d-Block Elements

The d-block elements are part of the periodic table and are also known as transition metals. They span groups 3 to 12 and are characterized by the filling of inner d orbitals as electrons are added across the period. 

What are d-Block Elements?                 

The d block elements in the periodic table are a special group of metals found in the middle part of the periodic table. They have electrons arranged in a certain way called the d-orbitals, giving them some unique qualities. These metals can change how many electrons they have, which helps them do different kinds of chemistry. They make colorful compounds because they can grab and release light.

The d-block, residing at the heart of the periodic table, unfolds into four distinct series aligned with the filling of the 3d, 4d, 5d, or 6d orbitals. Each series reveals how electrons organize within orbitals, providing vital information about how transition metals behave and their distinct properties.

• 3d- Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn
• 4d- Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd
• 5d- La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg
• 6d- incomplete.

What defines these elements is their electron configuration. As electrons populate the d orbitals within these elements, they exhibit a diverse range of features, making them indispensable in various facets of our lives. Let’s discuss several common Chemical and physical properties of d block elements, such as:

1.0Electronic Configuration of d Block Elements

d Block elements names and electronic configuration of d block elements

(A)   General Electronic Configurations-  (n – 1)d^1–10 ns^1–2

The (n–1) stands for the inner d orbitals which may have one to ten electrons.

The (n) stands for the outermost s orbital which may have one or two electrons.

3d Series: The Start of Transition Metals

This series introduces the first set of transition metals found in the fourth row of the periodic table. Metals like scandium (Sc), titanium (Ti), and zinc (Zn) belong to this group, showcasing their unique ways of arranging electrons.

4d Series: Moving Beyond the Fourth Row

Progressing further, the 4d series extends our exploration into transition metals beyond the fourth row. Elements like yttrium (Y), zirconium (Zr), and palladium (Pd) are part of this group, revealing new characteristics and trends as we continue discovering.

5d Series: Advancing Deeper into the Table

Continuing our journey, the 5d series marks the filling of the next set of orbitals. Elements like hafnium (Hf), tantalum (Ta), and platinum (Pt) represent this stage, displaying unique properties and behaviors as we delve deeper into the periodic table.

6d Series: Beyond the Main Section

The 6d series encompasses elements situated beyond the main body of the periodic table. Elements like rutherfordium (Rf), dubnium (Db), and seaborgium (Sg) belong to this group, showcasing rare and distinct properties in this less commonly encountered orbital configuration.

(B)   Exceptions-

(a)  Above generalization has several exceptions because

         (i)   The energy difference between (n – 1)d and ns orbitals is very less.

        (ii) Half and completely filled sets of orbitals are relatively more stable.

(b) A consequence of this factor is reflected in the electronic configuration of following elements.

         (i)   In 3d series — Cr and Cu

        (ii) In 4d series — Nb, Mo, Tc, Ru, Rh, Pd, and Ag

        (iii) In 5d series — Pt and Au

        (iv)  In 6d series — Rg

(C)   Electronic configuration of all d-block elements.

(a)  3d-Series (First Transition Series)

(b) 4d Series (Second Transition Series)-

(c)  5d-Series (Third Transition series)

c)  6d-Series (Fourth Transition series)

2.0Atomic Radii of d Block Elements 

Period Trend:

• Initial five elements from Sc to Mn show decreasing atomic radius due to stronger nucleus-valence shell attraction over valence-penultimate shell repulsion.
• Fe, Co, and Ni maintain almost equal atomic radii as nucleus-valence shell attraction equals valence-penultimate shell repulsion.
• Cu to Zn exhibit increasing atomic radius due to weaker nucleus-valence shell attraction compared to valence-penultimate shell repulsion.

Group Trend:

• 4d series elements have larger atomic radii than 3d series.
• 4d and 5d series display nearly identical atomic radii owing to lanthanide contraction.

