Science / Periodic Table of Elements / Lanthanum (La): Atomic number: 57, Atomic mass: 138.91 g.mol -1, Electronegativity: 1.1, Density: 6.18 g.cm-3 at 20Â°C, Melting point: 826 Â°C, Boiling point: 0.186 nm, Vanderwaals radius: 0.104 nm (+3), Isotopes: 7, Electronic shell: [ Xe ] 5d1 6s2, Energy of first ionisation: 539 kJ.mol -1, Energy of second ionisation: 1098 kJ.mol -1, Energy of third ionisation: 1840 kJ.mol -1, Standard potential: - 2.52 V ( La+3/ La ), Discovered by: Carl Mosander in 1839. Lanthanum is a soft, malleable, ductile, silver-white metal. It is chemically active, it is one of the most reactive of the rare-earth metals: it oxidizes rapidly in air and it reacts with water to form the hydroxide. Lanthanum is easily ignited, its salts are often very insoluble. Applications: Lanthanum is one of the rare chemicals, that can be found in houses in equipment such as colour televisions, fluorescent lamps, energy-saving lamps and glasses. All rare chemicals have comparable properties. La2O2 is used to make special optical glasses (infrared adsorbing glass, camera and telescope lenses). If added in small amounts it improves the malleability and resistence of steel. Lanthanum is used as the core material in carbon arc electrodes. Lanthanum salts are included in the zeolite catalysts used in petroleum refining because thay stabilize the zeolite at high temperatures. Lanthanium in the environment: Lanthanum can rarely be found in nature, as it occurs in very small amounts. It is anyway one of the more abundant rare-earch elements. Lanthanum is usually found only in two different kinds of ores. World production of lanthanum oxide in around 12.000 tonnes per year, and currently nown reseves of lanthanum are around 6 million tonnes. The use of lanthanum is still growing, due to the fact that it is suited to produce catalysers and to polish glass.