The D and F Block Elements

The d-block of the periodic table includes elements from groups 3 to 12. These elements fill up the d orbitals across the four long rows in the table. On the other hand, the f-block contains elements where the 4f and 5f orbitals are filled up. These elements are placed separately at the bottom of the table. We commonly call the elements in the d-block "transition metals" and the ones in the f-block "inner transition metals."

1.0The Transition Elements (d-Block)

The d-block occupies the central portion of the periodic table, situated between the s-block and p-block elements. Within this section, the d-orbitals of the penultimate energy level of atoms accept electrons, leading to the emergence of four rows of transition metals: the 3d, 4d, 5d, and 6d series.

2.0Electronic Configuration

• The electronic configuration of d-block elements typically follows the pattern(n – 1)d^1-10ns^{0 –2}. 
• However  elements such as  Zn, Cd, Hg, etc., which have completely filled d-orbitals [(n – 1)d¹⁰], are considered d-block elements but not transition metals.

3.0Properties of d Block

Transition elements, also known as transition metals, exhibit several general properties:

• Variable Oxidation States: Transition metals can exist in multiple oxidation states due to the availability of d-electrons that can be easily lost or gained in chemical reactions.
• Formation of Colored Compounds: Many transition metal compounds display vivid colors due to d-electrons transition, which can emit specific wavelengths of light.
• Formation of Complex Ions: Transition metals readily form complex ions by coordinating with ligands, molecules, or ions that donate electron pairs to the metal ion.
• Catalytic Activity: Transition metals often act as catalysts in various chemical reactions due to their ability to change oxidation state during the reaction process.
• Paramagnetism: Transition metal ions with unpaired electrons are often paramagnetic, attracting them to an external magnetic field.
• High Melting and Boiling Points: Transition metals typically have high melting and boiling points due to strong metallic bonding resulting from d-electrons.
• Malleability and Ductility: Transition metals are generally malleable and ductile, hammered into thin sheets or drawn into wires without breaking.
• Density: Transition metals tend to have high densities compared to other elements.
• Formation of Alloys: Transition metals readily form alloys with other metals, resulting in materials with enhanced properties such as strength and corrosion resistance.

4.0Importance in Catalysis

Transition metals are essential catalysts in various chemical reactions due to their ability to transition between different oxidation states. In given examples, transition metals accelerate reactions by providing active surfaces for reactants, enhancing reaction rates and efficiency.

• Haber’s Process: Iron catalyzes ammonia synthesis by providing a surface for nitrogen and hydrogen molecules to react and produce ammonia efficiently.
• Hydrogenation of Alkenes: Nickel catalyzes the hydrogenation of alkenes into alkanes by adsorbing both the alkene and hydrogen molecules, facilitating their addition reaction.
• Contact Process: Vanadium(V) oxide acts as a catalyst in sulfuric acid production, speeding up the oxidation of sulfur dioxide to sulfur trioxide by atmospheric oxygen.

5.0Compounds of Transition Elements

Important Compounds of Transition Elements are listed below:

• Potassium Dichromate (K₂Cr₂O₇) is used in the leather industry and as an oxidizing agent in azo compound preparation due to its potent oxidizing capabilities.
• Potassium Permanganate (KMnO₄) is a strong oxidant employed in organic chemistry, textile bleaching, and oil decolorization. It is characterized by its striking purple color and varying magnetic properties with temperature.
• Ferrous Sulfate (FeSO₄): Widely used in medicine and agriculture, it is an iron supplement for treating anemia and a soil amendment for enhancing crop yields by correcting iron deficiencies in plants.
• Cobalt Chloride (CoCl₂): Noted for its blue color, cobalt chloride functions as a humidity indicator in desiccants. It undergoes reversible hydration reactions to change color in response to varying humidity levels.

6.0The Inner Transition Elements (f-block)

The f-block elements comprise two series of elements: the Lanthanides, also known as Lanthanons, and the Actinides, also known as Actanones. These elements encompass 28 elements from atomic number 58 to 71 and from atomic number 90 to 103, arranged in two horizontal rows below the main body of the Periodic Table.

The f-block elements are those in which the f orbitals are being filled with electrons. These elements typically have electrons filling the f orbitals, ranging from 1 to 14, alongside 0 to 1 electron in the d orbital of the penultimate energy level and the outermost orbital.

• f-block elements are categorized into two series: lanthanides and actinides. This block of elements is commonly referred to as inner transition metals due to its role in bridging the gap between the s block and d block elements in the periodic table, providing a transition within the 6th and 7th rows.
• These two series within the f-block correspond to the filling of the 4f and 5f orbitals. The 4f series spans from Ce to Lu and encompasses 14 elements, while the 5f series ranges from Th to Lw and also comprises 14 elements. These elements are characterized by the gradual filling of the f orbitals within each series.

Properties of Lanthanides

• Soft, silvery-white metals.
• Tend to dull and lose brightness when exposed to air.
• Melting points range from 1000 K to 1200 K (except Samarium, 1623K).
• Good conductors of heat and electricity.
• Mostly non-radioactive, except promethium.
• Exhibit lanthanoid contraction, with decreasing atomic and ionic radii from lanthanum to lutetium.

Properties of Actinides

• Silvery appearance.
• Radioactive nature.
• Highly reactive, mainly when finely divided.
• Exhibit actinoid contraction, with decreasing atomic and ionic radii from Actinium to Lawrencium.
• Predominantly exhibit an oxidation state of +3, although higher oxidation states are common in the first half of the series.

7.0Exceptions in d-block and f-block Elements

• Chromium (Cr) and Copper (Cu): Anomalies in electron configuration where Cr is [Ar] 3d⁵ 4s¹ and Cu is [Ar] 3d¹⁰ 4s¹, due to stability gained by half-filled (Cr) and fully-filled (Cu) d orbitals.
• Lanthanum (La) and Actinium (Ac): Their electron configurations deviate from expected patterns due to small energy differences between 5d and 4f orbitals, resulting in [Xe] 5d¹ 6s² for La and [Rn] 6d¹ 7s² for Ac.
• Lanthanide Contraction: Refers to the unexpected decrease in atomic and ionic radii in the lanthanide series due to poor shielding of 4f electrons, causing increased nuclear attraction on outer electrons.

These exceptions highlight the intricacies of electron behavior in transition metals and inner transition metals, deviating from the expected Aufbau principle.

8.0Comparison of d and f block Elements