3.0Magnetic Properties of d Block Elements

Paramagnetism: Substances attracted to a magnetic field possess unpaired electrons in their atomic orbitals, termed paramagnetic substances. Transition metal ions or compounds with unpaired electrons in the d-subshell (configurations d1 to d9) typically exhibit paramagnetic behavior.

Diamagnetism: Substances repelled by a magnetic field, containing paired electrons in their atomic orbitals, are termed diamagnetic substances.

Paramagnetism in Metals: Metals with unpaired electrons typically display paramagnetism. 

• The magnetic moment (μ) for paramagnetic substances can be calculated using-

$\mu =\sqrt{(n(n+2))}$

• where 'n' is the number of unpaired electrons, measured in Bohr magneton units (B.M.).

Ferromagnetism: Some materials exhibit ferromagnetism, a robust form of paramagnetism, displaying very strong attraction to magnetic fields. Common ferromagnetic metals include iron (Fe), cobalt (Co), and nickel (Ni).

4.0Formation of Interstitial Compounds by d Block Elements 

• Interstitial compounds are formed when smaller atoms or molecules fit into the gaps or interstitial spaces between the larger atoms or ions in a crystal lattice. 
• In the case of d-block elements, these compounds can form when smaller atoms or molecules occupy the spaces between the atoms of the d-block metal lattice.

Characteristics and Examples:

• Titanium Carbide (TiC): TiC forms as carbon atoms occupy interstitial spaces in the crystal lattice of titanium. This compound displays exceptional hardness and is used in cutting tools and coatings.
• Manganese Nitride (Mn₄N): Mn₄N involves nitrogen atoms fitting into the interstitial spaces of manganese. It exhibits magnetic properties and is explored for potential applications in electronics and magnetic devices.
• Iron Hydride (Fe₃H): Fe₃H involves hydrogen occupying interstitial sites within iron. It's studied for its role in hydrogen storage and as a potential material for fuel cells.

5.0Formation of Alloys

The d-block elements, or transition metals, are pivotal in the formation of alloys due to their unique properties, allowing them to create materials with enhanced characteristics. Examples of Alloy Formation with d-Block Elements:

• Brass: A mixture of copper (Cu) and zinc (Zn), offering enhanced malleability and acoustic properties.
• Alnico Magnets: An alloy of aluminum (Al), nickel (Ni), and cobalt (Co), known for its strong magnetic properties.
• Titanium Alloys: Incorporating titanium (Ti) with elements like aluminum or vanadium for lightweight, corrosion-resistant materials used in aerospace and medical implants.

Some important alloys-

6.0Compounds Formed by d-block Elements 

Transition metal complexes occur when transition metals interact with ligands, which are molecules or ions that donate electrons, resulting in complex structures.

Here's an overview of the formation of complex compounds involving d-block elements:

1. Coordination Bonds:

• Central Metal Ion: A transition metal serves as the central ion in a coordination complex, surrounded by ligands.
• Ligands: These are molecules or ions with lone pairs or π-electrons that bond with the metal ion through coordinate covalent bonds, sharing electrons with the metal center.

2. Coordination Number and Geometry:

• Coordination Number: The number of bonds formed between the metal and its attached ligands determines the coordination number. It varies from 2 to 12 in most cases.
• Geometry: The arrangement of ligands around the metal ion determines the complex's geometry, such as octahedral, square planar, tetrahedral, or other shapes.

3. Ligand Exchange and Stability:

• Ligand Substitution: Transition metal complexes can undergo ligand exchange reactions, where one ligand is replaced by another, leading to different complex structures.
• Stability: The stability of these complexes is influenced by factors such as the nature of the metal ion, the type of ligands, and the overall charge of the complex.

4. Properties and Applications:

• Color: Transition metal complexes often exhibit vibrant colors due to the absorption and emission of specific wavelengths of light.
• Catalytic Activity: Many transition metal complexes serve as catalysts in various chemical reactions due to their ability to facilitate reactions by altering the reaction pathways.
• Biological Significance: Some metal complexes play essential roles in biological systems, acting as cofactors in enzymatic reactions or as therapeutic agents.

