Symbol	La
Atomnummer	57
Gruppe	3 (Scandiumgruppe)
Periode	6
Blok	d
Klassifikation	Lanthanider

Udseende	Silvery white
Farve	Sølv

Antal protoner	57 p+
Antal neutroner	82 n0
Antal elektroner	57 e-

Fra Wikipedia, den gratis encyklopædiLanthan (af græsk; λανθανω [lanthanō] "det der ligger skjult") er det 57. grundstof i det periodiske system: Det har det kemiske symbol La, og under normale temperatur- og trykforhold optræder stoffet som et sølvhvidt metal, der er blødt nok til at man kan skære i det med en kniv. Lanthan er et af de mest reaktive stoffer blandt de sjældne jordarter, og danner af sig selv kemiske forbindelser med kulstof, kvælstof, bor, selen, silicium, fosfor, svovl og med alle halogenerne — på grund af denne reaktionsvillighed iltes ("ruster") lanthan hurtigt hvis det kommer i kontakt med atmosfærisk luft. Lanthan angribes også af vand, men her spiller temperaturen en væsentlig rolle for reaktionshastigheden; i varmt vand forløber denne reaktion meget hurtigere end i koldt vand.

Fase ved STP	Fast
Massefylde	6.162 g/cm3
Atommasse	138.905 u

Smeltepunkt	1193 K 919.85 °C 1687.73 °F
Kogepunkt	3737 K 3463.85 °C 6266.93 °F
Fordampningsvarme	399.57 kJ/mol

Elektronegativitet (Pauling Scale)	1.1
Elektronaffinitet	53 kJ/mol
Oxidationstrin	0, +1, +2, +3 (a strongly basic oxide)
Ioniseringsenergier	538.1 kJ/mol 1067 kJ/mol 1850.3 kJ/mol 4819 kJ/mol 5940 kJ/mol

Elektronkonfiguration Kortfattet konfiguration	[Xe] 5d1 6s2
Elektronkonfiguration Fuld konfiguration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 5d1 6s2
Elektronkonfigurationsdiagram	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 5d1 6s2
Elektroner pr. Skal	2, 8, 18, 18, 9, 2
Valenselektroner	2
Valency-elektroner	3
Bohrs atommodel	Figur: Skaldiagram af Lanthan (La) atom.
Orbital diagram	1s 2s 2p 3s 3p 3d 4s 4p 4d 5s 5p 5d 6s

Opdaget	Carl Gustaf Mosander (1838)
Navngivet af	Carl Gustaf Mosander
Opdagelse af lanthan In 1751, the Swedish mineralogist Axel Fredrik Cronstedt discovered a heavy mineral from the mine at Bastnäs, later named cerite. Thirty years later, the fifteen-year-old Wilhelm Hisinger, from the family owning the mine, sent a sample of it to Carl Scheele, who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral with Jöns Jacob Berzelius and isolated a new oxide which they named ceria after the dwarf planet Ceres, which had been discovered two years earlier. Ceria was simultaneously independently isolated in Germany by Martin Heinrich Klaproth. Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist Carl Gustaf Mosander, who lived in the same house as Berzelius and studied under him: he separated out two other oxides which he named lanthana and didymia. He partially decomposed a sample of cerium nitrate by roasting it in air and then treating the resulting oxide with dilute nitric acid. That same year, Axel Erdmann, a student also at the Karolinska Institute, discovered lanthanum in a new mineral from Låven island located in a Norwegian fjord. Finally, Mosander explained his delay, saying that he had extracted a second element from cerium, and this he called didymium. Although he didn't realise it, didymium too was a mixture, and in 1885 it was separated into praseodymium and neodymium. Since lanthanum's properties differed only slightly from those of cerium, and occurred along with it in its salts, he named it from the Ancient Greek λανθάνειν [lanthanein] (lit. to lie hidden). Relatively pure lanthanum metal was first isolated in 1923.

CAS Number	7439-91-0
ChemSpider ID	22369
EC number	231-099-0
PubChem CID Number	23926