- ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
- ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
- ^ "Monazite-(Ce) Mineral Data". Webmineral. Retrieved 10 July 2016.
Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).