The d - and f - Block Elements — Class 12 Chemistry Notes

Topics covered in The d - and f - Block Elements

1. 1.Introduction of d & f Block Elements

   Short Answer

   The d-block elements are known as transition metals and include elements in groups 3 to 12 of the periodic table. They are characterized by their ability to form colorful compounds, variable oxidation states, and conduct electricity and heat. The f-block elements are known as inner transition metals and include the lanthanides and actinides. They are essential in various technologies like electronics, magnets, and nuclear reactors.

   Long Answer

   Introduction to d-block Elements:
   

   The d-block elements, also known as transition metals, occupy the center of the periodic table, specifically groups 3 to 12. These elements have partially filled d orbitals in their atoms or ions. Characteristics of d-block elements include the formation of colorful compounds, the ability to exist in various oxidation states, and excellent conductivity of heat and electricity. They are widely used in industry for catalysis, as well as in making alloys and colorful pigments.

   Key Features of d-block Elements:

   1. Variable Oxidation States: Transition metals can exhibit multiple oxidation states, which allows them to form a variety of compounds.
   2. Formation of Colored Compounds: Due to the d-d transition of electrons, many d-block elements form colorful compounds, useful in making pigments and dyes.
   3. Conductivity: These elements are good conductors of heat and electricity, making them valuable in electrical applications.
   4. Catalytic Properties: Many transition metals and their compounds act as catalysts in chemical reactions, speeding up the process without being consumed.

   Introduction to f-block Elements:
   The f-block elements, known as inner transition metals, include the lanthanides and actinides. They are located in two rows at the bottom of the periodic table. These elements have partially filled f orbitals. The lanthanides are known for their strong magnetic properties and are used in making powerful magnets, lasers, and in various other electronics. The actinides include elements that are primarily radioactive, such as uranium and thorium, which are critical for nuclear energy and weapons.

   Key Features of f-block Elements:

   1. Radioactivity: Many actinides are radioactive and are used in nuclear reactors and for medical imaging.
   2. Magnetic Properties: Lanthanides have unique magnetic properties, making them essential in manufacturing strong magnets for motors and hard drives.
   3. Colorful Compounds: Similar to d-block elements, some f-block elements also form colorful compounds, though their use is more specialized.
   4. Use in Electronics: Due to their unique properties, lanthanides are used in various electronic devices, including smartphones and computers.

   Real-Life Applications and Industries:

   • Electronics: Both d and f block elements are used in making components for electronic devices, such as semiconductors and displays.
   • Catalysis: Transition metals are widely used as catalysts in the chemical industry, for example, in the production of ammonia and plastics.
   • Energy: Actinides, like uranium and thorium, are used as fuel in nuclear reactors.
   • Medicine: Some transition metals are used in medical imaging and treatment, such as gadolinium in MRI contrast agents.

2. 2.The Transition Elements (d-block) - Position in the Periodic Table and Electronic Configurations of the d-Block Elements

   Short Answer

   The transition elements, or d-block elements, are located in the center of the Periodic Table from groups 3 to 12. Their electronic configurations typically involve the filling of d-orbitals, ranging from 33d to 66d. The general electronic configuration is [ ](−1)1−100−2[Noble gas](n−1)d1−10ns0−2, where n represents the principal quantum number of the outermost shell.

   Long Answer

   Position in the Periodic Table

   The Periodic Table is organized in such a way that it reflects the electronic structure of the atoms of the elements, allowing for the prediction of chemical, physical, and atomic properties. The transition elements occupy a unique position in the center of the Periodic Table, specifically in groups 3 through 12. This central positioning is not arbitrary but is due to their distinctive electronic configurations, which involve the d subshell.

   Electronic Configurations of the d-Block Elements

   To understand the electronic configurations of the d-block elements, it's crucial to delve into the concept of atomic orbitals. Electrons in an atom are arranged in various orbitals around the nucleus, and these orbitals are grouped into different energy levels or shells. The d-block elements are characterized by the filling of their d-orbitals, which are one level below the atom's outermost shell.

