Lanthanide

Lanthanides [ lantanoi ː də ] (" Lanthanähnliche "; Greek: ending- ειδἠς ( - statutory ) "similar" ) is a group identify similar elements. Attributed to it are lanthanum and the 14 following the lanthanum in the Periodic Table elements cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. In the sense of the term lanthanum does not belong to the Lanthanähnlichen. Here the nomenclature of the IUPAC accepted but the practical use. The use of the old name lanthanides is still allowed. All lanthanide metals, and are also referred to as elements of the lanthanide series. They are part of the group of rare earth metals.

Occurrence

The lanthanides are also referred to as rare earth metals. This name is, however, insofar confusing because the elements of this group, with the exception of the unstable promethium are by no means as rare as it is suggested. For example, cerium in nature frequently than the arsenic or lead. On the earth's crust, they are involved in a mass fraction of 0.02%. There are a total of 14 elements of the sixth period, which can be regarded as a subgroup of the subgroup 3.

Due to their chemical similarity, the lanthanides occur in nature mostly socialized. Since the separation of individual lanthanides is difficult and its chemical properties are very similar, these elements are often under the ( unofficial ) chemical symbol Ln (not to be confused with La for lanthanum ) summarized. Many of them may from monazite (also known as secondary deposits - Monazitsande ) are obtained. The most common and economically important lanthanoidführenden minerals are:

• Monazite CePO4
• Xenotime YPO4
• Bastnäsit LnCO3F
• Parisit CaLn2 (CO3) 3F2
• Allanite Caln (Al, Fe 2 ) 3Si3O11OH
• Synchysite Caln (CO3) 2F
• Ankylit - (Ce) SrCe (CO3 ) 2 ( OH) · H2O
• Ankylit - ( La) Sr (La, Ce) [ OH | ( CO3) 2 ] · H2O
• Cerianite CeO2

In almost all minerals There is an accumulation of either the light (Ce) or the heavy lanthanides (Y behaves mineral chemically as a heavy lanthanide ). For example, monazite contains mainly Ce and La, while the content of the following lanthanides with atomic number decreases (hence the formula of monazite is also always given as CePO4 ). In xenotime (hence YPO4 ) one finds exactly the opposite case. This usually very effective fractionation is caused by the lanthanide contraction and the mineral to mineral different sizes available crystal lattice sites. Other mineral groups can sometimes high levels of lanthanides build into their structure (eg, zircon, garnet). Furthermore, the lanthanides are found on the moon in the form of so-called KREEP ores.

Properties

Physical Properties

The lanthanides are silvery shiny, relatively soft and reactive metals. Almost all have the typical for metals densest sphere packing. The hardness increases with increasing atomic number.

The lanthanides include as the actinides of the inner transition elements, or f -block elements, as in these series of f- orbitals are not completely filled with electrons.

The promethium isotopes are all unstable, ie radioactive.

Chemical Properties

Due to the similar structure of the elements, the lanthanides behave chemically as the elements of the third group of the periodic table scandium and yttrium, forming together with them, the group of rare earths. In the air they oxidize quickly and become matt. With water they react more or less rapidly to form hydrogen.

Starting from the 4f orbital of cerium is gradually filled up. It is finally fully staffed with lutetium with 14 electrons. Since the 4f orbitals are located deep inside the atoms, they take as opposed to the d orbitals of the other subgroup elements have little effect on the chemical behavior. The lanthanide elements are thus relatively similar in their chemical properties. They resemble each other so much that they were considered one and the same element even for the oxide upon the discovery of yttria in 1794. The same applies to the numerous components of the cerite earth. Common is the oxidation number of 3. In addition, some elements still occur in the oxidation states 2 and 4.

Colors of the lanthanide ions in aqueous solution

Lanthanide contraction

Due to the contraction of the lanthanoid atom radius increases in the number of cerium (183 pm ) to lutetium (172 pm ) is nearly constant from (exceptions are europium and ytterbium ). This is because the elements - starting from the atomic number - are the lanthanides, have already filled the 6s and 5p shells with electrons, however, the 4f shell not. The lanthanides now fill the 4f shell of electrons. In a simplified idea of the atom as consisting of spatially separated electron shells consisting closer to the core contained electron shell with charge carriers now fills a seen spatially. Besides the core fills naturally with the same number of protons as electrons are added to the 4f shell. Through the resulting stronger attraction between electrons and protons shrinks the atomic radius, while the atomic number increases.

This effect is actually not exceptional, as always decreases the radius when filling a tray within a period. However, arising out of this property some consequences:

• Due to the decreasing size separation by means of ion exchangers is easily possible. [NB 1]
• When Holmium is the radius of the Ln3 so small that it is almost the same of Y3 ; why you'll find most of yttrium with the " heavy earth" together
• Within a group, the transition elements of the 2nd and 3rd place have very similar properties.

Use

There are numerous examples of the use of the lanthanides:

• Cerium is the main ingredient in misch metal, which is used as " flint " of lighters, as well as oxide in self-cleaning ovens and as a catalyst in cracking. → Main article: cerium # Application
• Praseodymium: Located in yellow colored glass, such as welders goggles. → Main article: praseodymium # Application
• Neodymium: is mainly used for strong magnets. Is also part of the welder 's goggle lenses and is used in solid-state lasers in place of rubies. → Main article: Neodymium # Application
• Promethium: serves as a heat source in ( unmanned ) satellites and space probes. → Main article: promethium # Application
• Samarium: place as a permanent magnet application, such as in headphones. → Main article: Samarium # Application
• Europium: serves as a neutron absorber in nuclear power reactors, but also as an activator of the red phosphors in the TV tube. → Main article: europium # Application
• Gadolinium: is also found in the television tube as an activator of green phosphors. → Main article: gadolinium # Application
• Terbium: is used as a laser material. → Main article: terbium # Application
• Dysprosium: can be found as a neutron absorber in nuclear power reactors. → Main article: Dysprosium # Application
• Holmium: can only be found in alloys. In general, the lanthanides are often found in alloys, they make steel easier to process. → Main article: Holmium # Application
• Erbium: is contained in photographic filters. → Main article: Erbium # Application
• Thulium: used in nuclear power plants as a neutron absorber. → Main article: Thulium # Application
• Ytterbium: generates X-rays without electricity, eg in portable X-ray machines. → Main article: ytterbium # Application
• Lutetium: is a catalyst in cracking and polymerization. → Main article: Lutetium # Application