65d ago

The d- and f- Block Elements

d-Block Elements

  • Located in Groups 3-12 of the periodic table.

  • Characterized by the progressive filling of d orbitals, influencing their chemical properties.

  • Exhibit metallic properties such as high tensile strength, ductility, malleability, with good thermal and electrical conductivity.

  • Often form colored ions and display variable oxidation states due to the involvement of d electrons in chemical bonding.

  • Divided into four transition metal series: 3d (Sc to Zn), 4d (Y to Cd), 5d (La, Hf to Hg), and 6d (Ac, Rf to Cn).

f-Block Elements

  • Positioned in a separate panel at the bottom of the periodic table to maintain the periodic table's structure.

  • Distinguished by the progressive filling of 4f and 5f orbitals.

  • Comprise two inner transition metal series: lanthanoids (4f series, Ce to Lu) and actinoids (5f series, Th to Lr).

  • Many actinoids are radioactive, with significant roles in nuclear applications and research.

Transition Metals

  • Defined by IUPAC as elements having an incomplete d subshell in neutral atoms or their ions.

  • Term originally denoted elements with properties intermediate between s- and p-block elements.

  • Exhibit a wide range of chemical behaviors, including catalytic activity and the formation of complex ions.

  • Group 12 elements—zinc, cadmium, and mercury—possess a complete d10d^{10}$$d^{10}$$ configuration and are generally excluded from the transition metals category but are often studied alongside them due to similar chemical behaviors.

Inner Transition Metals

  • Consist of the lanthanoids (cerium to lutetium) and actinoids (thorium to lawrencium).

  • Actinoids, such as thorium, protactinium, and uranium, are vital as sources of nuclear energy.

  • Lanthanoids are used in various applications, including magnets, catalysts, and phosphors.

Electronic Configuration

  • Follow a general electronic configuration of (n1)d110ns12(n-1)d^{1-10} ns^{1-2}$$(n-1)d^{1-10} ns^{1-2}$$, with exceptions like palladium (Pd), which has a 4d105s04d^{10}5s^0$$4d^{10}5s^0$$ configuration.

  • Deviations from the general configuration arise due to minimal energy differences between (n1)d(n-1)d$$(n-1)d$$ and nsns$$ns$$ orbitals.

  • Stability of half-filled and completely filled d orbitals significantly influences electronic configurations.

  • Noteworthy examples:

    • Chromium (Cr): 3d54s13d^5 4s^1$$3d^5 4s^1$$ instead of 3d44s23d^4 4s^2$$3d^4 4s^2$$.

    • Copper (Cu): 3d104s13d^{10} 4s^1$$3d^{10} 4s^1$$ instead of 3d94s23d^9 4s^2$$3d^9 4s^2$$.

  • Zinc (Zn), cadmium (Cd), mercury (Hg), and copernicium (Cn) have a (n1)d10ns2(n-1)d^{10} ns^2$$(n-1)d^{10} ns^2$$ configuration and are not considered transition elements due to their completely filled d orbitals.

Properties of Transition Elements

  • Display a diverse array of oxidation states, facilitating their participation in numerous chemical reactions.

  • Commonly form colored ions as a result of electronic transitions within the d orbitals.

  • Exhibit a propensity for complex formation with ligands, leading to a variety of coordination compounds.

  • Act as effective catalysts in various industrial processes.

  • Demonstrate paramagnetic behavior due to unpaired electrons in their d orbitals.

  • Exhibit similarities within horizontal rows, reflecting gradual changes in electronic structure.

Physical Properties

  • Characterized by metallic attributes, including high tensile strength, ductility, malleability, and excellent thermal and electrical conductivity.

  • Exceptions include zinc, cadmium, mercury, and manganese, which deviate from typical metallic behavior to varying degrees.

  • Generally hard (excluding Zn, Cd, and Hg) with low volatility, making them suitable for structural applications.

  • Exhibit high melting and boiling points due to the involvement of (n1)d(n-1)d$$(n-1)d$$ and nsns$$ns$$ electrons in metallic bonding.

  • Melting points typically peak at d5d^5$$d^5$$ (except for Mn and Tc) and decrease with increasing atomic number.

Enthalpy of Atomization

  • Exhibit high enthalpies of atomization, indicating strong metallic bonding.

  • Enthalpies generally peak in the middle of each transition series, corresponding to maximum unpaired d electrons.

  • Stronger bonding is associated with a greater number of valence electrons.

