Lanthanum Element Facts / Chemistry

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57 La 138.9055 Lanthanum

Name: Lanthanum
Type: Transition Metal
Density @ 293 K: 6.16 g/cm³

Discovery of Lanthanum
Lanthanum was discovered in 1839 by Carl G. Mosander in the mineral cerite.

Ceria (cerium oxide) had already been discovered in 1803 by Jöns J. Berzelius in the mineral cerite. Mosander, who had been one of Berzelius's students, suspected that ceria was an impure oxide containing other rare earths. ⁽¹⁾

Mosander took finely powdered cerium nitrate and added cold dilute nitric acid. Some of the cerium nitrate powder dissolved in the acid indicating a new earth might be present. The new oxide was more basic than ceria (cerium oxide) and, unlike ceria, dissolved in the acid. Mosander separated the solution from the precipitate using sodium oxalate and heat. He obtained a pale brick colored oxide of the new rare earth. ^(1a)

The name lanthana for the new oxide was suggested by his friend Berzelius.

The name comes from the Greek word 'lanthano,' meaning to be hidden.

Axel Erdmann discovered lanthanum independently in the same year as Mosander in a newly found Norwegian mineral. Erdmann called the new mineral mosandrite, in honor of Mosander. ⁽²⁾

Mosander obtained impure metallic lanthanum from the chloride. ^(1a)

Pure lanthanum metal was first produced in 1923 by electrolysis of the fused halides by H. Kremers and R. Stevens.

Mosander continued studying lanthana and in 1841 announced the discovery of another rare earth contained in it. He named it 'didymium' because it seemed to be 'an inseparable twin brother of lanthanum.' ^(2a)

Symbol: La
Atomic weight: 138.9055
Atomic volume: 22.5 cm³/mol

State (s, l, g): solid
Melting point: 1193.2 K   (920 ^oC)

Boiling point: 3733 K   (3460 ^oC)

Specific heat capacity: 0.19 J g^-1 K^-1
Heat of fusion: 6.20 kJ mol^-1
1^st ionization energy: 538.1 kJ mol^-1
3^rd ionization energy: 1850 kJ mol^-1

Heat of atomization: 414 kJ mol^-1
Heat of vaporization : 400 kJ mol^-1
2^nd ionization energy: 1067 kJ mol^-1
Electron affinity: 50 kJ mol^-1

Shells: 2,8,18,18,9,2
Minimum oxidation number: 0
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 1.1

Electron configuration: [Kr] 5d¹ 6s²
Maximum oxidation number: 3
Max. common oxidation no.: 3
Polarizability volume: 31.1 ų

Structure: hcp: hexagonal close packed
Hardness: 2.5 mohs

Color: silvery-white


Harmful effects:
Lanthanum and its compounds are considered to be moderately toxic.

Characteristics:
Lanthanum is a silvery-white soft metal, which can be cut with a knife.

It is ductile, malleable and exposed surfaces tarnish rapidly in air forming the oxide.

Lanthanum reacts with water to form lanthanum hydroxide plus hydrogen gas.

Lanthanum is chemically reactive and forms compounds with carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with the halogens.

Lanthanum usually exists as a trivalent ion, La³⁺, in its compounds.

Uses:
Lanthanum is used in large quantities in nickel metal hydride (NiMH) rechargeable batteries for hybrid automobiles. The negative electrode (cathode) in NiMH batteries is a mixture of metal hydrides - one of which is typically lanthanum hydride. The active material at the cathode is hydrogen, which is stored in the metal hydride structure. The metal hydride can, depending on its composition, hold between 1% and 7% hydrogen by weight. ⁽³⁾ A Toyota Prius battery requires about 10 kg of lanthanum. ⁽⁴⁾

Lanthanum is used as a petroleum cracking catalyst, catalyzing the splitting of long chain hydrocarbons into shorter chained species.

Lanthanum is used as an additive to make nodular cast iron and as an additive in steel.

Flame lighter flints use misch metal (a rare earth alloy) containing lanthanum to produce sparks by friction.

Lanthanum is used in hydrogen sponge alloys, which take up to 400 times their own volume of hydrogen gas.

Lanthanum is also used to make night vision goggles (infrared-absorbing glass).

High quality camera and telescope lenses contain lanthanum oxide (La₂O₃) making use of its high refractive index and low dispersion.

Lanthanum carbonate is used to reduce blood levels of phosphate in patients with kidney disease. ⁽⁵⁾

Lanthanum compounds are also used in some pool products to reduce the level of phosphate nutrients that algae feed on.

Reaction with air: vigorous, w/ht ⇒ La₂O₃
Reaction with 15 M HNO₃: mild, ⇒ La(NO₃)₃
Oxide(s): La₂O₃
Hydride(s): LaH₂, LaH₃

Reaction with 6 M HCl: mild, ⇒ H₂, LaCl₃
Reaction with 6 M NaOH: none
Chloride(s): LaCl₃

Atomic radius: 195 pm
Ionic radius (2+ ion): pm
Ionic radius (2- ion): pm

Ionic radius (1+ ion): pm
Ionic radius (3+ ion): 117.2 pm
Ionic radius (1- ion): pm

Thermal conductivity: 13.4 W m^-1 K^-1

Electrical conductivity: 1.9 x 10⁶ S m^-1