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Lanthanum - La General Information Discovery Lanthanum was discovered by C.G. Mosander in 1839 in Stockholm, Sweden. Appearance Lanthanum is a silvery-white metal which can be cut with a knife. It is ductile, malleable and tarnishes in air. Source Lanthanum is found in 'rare earth' minerals, principally monazite (25% lanthanum) and bastnaesite (38% lanthanum). Ion-exchange and solvent extraction techniques enable the 'rare earth' elements to be isolated from the mineral, and lanthanum is usually obtained by reducing the anhydrous fluoride with calcium. Uses 'Rare earth' compounds containing lanthanum are used extensively in carbon lighting applications, such as studio lighting and cinema projection. Lanthanum(III) oxide is used in making special optical glasses, as it improves the alkali resistance of glass. The ion lanthanum3+ is used as a biological tracer for Ca2+, and radioactive lanthanum has been tested for use in treating cancer. Biological Role Lanthanum has no known biological role, but both the element and its compounds are moderately toxic. General Information Lanthanum is one of the most reactive of the 'rare earth' metals. It oxidises rapidly when exposed to the air, and burns easily. It is attacked slowly by cold water, and rapidly by hot water. It reacts directly with carbon, nitrogen, phosphorus, sulfur, the halogens and some other elements. At room temperature, the structure of lanthanum is hexagonal. This changes to face-centred cubic at 310K, and to body-centred cubic at 865K. |
| Physical Information | |||
| Atomic Number | 57 | ||
| Relative Atomic Mass (12C=12.000) | 138.91 | ||
| Melting Point/K | 1194 | ||
| Boiling Point/K | 3730 | ||
| Density/kg m-3 | 6145 (298K) | ||
| Ground State Electron Configuration | [Xe]5d16s2 | ||
| Electron Affinity(M-M-)/kJ mol-1 | -53 |
| Key Isotopes | ||||||
| nuclide | 138La | 139La | 140La | |||
| atomic mass | 137.9 | 138.9 | ||||
| natural abundance | 0.09% | 99.91% | 0% | |||
| half-life | stable | stable | 40.22 h |
| Other Information | ||
| Enthalpy of Fusion/kJ mol-1 | 10.04 | |
| Enthalpy of Vaporisation/kJ mol-1 | 402.1 | |
| Oxidation States | ||
| La+3 | ||
| Ionisation Energies/kJ mol-1 | ||
| M - M+ | 538.1 | |
| M+ - M2+ | 1067 | |
| M2+ - M3+ | 1850 | |
| M3+ - M4+ | 4819 | |
| M4+ - M5+ | 6400 | |
| M5+ - M6+ | 7600 | |
| M6+ - M7+ | 9600 | |
| M7+ - M8+ | 11000 | |
| M8+ - M9+ | 12400 | |
| M9+ - M10+ | 15900 | |
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