Examples of Transition Metal Complexes:

• [Fe(CN)₆]³⁻ : Hexacyanoferrate(III) ion, featuring iron (Fe) as the central metal ion bonded to six cyanide (CN⁻) ligands.
• [Cu(NH₃)₄]²⁺ : Tetraamminecopper(II) ion, with copper (Cu) coordinated to four ammonia (NH₃) ligands.
• [PtCl₄]²⁻ : Tetrachloridoplatinate(II) ion, containing platinum (Pt) coordinated to four chloride (Cl⁻) ligands.

7.0Catalytic Properties of d block Elements

• Transition metals, found in the d-block, make exceptional catalysts. They speed up chemical reactions without getting used up themselves. 
• These metals can activate molecules, facilitate bond-making and breaking, and enable various reactions, from hydrogenation to environmental processes like CO₂ conversion. They're vital in industries like petroleum refining, chemical production, and renewable energy, contributing to efficiency, selectivity, and sustainability in chemistry and technology.
• The density of d-block elements, or transition metals, varies widely based on their atomic masses, atomic radii, and crystal structures. 
• Generally, these metals tend to be denser than typical metals due to their relatively high atomic masses and tightly packed crystal lattices.

Transition metals often have densities ranging from around 2 to 22 grams per cubic centimeter (g/cm³). For instance:

 Sc < Ti < V < Cr < Mn < Fe < Co < Ni = Cu > Zn

 (Zn has a lower density because of its large atomic volume.)

Minimum density in 3d series → Sc

Maximum density in 3d series → Ni and Cu

In Group : 3d < 4d < 5d

Elements with the highest densities are- 

Osmium (Os) = 22.51 g/cm³, Iridium (Ir) = 22.61 g/cm³

8.0Oxidation States of d block Elements

The d-block, or transition metals, exhibit various oxidation states due to their unique electronic configurations that allow them to lose or gain electrons from their d-orbitals. Here's an overview of their oxidation states:

1. Variable Oxidation States:

• Transition metals can adopt multiple oxidation states, often due to the availability of different numbers of electrons in their d-orbitals. These oxidation states typically range from +1 to +8, though some metals can go beyond these limits.

2. Common Oxidation States:

• Lower Oxidation States: Many transition metals exhibit lower oxidation states, such as +1, +2, or +3. For example, iron (Fe) commonly forms ions with +2 and +3 oxidation states.
• Higher Oxidation States: Some transition metals can achieve higher oxidation states, like +4, +5, +6, or even higher. Manganese (Mn), for instance, can form compounds with oxidation states ranging from +2 to +7.

3. Factors Influencing Oxidation States:

• Electronic Configurations: The number of electrons in the outermost d-orbitals determines the possible oxidation states for a transition metal.
• Chemical Environment: The presence of ligands or the nature of the chemical surroundings can influence the stability of different oxidation states.

Example:-

In Ni(CO)₄ and Fe(CO)₅, the oxidation state of nickel and iron is zero.

They show variable oxidation states.

 Note-  Underlined states are the most stable ones.

9.0Formation of Colored Compound

Transition metals in the d-block exhibit vibrant colors in their ions due to the presence of partially filled d-orbitals, which undergo electronic transitions when absorbing light. Here's a concise overview:

Formation of Colored Ions:

• d-orbital Configurations: Transition metal ions often have partially filled d-orbitals due to their variable oxidation states. Electrons in these orbitals can absorb specific wavelengths of light, leading to the display of colors.
• Electronic Transitions: When visible light interacts with these ions, electrons move between different energy levels within the d-orbitals. Absorption of certain wavelengths causes electrons to jump from lower to higher energy levels, leading to the observed colors.
• Color Characteristics: The specific color observed depends on the energy difference between the d-orbital electronic levels. Different transition metals or oxidation states display distinct colors due to their unique electronic structures.

Examples of Colored Ions:

• Copper (Cu²⁺): Forms blue-colored ions due to the d-orbital transitions involving its partially filled orbitals.
• Chromium (Cr³⁺): Yields green-colored ions attributed to its d-orbital transitions.

