F Block Elements on the Periodic Table


F-Block Elements on the Periodic Table

The f-block elements or the inner transition metals are a set of elements found in the periodic table. They are the elements in the two rows at the bottom of the periodic table, separated from the main body of the table. The defining feature of these elements is the filling of their f-orbitals, which differentiates them from the d-block (transition metals) and s-block and p-block elements (main group elements). The “f” stands for “fundamental” or the azimuthal quantum number 3.

General Electron Configuration

The general electron configuration for f-block elements is: (𝑛−2)𝑓1−14(𝑛−1)𝑑0−1𝑛𝑠2 where 𝑛 is the principal quantum number of the outermost shell. For example, the noble gas electron configuration of cerium is [Xe] 4f1 5d1 6s2, while the electron configuration of curium is [Rn] 5f7 6d1 7s2.

Location on the Periodic Table

The f-block elements fall into two series:

  1. Lanthanides (Lanthanoids): Elements with atomic numbers 57 (Lanthanum) through 71 (Lutetium).
  2. Actinides (Actinoids): Elements with atomic numbers 89 (Actinium) through 103 (Lawrencium).

In a traditional periodic table these elements are at the bottom of the periodic table to keep the table more compact and to emphasize their unique properties. However, in the extended periodic table, the f-block elements are between groups 2 and 3.

Extended Periodic Table

Why Are F Block Elements Called Inner Transition Metals?

The other name for the f-block elements is the inner transition metals. They inner transition metals due to their position within the periodic table and their unique electron configurations, which involve the filling of inner f-orbitals.

  • Between Transition Metals: They are between the s-block and d-block elements. This positioning reflects their transitional nature between the main groups and the d-block transition metals.
  • Electron Configuration: The defining feature of the f-block elements is the progressive filling of the 4f and 5f orbitals. This inner layer of electron configuration is what differentiates them from the d-block transition metals, where the d-orbitals are being filled.
  • Inner Transition: The term “inner transition” highlights that the electrons being added are within the (n-2)f orbitals, which are two principal quantum levels below the outermost shell. For example:
    • In the lanthanides, the electrons fill the 4f orbitals (with n=6 for the outermost shell).
    • In the actinides, the electrons fill the 5f orbitals (with n=7 for the outermost shell).
  • Contrast with d-Block Transition Metals: The d-block elements, or transition metals, involve the filling of d-orbitals in their electron configurations. These d-orbitals are only one principal quantum level below the outermost shell (e.g., 3d, 4d, 5d).

Classification and Nomenclature

Lanthanides: This series includes the 15 elements from Lanthanum (La) to Lutetium (Lu). They take their name for the first element in the series, Lanthanum.

Actinides: This series includes the 15 elements from Actinium (Ac) to Lawrencium (Lr). Their names comes from the first element in the series, Actinium.

While the terms “lanthanides” and “actinides” are common, some prefer the terms “lanthanoids” and “actinoids” to indicate their nature as a series rather than implying they are derived from Lanthanum or Actinium.

Elements in Each Group

Here is a complete list of the f-block elements, according to whether they are lanthanides or actinides:

Lanthanides:

  • Lanthanum (La)
  • Cerium (Ce)
  • Praseodymium (Pr)
  • Neodymium (Nd)
  • Promethium (Pm)
  • Samarium (Sm)
  • Europium (Eu)
  • Gadolinium (Gd)
  • Terbium (Tb)
  • Dysprosium (Dy)
  • Holmium (Ho)
  • Erbium (Er)
  • Thulium (Tm)
  • Ytterbium (Yb)
  • Lutetium (Lu)

Actinides:

  • Actinium (Ac)
  • Thorium (Th)
  • Protactinium (Pa)
  • Uranium (U)
  • Neptunium (Np)
  • Plutonium (Pu)
  • Americium (Am)
  • Curium (Cm)
  • Berkelium (Bk)
  • Californium (Cf)
  • Einsteinium (Es)
  • Fermium (Fm)
  • Mendelevium (Md)
  • Nobelium (No)
  • Lawrencium (Lr)

Properties of f-Block Elements

The f-block elements share certain common properties, regardless of whether they are lanthanides or actinides.

  • They are metals and have properties similar to the d-block elements or transition metals.
  • The +3 oxidation states is the most common, but other oxidation states also occur.
  • The f-block elements are electropositive and reactive.
  • These elements have magnetic properties.
  • Increasing atomic number correlates with decreasing atomic and ionic radius.

However, these two series of elements have distinctive properties, too.

Lanthanides:

  • Chemical Reactivity: Lanthanides are highly reactive, especially at high temperatures. They readily react with oxygen to form oxides and with water to form hydroxides.
  • Magnetic Properties: Several lanthanides exhibit strong magnetic properties. For example, gadolinium has high magnetic susceptibility.
  • Color and Spectra: Lanthanides display a range of colors due to the electronic transitions within the 4f orbitals. This makes them useful in various optical applications.
  • Oxidation States: The common oxidation state for lanthanides is +3, though +2 and +4 states are also common.

Actinides:

  • Radioactivity: All actinides are radioactive. This radioactivity increases with higher atomic numbers, with elements like Uranium and Plutonium being well-known for their use in nuclear energy.
  • Complex Chemistry: Actinides exhibit a wide range of oxidation states, typically from +3 to +6, which results in complex chemistry.
  • Density and Melting Points: Actinides have high densities and high melting points, making them suitable for high-temperature applications.

Uses of f-Block Elements

Lanthanides:

  • Magnets: Neodymium magnets are among the strongest permanent magnets, widely used in electronics, motors, and wind turbines.
  • Optics: Lanthanides are important in the production of phosphors for color television tubes, LED lights, and lasers.
  • Catalysts: They are catalysts in industrial chemical reactions and in catalytic converters in automobiles to reduce emissions.

Actinides:

  • Nuclear Energy: Uranium and Plutonium are critical fuels for nuclear reactors and in nuclear weapons.
  • Medicine: Certain actinides, like Californium-252, are useful in cancer treatment for radiotherapy.
  • Research: Actinides are key in scientific research that studies nuclear reactions and properties of elements.

References

  • Jensen, William B. (2015). “The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table: an update”. Foundations of Chemistry. 17: 23–31. doi:10.1007/s10698-015-9216-1
  • Petrucci, Ralph H.; Harwood, William S.; Herring, F. Geoffrey (2002). General Chemistry: Principles and Modern Applications (8th ed.). Upper Saddle River, N.J: Prentice Hall. ISBN 978-0-13-014329-7.
  • Scerri, Eric (2021). “Provisional Report on Discussions on Group 3 of the Periodic Table”. Chemistry International. 43 (1): 31–34. doi:10.1515/ci-2021-0115
  • Thyssen, P.; Binnemans, K. (2011). “Accommodation of the Rare Earths in the Periodic Table: A Historical Analysis”. In Gschneidner, K. A. Jr.; Bünzli, J-C.G; Vecharsky, Bünzli (eds.). Handbook on the Physics and Chemistry of Rare Earths. Vol. 41. Amsterdam: Elsevier. pp. 1–94. doi:10.1016/B978-0-444-53590-0.00001-7