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Chemistry Inorganic Chemistry Main Group Elements Lanthanides

Lanthanides 0

The arrangement of all elements is based on the electronic configuration of theelements and the "long form" of the Periodic table or the Modern Periodic table isdesigned keeping this factor in mind.

Accordingly the elements in which the f-block is getting filled are kept at the bottomportion of the periodic table and are called f-block elements or Lanthanides in the 6thperiod and an incomplete 7th period called Actinides.

The lanthanides are a series of fifteen metal elements that are next to each other nearthe bottom of the periodic table. The name of the series comes from lanthanum, theelement that marks the beginning of the series. All members of the series have similarchemical properties. In nature, they are found together in the same minerals and it isdifficult to separate them into individual elements.

Atomic Number Name Symbol57 lanthanum La58 cerium Ce59 praseodymium Pr60 neodymium Nd61 promethium Pm62 samarium Sm63 europium Eu64 gadolinium Gd65 terbium Tb66 dysprosium Dy67 holmium Ho68 erbium Er

69 thulium Tm70 ytterbium Yb71 lutetium Lu

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Lanthanides Definition

Properties of Lanthanides

Characteristics ofLanthanides

Uses of Lanthanides

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Lanthanides

Lanthanides Definition Back to Top

Properties of Lanthanides Back to Top

Lanthanides can be defined as those elements in which the 4f-block gets

filled gradually from 4f1(Cerium) to 4f14(Lutetium) where the filling up ofelectrons take place at n-2 orbit (second orbit below the outermost orbit).

Lanthanides have the uncharacteristic feature of having almost similar properties.They were initially known as rare earth metals but now they are mostly termed as innertransition elements. An alternative term for lanthanide is "rare earth". The word earth,once used by chemists for compounds, is now called oxides. A compound is formedwhen atoms of different elements bond together during a chemical reaction. Rare earthwas the term used for the oxides of lanthanide elements to distinguish them frombetter known earths.

The properties of Lanthanides can be classified as general (Physical) and ChemicalProperties.

Solubility

Most of the salts of lanthanides are soluble in water as they show water ofcrystallization. This can be attributed to the availability of empty spaces in d and forbitals. Most of the salts of lanthanides resemble the salts of group 2 elements likeCa, Ba in their solubilities. Flourides, oxalates and carbonates are almost insolublewhile chlorides and nitrates are soluble.

However, unlike the sulphates of Ca and Ba which are insoluble, the lanthanidesulphates are soluble in water. With ammonium of I group metals like Na and Klanthanides form double salts which can be crystallized well. For example, Na2SO4Ln2(SO4)3.8H2O. This property helps in the separation of lanthanides from one anotherdue to the varying solubility of these double salts.

Colored Compounds

Like the transition elements (d block elements) the f-block lanthanides in their +3oxidation state also produce colors in crystalline as well as in solution forms. Thedepth of the color increases with the increase in the number of unpaired electrons inthe f orbital. The compounds in which the lanthanides are in some other oxidation stateand iso electronic with their counterparts will not form colored compounds.

Magnetic Properties

Lanthanum ion(La3+) and Cerium ion (Ce4+) have no 4f electrons while Lutetium (Lu3+)has 14 electrons in the f shell which means there are no unpaired electrons in them.Hence they are diamagnetic. All the other lanthanides will have unpaired electronswhich are responsible for their paramagnetic quality. The paramagnetism increaseswith increase in the number of unpaired electrons.

Oxidation States

Most stable oxidation state among the lanthanides is the +3 state. Certain compoundsin +2 and +4 states are also formed but they are less stable. This is because the sumvalue of the first three ionization energies is lower while the second and fourthionization energies are higher.

Lower oxidation states occur in compounds with bromides and iodides while higher

Characteristics of Lanthanides Back to Top

Uses of Lanthanides Back to Top

oxidation state in fluorides and oxides. The oxidation states +2 and +4 are possibleonly if this leads to either a noble gas configuration, fully filled orbital state or half filledorbital state.