  • Metals with high enthalpies of atomization tend to be chemically noble.

  • Second and third series elements generally have greater enthalpies of atomization compared to first series elements, reflecting stronger metallic bonding.

Atomic and Ionic Sizes

  • Ions with the same charge exhibit a progressive decrease in radius with increasing atomic number due to ineffective d electron shielding, increasing electrostatic attraction.

  • Atomic radii decrease similarly across each series.

  • Increase from the 3d to 4d series, but the 5d series radii are similar to the 4d series because of the lanthanoid contraction.

Lanthanoid Contraction

  • Caused by the filling of 4f orbitals before the 5d orbitals, leading to a regular decrease in atomic radii.

  • Compensates for the expected increase in atomic size down the group.

  • Results in similar radii for 4d and 5d series elements such as zirconium (Zr) and hafnium (Hf).

  • Imperfect shielding of 4f electrons results in a regular decrease in size with increasing nuclear charge.

Density

  • Increases from titanium (Z = 22) to copper (Z = 29) due to the decrease in metallic radius and increase in atomic mass.

Ionization Enthalpies

  • Increase along each series as a result of increasing nuclear charge.

  • Successive enthalpies do not increase as steeply as non-transition elements due to d-electron shielding.

  • Variation is less pronounced compared to non-transition elements.

  • When d-block elements form ions, ns electrons are generally lost before (n1)d(n – 1) d$$(n – 1) d$$ electrons.

  • Second ionization enthalpy increases with effective nuclear charge.

  • Breaks in trend observed at Mn2+ and Fe3+ due to stable d5d^5$$d^5$$ configurations.

Exchange Energy

  • Stabilizes energy states and is proportional to the number of pairs of parallel spins.

  • Loss of exchange energy increases stability, making ionization more difficult.

  • The lowest common oxidation state is +2.

Oxidation States

  • Transition elements exhibit a variety of oxidation states, allowing them to form numerous compounds.

  • Elements in the middle of the series (e.g., Mn) display the greatest number of oxidation states.

  • Fewer oxidation states are observed at the extreme ends of the series (Sc, Ti, Cu, Zn).

  • Maximum oxidation states up to Mn correspond to the sum of s and d electrons.

  • Variability in oxidation states arises from the incomplete filling of d orbitals.

  • Higher oxidation states are favored by heavier members in the d-block (e.g., Mo(VI) and W(VI) are more stable than Cr(VI)).

  • Low oxidation states are stabilized by ligands with π\pi$$\pi$$-acceptor character (e.g., Ni(CO)4, Fe(CO)5).

Standard Electrode Potentials

  • Copper's unique behavior (positive EoE^o$$E^o$$) prevents it from liberating H2H_2$$H_2$$ from acids.

  • General trend towards less negative EoE^o$$E^o$$ values across the series is related to increasing ionization enthalpies.

  • Values for Mn, Ni, and Zn are more negative than expected.

  • Stability of the half-filled d5d^5$$d^5$$ subshell in Mn2+ and the completely filled d10d^{10}$$d^{10}$$ configuration in Zn2+ influence EoE^o$$E^o$$ values.

  • EoE^o$$E^o$$ for Ni is related to the highest negative \Delta[hyd}H^o$$\Delta[hyd}H^o$$.

Stability of Higher Oxidation States

  • Highest oxidation numbers achieved in $$TiX4,, $$, $$VF5,and, and $$, and $$CrF_6$$.

  • Fluorine stabilizes higher oxidation states due to its high lattice energy or bond enthalpy.

  • Oxygen stabilizes high oxidation states in oxides and oxocations (e.g., VO2+,VO2+,TiO2+VO_2^+, VO^{2+}, TiO^{2+}$$VO_2^+, VO^{2+}, TiO^{2+}$$).

  • Oxygen’s ability to form multiple bonds contributes to its superiority.

Chemical Reactivity

  • Transition metals vary in chemical reactivity.

  • Most are electropositive and dissolve in mineral acids.

  • First series metals (except Cu) are more reactive.

  • Formation of divalent cations decreases across the series.

  • Mn3+Mn^{3+}$$Mn^{3+}$$ and Co3+Co^{3+}$$Co^{3+}$$ are the strongest oxidizing agents.

  • Ti2+Ti^{2+}$$Ti^{2+}$$, V2+V^{2+}$$V^{2+}$$, and Cr2+Cr^{2+}$$Cr^{2+}$$ are strong reducing agents.