   The general electronic configuration for these elements can be expressed as [ ](−1)1−100−2[Noble gas](n−1)d1−10ns0−2, where:

   • [ ][Noble gas] represents the electron configuration of the nearest noble gas preceding the element in the Periodic Table, acting as a shorthand to simplify the notation.
   • (−1)1−10
     (n−1)d1−10 indicates the filling of the d-orbitals. The −1n−1 suggests that these d-orbitals belong to the penultimate (one before the last) energy level. The superscript 1−101−10 shows that these orbitals can hold between 1 and 10 electrons.
   • 0−2
     ns0−2 indicates that the s-orbital of the outermost shell (principal quantum number n) can be empty or contain up to 2 electrons.

   Real-Life Examples and Applications

   Colorful Compounds

   The transition metals form a variety of colorful compounds, which is attributable to the electronic transitions within the d-orbitals. These transitions absorb specific wavelengths of light, which is why compounds like copper sulfate (bright blue) and potassium permanganate (purple) are colored. This property is utilized in creating pigments and dyes for various applications, from art to industrial design.

   Catalysis

   Transition elements are renowned for their catalytic properties. For instance, iron acts as a catalyst in the Haber process for synthesizing ammonia from nitrogen and hydrogen. This process is crucial for producing fertilizers, which in turn supports global agriculture. Similarly, platinum and palladium are used as catalysts in catalytic converters to reduce harmful emissions from vehicles.

   Careers and Industries

   Understanding the properties and applications of transition elements opens doors to numerous career paths and industries:

   • Chemistry and Biochemistry: Professionals in these fields explore the chemical behaviors of transition metals, including their roles in biological systems, such as the importance of iron in hemoglobin for oxygen transport in blood.
   • Materials Science: Experts in materials science develop new materials with enhanced properties for use in technology, construction, and manufacturing. Transition metals play a crucial role in alloys, superconductors, and semiconductors.
   • Environmental Science: Knowledge of transition metals is vital for addressing environmental challenges, including pollution control and the development of green catalytic processes.

   Understanding the transition elements and their electronic configurations is foundational in chemistry, providing insights into the behavior of these elements and their role in the natural and technological world.

3. 3.General Properties of the Transition Elements (d-Block)

   Short Answer:

   Transition elements exhibit unique properties due to the filling of d-orbitals. These include variable oxidation states, formation of colored ions, magnetic properties, high melting and boiling points, formation of complex compounds, catalytic properties, and the ability to form alloys and interstitial compounds.

   Long Answer: 1. Physical Properties:

   High Melting and Boiling Points: The strong metallic bonds in transition metals, facilitated by the delocalization of d electrons, contribute to their high melting and boiling points. For instance, Tungsten (W) has one of the highest melting points of all elements, around 3422°C, which is why it's used in light bulb filaments.

   2. Variation in Atomic and Ionic Sizes:

   The size of atoms and ions generally decreases across a period due to the increase in nuclear charge, which pulls the electrons closer to the nucleus. However, the decrease is not as significant in transition metals compared to s-block elements, due to the shielding effect of the inner d electrons.

   3. Ionisation Enthalpies:

   Ionisation enthalpy is the energy required to remove an electron from an atom or ion. In transition metals, these values are higher than s-block elements but vary less across a period. This is because, although nuclear charge increases, so does electron-electron repulsion in the similarly sized d-orbitals, somewhat balancing out the effect.

   4. Oxidation States:

   Transition metals exhibit a variety of oxidation states due to the relatively low energy difference between their outer s and d orbitals, allowing for the loss of electrons from both. For example, manganese (Mn) shows all oxidation states from +2 to +7, facilitating its role in different chemical reactions, including acting as an oxidizing agent in KMnO₄.

   5. Trends in 2+/M2+/M and 3+/2+M3+/M2+ Standard Electrode Potentials:

   The standard electrode potentials are indicators of a metal's ability to be oxidized or reduced. Early transition metals tend to have more negative Eo values for 2+/M2+/M, indicating a greater tendency to lose electrons and be oxidized. For 3+/2+M3+/M2+, the potentials become more positive as we move from left to right across the period, suggesting an increasing preference for the +3 oxidation state due to effective nuclear charge.

   6. Chemical Reactivity and Eo Values:

   Chemical reactivity in transition metals varies widely, influenced by their electrode potentials. Metals with lower Eo values are more reactive and readily oxidized. For example, Zinc (Zn) with a standard reduction potential of -0.76 V for 2+/Zn2+/Zn is more reactive than Copper (Cu) with =+0.34Eo=+0.34V for 2+/Cu2+/Cu.

