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Lanthanum was first found by the Swedish chemist Carl Gustav Mosander in 1839 as an impurity in cerium nitrate – hence the name lanthanum, from the Ancient Greek λανθάνειν (lanthanein), meaning "to lie hidden".Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead.However, scandium still shows many differences from lutetium because it is even smaller, and in any case the similarity of yttrium is more generally to all of the late lanthanides from gadolinium onward, especially holmium which has almost the same ionic radius.The trends going down from scandium and yttrium to lanthanum tend to be more similar to those going down groups 1 and 2 in the periodic table, while those going down from scandium and yttrium to lutetium tend to be more similar to those in the early transition metals.Thus it is only very weakly paramagnetic, unlike the strongly paramagnetic later lanthanides (with the exceptions of the last two, ytterbium and lutetium, where the 4f shell is completely full).Furthermore, since the melting points of the trivalent lanthanides are related to the extent of hybridisation of the 6s, 5d, and 4f electrons, lanthanum has the second-lowest (after cerium) melting point among all the lanthanides: 920 °C.Since Sc, it has been argued that lanthanum and the rest of group 3 should be considered at best atypical transition metals, as their chemistry is focused on the predominantly ionic 3 state and they have a low ability to form coordination compounds or organometallic compounds.Indeed, lanthanum is a strongly electropositive metal, comparable to calcium in electropositivity.) at high temperature.
It is also sometimes considered the first element of the 6th-period transition metals and is traditionally counted among the rare earth elements. Lanthanum has no biological role in humans but is essential to some bacteria.Like most of the lanthanides, lanthanum has a hexagonal crystal structure at room temperature.At 310 °C, lanthanum changes to a face-centered cubic structure, and at 865 °C, it changes to a body-centered cubic structure.The lanthanides become harder as the series is traversed: as expected, lanthanum is a soft metal.Lanthanum has a relatively high resistivity of 615 nΩm at room temperature; in comparison, the value for the good conductor aluminium is only 26.50 nΩm.