Magnetic Properties

  • Diamagnetic substances are repelled, while paramagnetic substances are attracted to magnetic fields.

  • Ferromagnetism is an extreme form of paramagnetism.

  • Paramagnetism arises from unpaired electrons.

  • Magnetic moment (μ)=n(n+2)(\mu) = \sqrt{n(n+2)}$$(\mu) = \sqrt{n(n+2)}$$ where n is the number of unpaired electrons.

Formation of Colored Ions

  • Excitation of electrons from lower to higher energy d orbitals.

  • Energy of excitation corresponds to the frequency of light absorbed, typically in the visible region.

  • Color observed corresponds to the complementary color of light absorbed.

  • Frequency depends on the nature of the ligand, affecting the crystal field splitting.

Trends in the M3+/M2+ Standard Electrode Potentials

  • Low value for Sc reflects the stability of Sc3+Sc^{3+}$$Sc^{3+}$$ (noble gas configuration).

  • High value for Zn due to electron removal from the stable d10d^{10}$$d^{10}$$ configuration of Zn2+Zn^{2+}$$Zn^{2+}$$.

  • High value for Mn shows the stability of Mn2+Mn^{2+}$$Mn^{2+}$$ (d5d^5$$d^5$$).

  • Low value for Fe shows the stability of Fe3+Fe^{3+}$$Fe^{3+}$$ (d5d^5$$d^5$$).

  • Low value for V is related to the stability of V2+V^{2+}$$V^{2+}$$ (half-filled t2gt_{2g}$$t_{2g}$$ level).

Formation of Complex Compounds

  • Metal ions bind anions or neutral molecules to form complex species.

  • Transition metals form a large number of complexes due to their smaller sizes, high ionic charges, and availability of d orbitals.

Catalytic Properties

  • Transition metals and their compounds exhibit catalytic activity.

  • This is due to their ability to adopt multiple oxidation states and form complexes.

  • Examples include $$V2O5$$ (Contact Process), finely divided iron (Haber’s Process), and nickel (Catalytic Hydrogenation).

  • Catalysis involves bond formation between reactant molecules and catalyst surface atoms, increasing reactant concentration, and weakening bonds, thereby lowering the activation energy.

Formation of Interstitial Compounds

  • Small atoms (H, C, N) trapped inside the crystal lattices of metals.

  • These compounds are non-stoichiometric, neither ionic nor covalent (e.g., TiC, $$Mn4N,, $$, $$Fe3H,, $$, $$VH{0.56},, $$, $$TiH{1.7}$$).

  • They possess high melting points, are very hard, retain metallic conductivity, and are chemically inert.

Alloy Formation

  • Alloys are blends of metals with metallic radii within 15% of each other.

  • Transition metals readily form alloys due to their similar radii.

  • These alloys are typically hard and often have high melting points.

  • Examples include ferrous alloys (Cr, V, W, Mo, Mn), brass (Cu-Zn), and bronze (Cu-Sn).

Oxides and Oxoanions of Metals

  • Formed by the reaction of metals with oxygen at high temperatures.

  • All metals except Sc form MO oxides (ionic).

  • The highest oxidation number often coincides with the group number.

  • As the oxidation number increases, ionic character decreases.

  • Acidic character predominates in higher oxides (e.g., $$Mn2O7, CrO3, V2O_5$$).

Potassium Dichromate ($$K2Cr2O_7$$)

  • Prepared from chromite ore ($$FeCr2O4$$) by fusion with sodium or potassium carbonate in air.

  • The yellow solution of sodium chromate acidified with sulfuric acid yields orange sodium dichromate.

  • Sodium dichromate treated with potassium chloride yields potassium dichromate.

  • Chromates and dichromates are interconvertible based on pH.

  • It is a strong oxidizing agent in acidic solution:

$$Cr2O7^{2-} + 14H^+ + 6e^- \rightleftharpoons 2Cr^{3+} + 7H_2O( ($$ ($$E^o$$ = 1.33V)

  • It oxidizes iodides to iodine, sulfides to sulfur, tin(II) to tin(IV), and iron(II) salts to iron(III).

Potassium Permanganate (KMnO4KMnO_4$$KMnO_4$$)

  • Prepared by the fusion of $$MnO2withalkalimetalhydroxideandanoxidizingagentlike with alkali metal hydroxide and an oxidizing agent like $$ with alkali metal hydroxide and an oxidizing agent like $$KNO3$$.

