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f block Elements

f-Block Elements Lanthanum and Actinium

f block elements appear in two series like 4f blocks and 5f blocks names as lanthanides or rare earth and actinides or actinoids in the periodic table. Lanthanides constitute the first inner transition series while actinides constitute the second inner transition series in chemical science. The electronic configuration of lanthanum and actinium has done filling electron in deep-seated 4f and 5f orbital with the increasing atomic number of the chemical element. The trivalent oxidation state of lanthanides and actinides is a stable oxidation state. The 4f block contains fourteen elements cerium to lutetium with the atomic number from 58 to 71. These are Lanthanum’s as they appear after lanthanum. Also, the 5f block contains fourteen chemical elements thorium to lawrencium with atomic number 90 to 103. These elements are called actinides because they appear after actinium.

Atomic number electron configuration of f block elements Lanthanides in periodic table

Chemical Properties of f-block Elements

The lanthanides behave as active metals and redox potential of these elements comparable to alkaline earth. Therefore, all the metals act as strong reducing agents and chemical reactions with acids by the liberation of hydrogen ion. They absorb hydrogen to form interstitial hydrides.

Although important similarities exist between two series of f-block elements but very impotent differences also occur. These differences are due to lower bond energies and less effective shielding in 5-f block electrons than those of 4f-electrons. The standard electrode potentials for lanthanides become more positive with the increasing atomic number while for actinium these values become more positive from Ac to U and become less positive till Am.

f Block Lanthanides in Periodic Table

The 4f block in the periodic table has been variously called rare earth, lanthanum’s, and lanthanum. The name rare earth has given because they originally extracted from oxides for which ancient name earth and which are considered to be rare in earth environment. The term rare-earths now avoided because many of these elements are no longer rare but are abundant. The general valence shell electronic configuration of lanthanum atoms and their trivalent ion is,

Lanthanum atoms
[Pd] 4fn 5S2 5P6 5d1 6S2
where n has values 1 to 14
Lanthanum (M+3) ions
[Pd] 4fn 5S2 5P6
where n has values 1 to 14

4f-block also called inner transition elements. Because the electron particles are added to the deep-seated 4f-orbital with the increasing atomic number of lanthanum. Therefore, the outer electronic configuration of 4f block elements 6s2 and inner energy orbital contains f -electrons.

Cerium Gadolinium Lutetium in Periodic Table

Cerium, Gadolinium, and Lutetium in the periodic table contain one electron in 5d orbital with atomic number 58, 64, and 87. Therefore the electron configuration of cerium, gadolinium, and lutetium outside of the general electronic configuration. Because electrons of similar spin developed an exchange interaction which leads to stabilizing the system.

Hence the electrons of similar spin, repulsion is less by an amount called the exchange energy of electron. But the greater the number of electrons with parallel spins the greater of exchanged interaction and greater stability. It is the basis of Hound’s rules of maximum spin municipality.

Electron Configuration of Cerium

The electron configuration of cerium
[Pd] 4f1 5S2 5P6 5d1 6S2

Cerium atom contains one electron in a 5d orbital. But 4f and 5d are very close in terms of energy. Thus the half-filled orbital of cerium slightly more stable than orbital with one additional electron by increasing exchange energy.

Electron Configuration of Gadolinium

The electron configuration gadolinium
[Pd] 4f7 5S2 5P6 5d1 6S2

Gadolinium contains seven electrons with a parallel spin in the seven f-orbitals with the maximum stability of the f orbital. This half-filled energy level stabilizes by exchange energy in 4f orbital of gadolinium atom.

Electron Configuration of Lutetium

Lutetium also has the f14d1 electron configuration where the last electrons have added the capacity of the f-shell.

The electronic configuration Lutetium
[Pd] 4f14 5S2 5P6 5d1 6S2

Praseodymium Electronic Configuration

Praseodymium possesses electronic configuration 4f3 6s2 instead of the expected one 4f2 5d1 6s2. This can be explained by (n + l) rules, the orbital which has a higher value of (n + l) is the higher energy orbitals. For 4f orbital, (n + l) = 4+3 = 7 but for 5d orbital, (n + l) = 5+7 =7.

For 4f and 5d-orbital, the sum of principal and azimuthal quantum numbers are the same. In this case, the highest number of principal quantum numbers is the higher energy quantum systems of an atom. Therefore, 5d-orbital is a higher energy quantum shell. Again electrons fed into orbitals in order of increasing energy until all the electrons have been accommodated. Hence the electron filling process for f block element praseodymium f-electron filling first and possess electronic configuration 4f3 6s2.

Oxidation State of Lanthanides

The trivalent oxidation state is the common oxidation state of lanthanum. Because of the removal of three electrons from lanthanides is easier than the removal of greater than three electrons. The ground state electronic configuration of lanthanum’s atoms and trivalent lanthanum’s ions

Lanthanum’s element
[Pd] 4fn 5S2 5P6 5d1 6S2
Lanthanum ions
[Pd] 4fn 5S2 5P6
where n is 0 to 14 from Lanthanum to Lutetium.

The stability electrons in the f orbital of lanthanides greater than the d and s electrons. Therefore the f electrons can not participate in the chemical bonding and the +3 oxidation number or state is common for lanthanides.

f Block Chemical Elements Names-Actinides

The second series of 5f block elements results from the filling of 5f-orbital. Actinides consist of element thorium to lawrencium with atomic number 90 to 103.

Name and symbol f block elements in periodic table element

Actinides atoms
[Rn] 4fn 5d1-2 6S2
where n has values 1 to 14
Actinides (M+3) ions
[Rn] 4fn
where n has values 1 to 14

The highest atomic number of naturally occurring actinides (f-block elements) = 92. For this reason, uranium occupies the last position in the periodic table for a very long time. Since 1940 seven chemical elements from neptunium to lawrencium have been identified and synthesized by the transformation of naturally occurring elements by nuclear reaction. These men made eleven isotopes that are placed beyond uranium in the periodic table and are collectively called trans-uranium chemical elements. The absorption spectra of actinides ion and in crystals contain narrow bands in the visible, near-ultraviolet, and near-infrared spectrum of the electromagnetic radiation.