Lanthanides – Electronic configuration, Oxidation state, and Uses

Lanthanides are those elements in which the last electron enters into anti-penultimate 4f sub-shell. These are the elements from Ce₅₈ to Lu₇₁ that lie in the 6^th period of the periodic table and are called f-block elements since the differentiating electron (last electron) in the atom of these elements enters the f sub-shell belonging to anti-penultimate shell [(n-2)^th shell].

Electronic Configuration of Lanthanides

The general electronic configuration of the Lanthanide element is

[Xe] 4f^1-14 5d^10-1 6s²

Since the inner electron level, 4f orbitals are successively filled from (4f¹ to 4f¹⁴) though there are outer incompletely filled electron levels, these elements are called inner transition elements and the series are called inner transition series.

The electronic configuration of lanthanide elements are

Although La lacks f electrons, its properties are comparable to those of the lanthanides, therefore it is classified and studied alongside them.

The 14 elements from Cerium to Lutetium are expected to be formed by adding 1,2,3…….14 electrons to the 4f-level. In most electrons, however, moving single 5d electrons into the 4f level is energetically advantageous, but not in Ce, Gd, or Lu. Gd has a 5d¹ configuration because it provides a half-filled 4f level, which provides extra stability. Because the f shell is already occupied, Lu has a 5d¹ configuration. The lanthanides are distinguished by the fact that all of the metals have the same +III oxidation state.

Oxidation States of Lanthanides

All lanthanides exhibit the most common and stable oxidation state of +3. This is because the sum of each lanthanide’s first three ionization energies is low, allowing them to easily form their trivalent states. Other oxidation states +2 and +4 do exist for some lanthanides, however, they are less stable than +3. Hence oxidation state +2 and +4 occurs when they lead to

• noble gas configuartion e.g. Ce⁺⁴ (f⁰)
• a half-filled f-shell e.g. Eu²⁺ and Tb⁴⁺ (f⁷)
• a completely filled f-shell e.g. Yb²⁺ (f¹⁴)

Furthermore, elements that are near to these states also possess (+II) and (+IV) states. Examples: Sm²⁺ and Tm²⁺ have f⁶ and f¹³ arrangements, respectively, while Pr⁴⁺ and Nd⁴⁺ have f¹ and f² configurations.

Magnetic properties of Lanthanides

Since the elements like La³⁺ and Ce⁴⁺ have noble gas configuration (f⁰), and Lu³⁺ has a completely filled f-shell configuration (f¹⁴), these elements are diamagnetic due to the absence of unpaired electrons. All other f states are paramagnetic as they have unpaired electrons.

The magnetic moment of the transition elements can be calculated by using the formula:

where, µ_(S+L)= magnetic moments in Bohr magnetons, S = resultant spin quantum number, and L= resultant orbital momentum quantum number.

Solubility of Lanthanides

Many salts follow the pattern of group 2 elements in terms of solubility. Thus, chlorides and nitrates are soluble in water, whereas oxalates, carbonates, and fluorides are not; however, suplhates are. Many lanthanides combine with group 1 or ammonium salts to form double salts. Because these double salts crystallize well, they’ve been utilized to separate the lanthanides.

Color and Spectra of Lanthanides

The lanthanides ions absorb light in the near-ultraviolet and visible ranges. The color of these elements is due to the presence of unpaired f-electrons which take part in the f-f transition. All the Ln³⁺ except Lu³⁺ are coloured, both in their salts and aqueous solutions. Crystal field splitting has a significant role in the spectra of transition metals.

Uses of Lanthanides

• Used as catalysts in the production of petroleum and synthetic products.
• Used for making steel alloys.
• Lanthanide oxides are used to color ceramics and glasses and are also used as phosphors on television screens.
• Cerium oxide (CeO₂) is used to polish glass.
• Samarium is used in laser lamps.
• Lanthanide-cobalt alloys are used for making permanent magnets.
• Used for the removal of Sulphur and oxygen impurities.

Lanthanides Video

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References

• J. D. Lee, Concise Inorganic Chemistry, 5th Edition, John Wiley and Sons. Inc. 2007.
• F. A. Cotton, G. Wilkinson & C. Gaus, Basic Inorganic Chemistry, 3 rd Edition, John Wiley & Sons (Asia), Pvt., Ltd., 2007.
• D. F. Shriver & P. W. Atkins, Inorganic Chemistry, 5th Edition, Oxford University Press, 2010.