10.0Important Compound of d-block

Potassium Dichromate (K₂Cr₂O₇)

Preparation- Potassium dichromate (K₂Cr₂O₇) is commonly prepared through the reaction between sodium dichromate (Na₂Cr₂O₇) and potassium chloride (KCl) in an aqueous solution. The balanced chemical equation for this reaction is:

${\mathrm{Na}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+2\mathrm{KCl}\to {\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+2\mathrm{NaCl}$

This method involves the exchange of ions between sodium dichromate and potassium chloride in a solution, resulting in the formation of potassium dichromate and sodium chloride as a byproduct. The potassium dichromate can then be isolated by crystallization.

Potassium dichromate (K₂Cr₂O₇) possesses several important properties that make it valuable in various applications:

• Oxidizing Agent: It is a powerful oxidizing agent, used in numerous oxidation reactions due to its ability to provide oxygen or accept electrons.
• Color: Potassium dichromate appears as bright orange-red crystals or powder, making it easily identifiable.
• Solubility: It is soluble in water, forming a vibrant orange solution. This solubility aids its use in various solutions and applications.
• Chemical Stability: It exhibits good stability under normal conditions, but it decomposes when exposed to heat or when in contact with reducing agents.
• Other Applications: Potassium dichromate finds use in various industries:
• • Laboratory and Analytical Chemistry: Used in qualitative analysis and titrations as an oxidizing agent.
  • Photography: Historically used in old photographic processes.
  • Manufacturing: Employed in the production of pigments, dyes, and inorganic chemicals.
  • Wood Preservation: Utilized to treat wood, acting as a biocide to protect against decay.
• Toxicity: It is highly toxic and carcinogenic. Inhalation or ingestion can cause severe health issues. Due to its toxicity, its use is restricted or regulated in many countries.

Potassium Permanganate (KMnO₄)

Preparation- Potassium permanganate (KMnO₄) is typically prepared through the reaction between manganese dioxide (MnO₂) and potassium hydroxide (KOH) in the presence of an oxidizing agent like potassium chlorate (KClO₃) or potassium nitrate (KNO₃).

The preparation involves several steps:

• Step 1. Conversion of Manganese Dioxide (MnO₂): 

Manganese dioxide is reacted with a hot concentrated solution of potassium hydroxide (KOH) in the presence of an oxidizing agent (such as potassium chlorate or potassium nitrate). 

This reaction produces potassium manganate (K₂MnO₄).        

2MnO₂  + 4KOH + O₂   →  2K₂MnO4​   +  2H_2​O

• Step 2. Conversion to Potassium Permanganate: 

The potassium manganate (K₂MnO₄) formed in the first step is then converted to potassium permanganate (KMnO₄) by adding an acid, usually sulfuric acid (H₂SO₄), which oxidizes the manganate ion to permanganate ion.

3K₂MnO₄ + 4H₂SO₄   →    2KMnO₄ + 2MnSO₄ ​+ K₂SO₄ + 4H₂O

After this process, the resulting solution contains potassium permanganate, which can be isolated by crystallization or other purification methods.

Applications of Potassium Permanganate (KMnO₄)- KMnO₄ is a powerful oxidizing agent and chemical compound. 

It appears as dark purple crystals or a powder and is commonly used for various purposes:

• Water Treatment: It's used to remove impurities and odors from water due to its oxidizing properties. It can help in treating water for drinking and industrial purposes.
• Antiseptic: In a diluted form, it can be used as an antiseptic to clean wounds, disinfect surfaces, or treat certain skin conditions like dermatitis and fungal infections.
• Chemical Reactions: Potassium permanganate is a strong oxidizing agent and is involved in various chemical reactions in laboratories and industries. It's used in the synthesis of organic compounds and as an oxidizer in chemical reactions.
• Analytical Chemistry: It's employed as a reagent in qualitative analysis to identify compounds, especially those containing reducing agents.