   7. Magnetic Properties:

   Transition metals can be paramagnetic or diamagnetic, depending on the presence of unpaired d electrons. The magnetic moment (μ) can be calculated using the formula =(+2)μ=n(n+2)​ Bohr magnetons, where n is the number of unpaired electrons. For example, Fe3+3+ has 5 unpaired electrons, giving it a relatively high magnetic moment.

   8. Formation of Coloured Ions:

   The color in transition metal ions is due to electronic transitions between d orbitals split by the crystal field. The specific wavelength of light absorbed (and thus the color observed) depends on the energy gap between these levels. For example, the [Cu(H2O)6]2+2+ ion is blue due to the absorption of light in the red region.

   9. Formation of Complex Compounds:

   Transition metals form complex compounds due to their ability to accept electrons into their d orbitals. The ligand field stabilization energy (LFSE) concept helps in understanding the stability of these complexes. For example, the formation of the hexacyanoferrate(II) ion, [6]4−[Fe(CN)6​]4−, involves strong field ligands (CN−−) that lead to a large LFSE, making the complex very stable.

   10. Catalytic Properties:

   Transition metals and their compounds exhibit catalytic properties due to their ability to adopt multiple oxidation states and to form complexes. A classic example is the use of nickel in the hydrogenation of alkenes, where Ni temporarily bonds with H2, facilitating its addition to the alkene.

   11. Formation of Interstitial Compounds:

   Transition metals can incorporate small atoms like H, C, or N into interstitial spaces within their crystal lattice, significantly altering physical properties. For example, the addition of carbon to iron forms steel, dramatically increasing its strength compared to pure iron.

   12. Alloy Formation:

   Alloys are mixtures of metals that often include transition metals due to their ability to dissolve other metals. For instance, stainless steel is an alloy primarily of iron, chromium, and nickel. The chromium provides corrosion resistance, while nickel adds toughness and strength.

   Reaction Examples:

   Formation of Coloured Ions: [Fe(H2O)6]3+→[Fe(H2O)6]2++e−[Fe(H2​O)6​]3+→[Fe(H2​O)6​]2++e− (light absorption results in color)

   Catalytic Property Example: Haber process: 2+32⟷Fe catalyst23N2​+3H2​⟷Fe catalyst​2NH3​ (iron facilitates the reaction at lower temperatures)

   These properties and examples illustrate the complex and varied nature of transition metals, underpinning their essential roles in chemistry and technology.

4. 4.Some Important Compounds of Transition Elements

   Short Answer:

   Some important compounds of transition elements include oxides, oxoanions, potassium dichromate (227K2​Cr2​O7​), and potassium permanganate (4KMnO4​). These compounds are characterized by their oxidation states, reactivity, and the ability to act as oxidizing agents. Potassium dichromate is used in the leather industry and for preparing azo compounds, while potassium permanganate is known for its oxidizing properties in organic chemistry and volumetric analysis.

   Long Answer:

   Oxides and Oxoanions of Metals:

   • Formation: Transition metals react with oxygen at high temperatures to form oxides. Most metals form ionic MO oxides, with their highest oxidation states corresponding to their group numbers, ranging from 23Sc2​O3​ to 27Mn2​O7​.
   • Ionic Character: As the oxidation state of a metal increases, its oxides' ionic character decreases, shifting towards covalency. For example, 27Mn2​O7​ is a covalent compound and behaves as a green oil.
   • Acidic Character: Higher oxides tend to have acidic character. 27Mn2​O7​ forms 4HMnO4​, 3CrO3​ gives 24H2​CrO4​ and 227H2​Cr2​O7​, and 25V2​O5​ is mainly acidic but also amphoteric, forming 43−VO43−​ and 2+VO2+​ salts.

   Potassium Dichromate (227K2​Cr2​O7​):

   • Preparation: Obtained from the fusion of chromite ore (24FeCr2​O4​) with sodium or potassium carbonate, followed by acidification to form sodium dichromate, which is then treated with potassium chloride to produce 227K2​Cr2​O7​.
   • Properties and Use: It is a strong oxidizing agent, used extensively in the leather industry, preparation of azo compounds, and as a primary standard in volumetric analysis.
   • Oxidizing Actions: In acidic solutions, it can oxidize iodides to iodine, sulphides to sulphur, tin(II) to tin(IV), and iron(II) salts to iron(III).

