f-Block Chemical Elements Lanthanum and Actinium
f block elements appear in two chemical series like 4f blocks and 5f blocks names as lanthanides or rare earth and actinides or actinoids in the periodic table. Lanthanides in f-block chemical elements constitute the first inner transition series while actinides constitute the second inner transition series in chemistry. The electronic configuration of the f-block chemical elements or lanthanum and actinium has been done by filling electrons in deep-seated 4f and 5f orbital with the increasing atomic number. The trivalent oxidation state of all f-block chemical elements or lanthanides and actinides is a stable or common oxidation state.
The 4f block contains fourteen chemical elements cerium to lutetium with an atomic number from 58 to 71. These f-block chemical elements are known as Lanthanum because they appear after lanthanum. Also, the 5f block contains fourteen chemical elements thorium to lawrencium with atomic numbers 90 to 103. These f-block chemical elements are known as actinides because they appear after actinium.
Chemical Properties of f-block Elements
The f-block chemical elements like lanthanides behave as active metals. Therefore, the redox reaction potential of these chemical elements comparable to alkaline earth metals. All the f-block metals act as strong reducing agents and chemical reactions with acids by the liberation of hydrogen ions. Hence they absorb hydrogen ions from low pH solutions to form interstitial hydrides.
Although important similarities exist between the two series of the f-block elements but very impotent differences also occur. These differences occur due to lower bond energies, ionization energy, and less effective shielding electron in 5f block elements than the 4f-block elements. The standard electrode potentials for f-block lanthanides become more positive with the increasing atomic number. But for actinium, electrode potentials values become more positive from actinium to uranium and become less positive till Americium.
f Block Lanthanides in Periodic Table
The 4f block chemical elements in the periodic table have been variously called rare earth, lanthanum’s, and lanthanum. The name rare-earth for f-block has been 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 chemical elements are no longer rare but are abundant. The general valence shell electronic configuration of lanthanum atoms [Pd] 4fn 5s2 5p6 5d1 6s2. Therefore, the valence shell electronic configuration of trivalent ion is [Pd] 4fn 5s2 5p6 5d1 6s2, where n has values 1 to 14.
4f-block is 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 orbital contains 6s-electrons and the inner energy orbital contains f-electrons.
Cerium Gadolinium Lutetium in Periodic Table
f-block chemical elements like Cerium, Gadolinium, and Lutetium in the periodic table contain one electron in 5d orbital with atomic numbers 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.
The f-electrons of similar spin, repulsion is less by an amount called the exchange energy of an electron. But the greater the number of f-electrons with parallel spins the greater of exchanged interaction and greater stability. This is the basis of Hound’s rules and uses to derive the electronic arrangement of Cerium, Gadolinium, and Lutetium.
Electron Configuration of Cerium
The electron configuration of cerium, [Pd] 4f1 5S2 5P6 5d1 6S2. Therefore, the cerium atom contains one electron in a 5d orbital. But 4f and 5d energy levels are very close in terms of energy. Therefore, the half-filled orbital f-block chemical elements like cerium slightly more stable than orbital with one additional electron.
Electron Configuration of Gadolinium
The electron configuration of f-block chemical elements like 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. Here the half-filled energy level stabilizes by exchange energy in the 4f orbital of the gadolinium atom.
Electron Configuration of Lutetium
Lutetium also has a valence orbital electronic configuration, f14 d1, where the last electrons have added the capacity of the f-shell. Therefore, the electronic configuration f-block chemical chemical elements like Lutetium, [Pd] 4f14 5s2 5p6 5d1 6s2.
Praseodymium Electronic Configuration
Praseodymium in f-block 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 are 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 chemical elements like lanthanum. Because the removal of three electrons from lanthanides is easier than the removal of greater than three electrons. Therefore the ground state electronic configuration of lanthanum’s atoms and trivalent lanthanum’s ions are [Pd] 4fn 5s2 5p6 5d1 6s2 and [Pd] 4fn 5s2 5p6 respectively, 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.
5f Block Chemical Elements Names-Actinides
The second series of 5f block chemical elements results from the filling of 5f-orbital. Actinides in f block consist of chemical elements like thorium to lawrencium with atomic numbers 90 to 103.
5f-block actinides atoms and actinides (M+3), [Rn] 4fn 5d1-2 6s2, and [Rn] 4fn respectively, 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 the emission of alpha, beta or gamma rays. 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 f-block actinides ion and crystalline solid chemical elements contain narrow bands with visible, near-ultraviolet, and near-infrared spectrum in electromagnetic spectrum radiation.