Lanthanides are rare earth elements. They are also known as inner transition elements. The symbol Ln is used for the discussion of any lanthanide. However, these elements include the atomic numbers 57-71 from lanthanum to lutetium. These elements are known as lanthanides due to their similarity with lanthanum. The lanthanides are f-block elements due to the filling of the 4f electron shell. However, lanthanum is a d-block element. They can be prepared by different methods like ion exchange, complex formation, fractional crystallization, etc.
Electronic configuration of lanthanide
The general electronic configuration of the lanthanide is the following:
[Xe]4f1-145d0-16s2
The energy difference between the 4f and 5d orbital is very small. So, electrons enter into the 4f orbital and the 5d orbital remains vacant.
Exceptions are in the case of gadolinium (Gd) and lutetium (Lu). This is because of the presence of more stable half-filled or full-filled f orbital.
Oxidation states of lanthanide
The lanthanides exhibit variable oxidation states. These states range from +2 to + 7. All the lanthanides show an oxidation state of +3. The lanthanides exhibit the +2 oxidation state in their complexes in solution. However, the +4 oxidation state of the cerium is favored. This is because it attains noble gas electron configuration.
Lanthanide contraction
The lanthanides contraction is the steady decrease in the size of the along the series from lanthanum to lutetium. This is because of the poor shielding of one 4f electron to another. As the nuclear charge increases from La-Lu. Therefore, a regular decrease in the size of La-Lu.
Preparation of lanthanide
Lanthanides are extracted from different ores. For example, monazite is treated with hot concentrated sulphuric acid. Thorium, lanthanum, and other lanthanoids are dissolved as sulfates. Hence they separated from insoluble material. The various lanthanide elements are separated by different methods. Some are given below:
Reduction of trihalide
La, Ce, Pr, Nd, and Gd can be obtained by the reduction of their trichlorides. This can be done with calcium at about 1000 centigrade in argon filled vessel. The heavier lanthanoids such as Tb, Dy, Ho, Er, and Tm can also be obtained by this method. However, for these lanthanides, we use trifluoride instead of trichloride. This is because trichloride is volatile and heavier lanthanides have high boiling points. So, they require a temperature of 1400 centigrade. Hence, at this temperature chlorides boils.
Ion exchange method
The ion exchange method of separation of the lanthanides is based on the solubility of a complex ion. All lanthanides form +3 ions whose ionic radii decrease progressively with increasing atomic numbers. However, from Ce+3 to Lu+3 the solution containing +3 lanthanides is placed at the top of the column of cation ion exchange resin such as Dowex 50. The Ln+3 ions are absorbed into the resin. Hence, an equivalent amount of the H+ions are released from the column.
Ln+3 + 3H+K– → Ln+3(R–) + 3H+
The Dowex 50 is an ion exchange resin containing a carboxylic acid group. A citrate buffer is slowly run down in the column. Hence, the cations partition themselves between the column and the moving citrate solution. Since the smaller ion shows a greater affinity for complexing with citrate solution. Therefore, these ions are the first to emerge from the column. So, Lu+3 emerges first from the column due to its smaller size.
Valency change method
The different properties of various oxidation states make separation easy. For example, the properties of Ln+4 and Ln+3 are very different from each other Ce can be separated from other lanthanides. This is because it is the only one which has a +4 oxidation state ion in an aqueous solution that is stable.
A solution containing a mixture of Ce+3 can be oxidized with NaOCl under alkaline conditions. However, it produces Ce+4 which is much smaller than Ce+3. So, they can separate by controlling precipitation.
Physical properties of Lanthanide
The physical properties of the lanthanides are the following:
- Almost all the lanthanides are silvery white in color.
- They have high melting and boiling points.
- They are good conductors of electricity.
- They are involved in the formation of colored ions.
- Some of the lanthanides are paramagnetic and others are diamagnetic.
Chemical properties of lanthanide
The chemical properties of the lanthanides are given below:
- They readily tarnish in the air and burnt to give oxides. All give trioxide except Ce which gives dioxide.
- They also combine with non-metals like N, S, and X.
- Lanthanides can liberate hydrogen from water.
2Ln + 6H2O → 2Ln(OH)3 + 3H2
- Lanthanide compounds are ionic.
Coordination complexes of lanthanide
The Ln+3 ion readily forms complexes with oxygen and floor donor ligands. Such as water, EDTA, etc. However, partially fluorinated ligand produces complexes with Ln+3 that are volatile. They are used as precursors for the synthesis of the lanthanide-containing superconductor by vapor deposition.
Concepts Berg
What is special about lanthanide?
Lanthanides are distinctive in terms of their magnetic and electronic properties. Some lanthanides have important applications.
Are lanthanides a metal or nonmetal?
All lanthanides are metals. However, they are very hard and have high melting and boiling points.
What is the first lanthanoid element?
Lanthanum is the first element of the lanthanides series.
What are the uses of lanthanide?
Some lanthanides are used as a catalyst. They are used in batteries such as salts of cerium.
Where are lanthanides found?
Lanthanides are rare earth metals. They are naturally occurring metals. Most of the lanthanides are present in the monazite (dark sand).
Why are lanthanides called lanthanides?
Lanthanides are named by showing similarities to lanthanum. So, “lanthanides” means like lanthanum.
Do lanthanides rust or corrode?
The lanthanides are corroded easily when they expose to the air.
What is the reason behind the coloration of lanthanide ions
The lanthanides show color due to the f-f transition. However, this transition is due to the presence of unpaired electrons.
Reference Books
- Inorganic chemistry by Catherine E. Housecroft and Alan G. Sharpe
Reference Links
- Lanthanide (Wikipedia.org)
