D-Block Elements: Transition Metals Explained

D-Block Elements

• D-block elements are located in the middle of the periodic table, specifically Groups 3-12.
• Characterized by the last electron entering the d-orbital.
• Commonly known as transition elements.
• Zinc, cadmium, and mercury are exceptions, not always considered transition elements due to their electronic configurations.

Electronic Configuration

• The general electronic configuration is expressed as (n-1)d^(1-10)ns^(0-2).
• (n-1) signifies the penultimate shell.
• Half-filled and fully filled d-orbitals enhance stability, impacting electronic configurations.

Metallic Properties

• Exhibit typical metallic attributes: high thermal and electrical conductivity, luster, and malleability.
• Transition elements create metallic bonds using unpaired d-electrons.
• Stronger metallic bonding leads to high melting and boiling points.
• Melting points increase with more unpaired d-electrons, then decrease as electron pairing increases.
• Tungsten's exceptionally high melting point is due to its strong metallic bonding.

Atomic and Ionic Sizes

• Atomic size initially decreases across a period because of increasing nuclear charge.
• Atomic size remains relatively constant towards the end of the series because of the shielding effect.
• The first transition series shows decreasing atomic radii up to iron, after which sizes are nearly identical.
• Ionic sizes generally decrease with increasing nuclear charge.
• Lanthanide contraction refers to the gradual reduction in atomic and ionic sizes of lanthanides with increasing atomic number, affecting subsequent elements.
• The 4f orbitals' shielding effect is less effective, increasing effective nuclear charge and reducing size.
• Second and third transition series elements have similar properties due to lanthanide contraction.

Ionization Enthalpies

• Ionization enthalpy is the energy needed to remove an electron from an isolated gaseous atom.
• Transition elements have high ionization enthalpies.
• Variable oxidation states arise from the small energy difference between ns and (n-1)d orbitals.
• Copper's second ionization enthalpy is higher than its first due to the high hydration energy compensating for the energy required to form Cu2+.

Oxidation States

• Transition elements display variable oxidation states.
• Scandium only exhibits a +3 oxidation state.
• Manganese shows the most oxidation states, ranging from +2 to +7.
• Elements achieve their highest oxidation state when combined with highly electronegative elements like oxygen and fluorine.

Standard Electrode Potentials

• Standard electrode potential (E°) measures an element's potential to lose or gain electrons.
• More negative E° values indicate a greater tendency for oxidation (reducing agent behavior).
• More positive E° values indicate a greater tendency for reduction (oxidizing agent behavior).
• Copper has a positive E° value, which means it does not readily oxidize.
• The stability of the hydrated ion and the enthalpy of sublimation also influence E° values.

Trends in Electrode Potentials

• Across a transition series, E° values become less negative.
• Irregularities are observed due to variations in ionization enthalpies and sublimation energies.
• Electrode potential data determines the stability of an oxidation state.

Magnetic Properties

• Magnetic properties depend on the presence of unpaired electrons in an atom or ion.
• Paramagnetic substances are attracted to a magnetic field because of unpaired electrons.
• Diamagnetic substances are repelled by a magnetic field because all electrons are paired.
• The magnitude of paramagnetism is measured in Bohr magnetons (BM).
• The "spin-only" formula, μ = √n(n+2), calculates the magnetic moment (where n is the number of unpaired electrons).
• Higher numbers of unpaired electrons result in higher magnetic moments.

Formation of Colored Ions

• The color of transition metal ions arises from d-d transitions.
• When white light passes through a solution of transition metal ions, some wavelengths are absorbed.
• Observed color corresponds to the complementary color of absorbed wavelengths.
• Unpaired d-electrons are vital for d-d transitions.

Complex Formation

• Transition metals readily form complexes because of their small size, high charge, and available d-orbitals.
• Ligands are ions or molecules that donate electron pairs to form coordination complexes.

Catalytic Properties

• Transition metals and their compounds serve as catalysts due to their ability to exhibit multiple oxidation states.
• They can form unstable intermediates, lowering the energy pathway for reactions.
• Transition metals provide a surface for reactant molecules to bind and react.

Interstitial Compounds

• Interstitial compounds form when small atoms (H, C, N) are trapped within the crystal lattice of metals.
• These compounds are non-stoichiometric, hard, and have high melting points.

Alloy Formation

• Alloys are solid solutions made of two or more metals.
• Transition metals form alloys because of similar atomic sizes and properties.

Potassium Dichromate (K2Cr2O7)

• Prepared commercially from chromite ore (FeCr2O4).
• Conversion involves reacting chromite ore with sodium carbonate to form sodium chromate.
• Sodium chromate converts to sodium dichromate through acidification.
• Potassium dichromate is obtained by adding KCl to sodium dichromate because it is less soluble.
• Potassium dichromate forms orange crystals.
• In aqueous solution, chromate and dichromate ions are in pH-dependent equilibrium.
• Dichromate ion is an oxidizing agent, especially in acidic conditions.

Oxidizing Action of Dichromate

• Oxidizes ferrous ions to ferric ions.
• Oxidizes iodides to iodine.
• During redox reactions, dichromate ions reduce to Cr3+ ions, turning the solution green.

Potassium Permanganate (KMnO4)

• Prepared from pyrolusite ore (MnO2).
• Fusion of MnO2 with KOH in air or KNO3 produces potassium manganate (K2MnO4).
• Manganate ion converts to permanganate ion through electrolytic or oxidative chlorination.
• Potassium permanganate forms purple crystals.
• In aqueous solution, permanganate ion is a strong oxidizing agent.

Oxidizing Action of Permanganate

• In acidic medium, it produces Mn2+ ions.
• Functions as a self-indicator in titrations.
• Oxidizes ferrous salts to ferric salts.
• Oxidizes oxalic acid to carbon dioxide.
• Oxidizes iodides to iodine.

The f-Block Elements

• The f-block elements include lanthanoids and actinoids.
• Characterized by the last electron entering the f-orbital.
• Also referred to as inner transition elements.

Lanthanoids

• Consist of 14 elements following lanthanum (La).
• Their electronic configuration is [Xe] 4f^(1-14) 5d^(0-1) 6s^2.
• Primarily exhibit a +3 oxidation state.
• Lanthanide contraction is the gradual decrease in ionic size with increasing atomic number.
• Separation is challenging because of similar chemical properties.

Actinoids

• Comprise the 14 elements following actinium (Ac).
• Their electronic configuration is [Rn] 5f^(1-14) 6d^(0-1) 7s^2.
• Exhibit variable oxidation states.
• These elements are radioactive and synthetic.

Explore the d-block elements, located in Groups 3-12 of the periodic table, focusing on their electronic configuration and metallic properties. Learn about their role as transition metals and the exceptions like zinc. Understand how unpaired d-electrons contribute to metallic bonding, influencing melting and boiling points.