   Potassium Permanganate (4KMnO4​):

   • Preparation: Produced by fusing 2MnO2​ with an alkali metal hydroxide and an oxidizing agent like 3KNO3​, leading to 24K2​MnO4​ which disproportionates in neutral or acidic solution to give 4KMnO4​.
   • Properties and Use: 4KMnO4​ forms dark purple crystals and is used as an oxidizing agent in organic chemistry, and for volumetric analysis.
   • Oxidizing Actions: It oxidizes oxalates to carbon dioxide, iron(II) to iron(III), nitrites to nitrates, and iodides to free iodine in acid solutions. In neutral or slightly alkaline solutions, it can oxidize iodides to iodates and thiosulfates to sulfates.

   These compounds demonstrate the versatility and reactivity of transition metals in various oxidation states, making them invaluable in industrial processes, analytical chemistry, and environmental applications.

5. 5.The Inner Transition Elements ( f-block)

   Short Answer:

   The inner transition elements, or f-block elements, comprise the lanthanoids (lanthanides) and actinoids (actinides). Lanthanoids have electronic configurations typically featuring 4f electrons, while actinoids primarily involve 5f electrons. Both series display variability in oxidation states, usually +3 for lanthanoids and ranging from +3 to +6 (and sometimes higher) for actinoids. Lanthanoids are known for their similarities across the series, including small and gradually decreasing atomic and ionic sizes—termed the lanthanide contraction. Actinoids show more diversity in their chemical properties and greater complexity in their electronic configurations due to the involvement of 5f electrons, which are more shielded and extend farther from the nucleus compared to 4f electrons.

   Long Answer:

   The f-block elements, known as the inner transition metals, are divided into two series: the lanthanoids (lanthanide series) and the actinoids (actinide series). These elements are characterized by the filling of their 4f and 5f orbitals, respectively. Their unique electronic configurations lead to distinct physical and chemical properties.

   Lanthanoids (Lanthanide Series):

   Electronic Configurations: The lanthanoids have electronic configurations that typically begin with []41−1450−162[Xe]4f1−145d0−16s2. This configuration indicates that the 4f orbitals are being filled as one progresses through the series from Lanthanum (La) to Lutetium (Lu). The filling of 4f orbitals imparts specific chemical properties to these elements.

   Atomic and Ionic Sizes: Across the lanthanoid series, there is a noticeable decrease in atomic and ionic radii, a phenomenon known as the lanthanide contraction. This contraction occurs because the additional electrons enter the 4f orbital, which does not shield the increasing nuclear charge effectively. As a result, the outer electrons are pulled closer to the nucleus, leading to a decrease in size. The lanthanide contraction affects the chemistry of the lanthanoids by increasing their density, melting point, and boiling point as one moves from La to Lu.

   Oxidation States: Lanthanoids predominantly exhibit a +3 oxidation state, which corresponds to the loss of the 6s and one 4f electron. However, some elements can also exhibit +2 or +4 oxidation states under certain conditions. This variability in oxidation states contributes to the lanthanoids' diverse chemistry.

   General Characteristics:

   • Magnetic Properties: Many lanthanoids have unpaired f electrons, leading to notable magnetic properties.
   • Coloration: Compounds of lanthanoids are often colorful due to electronic transitions within the 4f orbitals.
   • Catalytic Properties: Several lanthanoids serve as effective catalysts in various chemical reactions.
   • Applications: They are widely used in manufacturing catalysts, magnets, phosphors for color television tubes and LED lights, and as additives in steel to improve its properties.

   Actinoids (Actinide Series):

   Electronic Configurations: Actinoids have electronic configurations in the form []51−1460−172[Rn]5f1−146d0−17s2, indicating the filling of 5f orbitals. The 5f orbitals participate more actively in chemical bonding compared to 4f orbitals in lanthanoids. This participation leads to more complex chemistry for actinoids.

   Atomic and Ionic Sizes: Like the lanthanoids, actinoids also experience a decrease in ionic size across the series, known as the actinide contraction. However, the effect is somewhat less pronounced than in lanthanoids due to the greater radial extension of the 5f orbitals which can more effectively shield the increasing nuclear charge.

