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 oxidises 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,
sulphur, and with halogens. It is a component of, misch metal (used for making
lighter flints).
•Name: Lanthanum
•Symbol: La
•Atomic number: 57
•Atomic weight: 138.90547 (7) [see note g]
•Standard state: solid at 298 K
•CAS Registry ID: 7439-91-0
•Group in periodic table:
•Group name: Lanthanoid
•Period in periodic table: 6 (lanthanoid)
•Block in periodic table: f-block
•Color: silvery white
•Classification: Metallic
Historical information
Lanthanum was discovered by Carl Gustaf Mosander at 1839 in Sweden, when he recognized the element lanthanum in impure cerium nitrate. Origin of name: from the Greek word "lanthanein" meaning "to lie hidden". His extraction resulted in the oxide lanthana (La2O3). A number of other lanthanides (rare-earths) were later discovered by identification of the impurities in yttrium and cerium compounds.
Physical properties
•Melting point: 1193 [or 920 °C (1688 °F)] K
•Boiling point: 3743 [or 3470 °C (6278 °F)] K
•Density of solid: 6146 kg m-3
Orbital properties
•Ground state electron configuration: [Xe].5d1.6s2
•Shell structure: 2.8.18.18.9.2
•Term symbol: 2D3/2
Isolation
Llanthanum metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to separate it from as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.
For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography.
Pure lanthanum is available through the reduction of LaF3 with calcium metal.
2LaF3 + 3Ca → 2La + 3CaF2
This would work for the other calcium halides as well but the product CaF2 is easier to handle under the reaction conditions (heat to 50°C above the melting point of the element in an argon atmosphere). Excess calcium is removed from the reaction mixture under vacuum.
•Name: Lanthanum
•Symbol: La
•Atomic number: 57
•Atomic weight: 138.90547 (7) [see note g]
•Standard state: solid at 298 K
•CAS Registry ID: 7439-91-0
•Group in periodic table:
•Group name: Lanthanoid
•Period in periodic table: 6 (lanthanoid)
•Block in periodic table: f-block
•Color: silvery white
•Classification: Metallic
Historical information
Lanthanum was discovered by Carl Gustaf Mosander at 1839 in Sweden, when he recognized the element lanthanum in impure cerium nitrate. Origin of name: from the Greek word "lanthanein" meaning "to lie hidden". His extraction resulted in the oxide lanthana (La2O3). A number of other lanthanides (rare-earths) were later discovered by identification of the impurities in yttrium and cerium compounds.
Physical properties
•Melting point: 1193 [or 920 °C (1688 °F)] K
•Boiling point: 3743 [or 3470 °C (6278 °F)] K
•Density of solid: 6146 kg m-3
Orbital properties
•Ground state electron configuration: [Xe].5d1.6s2
•Shell structure: 2.8.18.18.9.2
•Term symbol: 2D3/2
Isolation
Llanthanum metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to separate it from as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.
For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography.
Pure lanthanum is available through the reduction of LaF3 with calcium metal.
2LaF3 + 3Ca → 2La + 3CaF2
This would work for the other calcium halides as well but the product CaF2 is easier to handle under the reaction conditions (heat to 50°C above the melting point of the element in an argon atmosphere). Excess calcium is removed from the reaction mixture under vacuum.
No comments:
Post a Comment