The following table gives the idea of the similarities of the lanthanides in relation to theionization energies, electrode potentials and ionic radii. The gradual reduction in theatomic and ionic radius with increase in atomic number is a special characteristic ofthe lanthanides.

Complex Formation

All the lanthanides form complexes with complexing agents like EDTA. Lutetium formsa stronger complex than Cerium because it's the smallest in the series. Although,oxalates are insoluble, oxalate addition with complexing agent results in the formationof a soluble complex.

Chemical Properties of Lanthanides

1. The +3 lanthanide compounds are much more reactive than Aluminiumcompounds but slightly more reactive than Magnesium compounds (refer to theelectrode potentials). They react slowly with cold water but rapidly with hotwater.

2. Hydroxides are precipitated by ammonia as gelatinous precipitates. They areless basic than Ca(OH)2 but more basic than Al(OH)3.

3. Above 300-400c lanthanides react with hydrogen to form solid hydrides. These

hydrides have a non stoichiometric formula with 2H-ions while the metal is in +3state. Yb forms approximately YbH2.5 hydride.

4. Lanthanides tarnish readily in air, forming oxides. On heating with oxygen alsothey form the oxide M2O3. Ce is an exception and forms CeO2.

5. Anhydrous halides are made by heating metal and halogen or alternatively, byheating oxide with the appropriate ammonium halide.

6. Hydrated lanthanum chloride on heating dissociates into Lanthanum oxychloridewith fumes of water and HCl.

7. On arc melting metal with carbon in inert atmosphere, metal carbide is formedwhich has one electron in the conduction band with formula LnC2 and Ln4(C2)3.These carbides with water produce acetylene and hence are called acetylides.

8. At high temperatures lanthanides react with n.P, As, Sb. Like AlN, thesenitrides also give ammonia on getting wet with water.

9. Lanthanides also form a wide variety of oxo salts with nitrates, sulphatesphosphates.

The most significant characteristic of Lanthanides is the contraction of the atomic sizewith increase in atomic number called lanthanide contraction. While moving alongthe lanthanides series from Ce(58) to Lu71, a regular decrease in the size of theatom/ion and increase in atomic number is observed. This decrease in size is calledthe lanthanide contraction. The decrease in size, though continuous, is not regular.Lanthanide contraction takes place due to imperfect shielding of one 4f- electron whichincreases by one more in the same sub-shell.

The covalent and ionic radii are periodic properties. In the periodic table the radiiincreases in a group from top to bottom since there is an orbit added in a group forevery step downwards. The covalent and ionic radii decrease in a period going fromleft to right because every added electron and proton increases the effective nuclearcharge.

The shielding effect of electrons decreases in the order s>p>d>f. In case of d blocktransition elements, the decrease is not very significant. In case of lanthanides theadditive effect over 14 lanthanides from Ce to Lu is about 0.2 which is quitesignificant. This is called lanthanide contraction which is a characteristic oflanthanides.

The electron filling in a lanthanide is at n-2 level and hence the combining capacity ofthe metal is decided by the n-1 d orbital electrons. The most common valency of 3 forthe lanthanide compounds is another characteristic of Lanthanide. The lanthanides aresoft and silvery white metals. They are very reactive. Heavier metals are less reactivethan the lighter metals.

1. Monazite sand is a source of lighter lanthanides in their trivalent phosphateform. The application of Lanthanide elements as biological tracers is used to

P-block Elements Noble Gas

trace the effectiveness and target route of drugs in humans and animals. Astheir peaks are narrow and very characteristic, they can be easily followed inthe system by spectroscopy.

2. Many lanthanides show fluoresce in Ultra violet radiation, which is used tostudy the defects in metals etc.

3. Lanthanides are strong reducing agents and are also used as catalysts. 4. Lanthanides are used in lamps, lasers and in projector lighting.5. Cigarette lighter flints are made out of a special alloy of lighter lanthanides and

are known as Misch metal. They are also used in X-ray, and focus lights. Dueto its magnetic qualities, the lanthanides are used to make magnets.

6. Thus, Lanthanides find extensive use in various industrial and researchapplications.

More topics in LanthanidesElectron shells

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