   Oxidation States: Actinoids exhibit a broader range of oxidation states compared to lanthanoids, typically from +3 to +6, with some elements like Uranium (U) and Plutonium (Pu) showing states up to +7. This range is due to the relatively low energy gap between the 5f, 6d, and 7s orbitals, allowing more electrons to participate in bonding.

   General Characteristics and Comparison with Lanthanoids:

   • Reactivity: Actinoids are generally more reactive than lanthanoids, especially the earlier members of the series.
   • Chemical Diversity: The actinoids show greater chemical diversity due to their variable oxidation states and the involvement of 5f electrons in bonding.
   • Radioactivity: All actinoids are radioactive, with many being synthetic elements produced in nuclear reactors or particle accelerators. Their radioactivity has significant implications for their handling and applications.
   • Applications: Actinoids are crucial in nuclear energy as fuel (e.g., 235235U and 239239Pu) and in the production of nuclear weapons. They also have uses in smoke detectors (Americium) and as sources of thermal power in space probes (Plutonium).

   In summary, the lanthanoids and actinoids differ significantly in their electronic configurations, resulting in distinct chemical behaviors. The lanthanoids are primarily characterized by their uniform +3 oxidation state and the lanthanide contraction, leading to applications in technology and manufacturing. In contrast, the actinoids' chemistry is marked by a wider range of oxidation states and significant radioactivity, making them critical in nuclear science and technology.

6. 6.Some Applications of d- and f-Block Elements

   Short Answer:

   d- and f-block elements, encompassing the transition metals and the lanthanides and actinides respectively, play crucial roles in various industrial, technological, and medical fields. Transition metals are widely used in catalysis, electronics, and alloy formation due to their versatile oxidation states and electronic properties. Lanthanides find applications in electronics, lighting, and magnets, while actinides are primarily used in nuclear energy and radiomedicine due to their radioactive properties.

   Long Answer:

   Applications of d-Block Elements (Transition Metals):

   1. Catalysis: Transition metals and their compounds act as catalysts in industrial processes. For instance, nickel catalyzes the hydrogenation of unsaturated fats and oils, and iron is a key catalyst in the Haber process for ammonia synthesis.

   2. Electronics and Alloys: Transition metals like copper and gold are essential in electronics for their excellent conductivity. Alloys such as steel (iron and carbon) and brass (copper and zinc) have enhanced mechanical properties and corrosion resistance, making them invaluable in construction and engineering.

   3. Coinage and Jewelry: Gold, silver, and platinum are widely used in coinage, jewelry, and decorative items due to their luster, rarity, and resistance to tarnishing.

   4. Medicinal Applications: Certain transition metals play roles in medicine; for example, platinum compounds like cisplatin are used in chemotherapy to treat cancer.

   Applications of f-Block Elements:

   Lanthanides (Lanthanoid Series):

   1. Electronics and Optics: Rare earth elements are crucial in manufacturing high-performance magnets used in wind turbines, hard drives, and electric vehicles (e.g., neodymium magnets). Europium and terbium are used in fluorescent and LED lighting, and yttrium aluminum garnet (YAG) lasers.

   2. Catalysts: Lanthanides act as catalysts in petroleum refining and in the production of synthetic organic compounds.

   3. Glass and Ceramics: Certain lanthanides are used to improve the properties of glass and ceramics, adding color or mechanical strength. For example, lanthanum is used in camera and telescope lenses to improve clarity.

   Actinides (Actinoid Series):

   1. Nuclear Energy: Uranium and plutonium are key fuels for nuclear reactors, with uranium-235 and plutonium-239 being the most widely used isotopes for fission reactions in nuclear power plants.

   2. Radioisotopes in Medicine: Actinides like americium-241 are used in smoke detectors for their ionizing radiation. Others, such as thorium-232, are under research for potential use in targeted alpha therapy (TAT) in cancer treatment.

   3. Space Exploration: Plutonium-238 is used as a power source in radioisotope thermoelectric generators (RTGs) for space missions, providing electricity and heat to spacecrafts and rovers exploring distant planets and moons.

   In summary, d- and f-block elements are integral to modern society, contributing to advancements in technology, energy, and medicine. Their unique properties enable them to be used in a wide range of applications, from everyday items like electronics and jewelry to critical uses in nuclear energy and space exploration.