  • The dark green $$K2MnO4$$ disproportionates in neutral or acidic solution to give permanganate.

$$MnO2 + 4KOH + O2 \rightarrow 2K2MnO4 + 2H2O $$ $$3MnO^{2-}4 + 4H^+ \rightarrow 2MnO^{-}4 + MnO2 + 2H_2O$$

  • Industrially prepared by alkaline oxidative fusion of MnO2MnO_2$$MnO_2$$ followed by electrolytic oxidation.

$$2Mn^{2+} + 5S2O^{2-}8 + 8H2O \rightarrow 2MnO^{-}4 + 10SO^{2-}_4 + 16H^+$$

  • Acidified permanganate oxidizes oxalates to carbon dioxide, iron(II) to iron(III), nitrites to nitrates, and iodides to free iodine.

The Lanthanoids

  • Consist of fourteen elements following lanthanum (La).

  • Lanthanum is typically included with the lanthanoids in discussions of their properties.

  • They largely resemble each other much more than the transition metals, primarily exhibiting one oxidation state.

  • Their chemistry is well-suited to testing the effects of small changes in nuclear charge and sizes.

Actinoids

The names, symbols, and some properties include:

Actinium (Ac), Thorium (Th), Protactinium (Pa), Uranium (U), Neptunium (Np), Plutonium (Pu), Americium (Am), Curium (Cm), Berkelium (Bk), Californium (Cf), Einsteinium (Es), Fermium (Fm), Mendelevium (Md), Nobelium (No), Lawrencium (Lr).

Electronic Configuration

  • Atoms have a 6s26s^2$$6s^2$$ configuration but variable occupancy of the 4f level.

  • Tripositive ions are represented as 4fn4f^n$$4f^n$$ (n = 1 to 14).

Atomic and Ionic Sizes

  • Overall decrease in atomic and ionic radii from lanthanum to lutetium (lanthanoid contraction).

  • Irregular decrease in atomic radii but regular in M3+M^{3+}$$M^{3+}$$ ions.

Oxidation States

  • Primarily exhibit La(II) and Ln(III) forms of compounds. However, +2 and +4 oxidation states can be achieved in solution or solid compounds.

  • CeIV is favored due to its noble gas configuration.

  • Pr, Nd, Tb, and Dy can exist in the +4 state, but primarily as oxides.

Lanthanoids react with hydrogen when heated in the gas phase and form carbides such as $$Ln3C,, $$, $$Ln2C3,and, and $$, and $$LnC2$$.

These compounds liberate hydrogen from dilute acids and burn in halogens to form halides. They also form $$M2O3oxidesand oxides and $$ oxides and $$M(OH)_3$$ hydroxides.

Other characteristics include:

Lanthanoids are mainly used in the production of alloy steels for plates and pipes

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The d- and f- Block Elements

d-Block Elements

  • Located in Groups 3-12 of the periodic table.

  • Characterized by the progressive filling of d orbitals, influencing their chemical properties.

  • Exhibit metallic properties such as high tensile strength, ductility, malleability, with good thermal and electrical conductivity.

  • Often form colored ions and display variable oxidation states due to the involvement of d electrons in chemical bonding.

  • Divided into four transition metal series: 3d (Sc to Zn), 4d (Y to Cd), 5d (La, Hf to Hg), and 6d (Ac, Rf to Cn).

f-Block Elements

  • Positioned in a separate panel at the bottom of the periodic table to maintain the periodic table's structure.

  • Distinguished by the progressive filling of 4f and 5f orbitals.

  • Comprise two inner transition metal series: lanthanoids (4f series, Ce to Lu) and actinoids (5f series, Th to Lr).

  • Many actinoids are radioactive, with significant roles in nuclear applications and research.

Transition Metals

  • Defined by IUPAC as elements having an incomplete d subshell in neutral atoms or their ions.

  • Term originally denoted elements with properties intermediate between s- and p-block elements.

  • Exhibit a wide range of chemical behaviors, including catalytic activity and the formation of complex ions.

  • Group 12 elements—zinc, cadmium, and mercury—possess a complete d10d^{10} configuration and are generally excluded from the transition metals category but are often studied alongside them due to similar chemical behaviors.

Inner Transition Metals

  • Consist of the lanthanoids (cerium to lutetium) and actinoids (thorium to lawrencium).

  • Actinoids, such as thorium, protactinium, and uranium, are vital as sources of nuclear energy.

  • Lanthanoids are used in various applications, including magnets, catalysts, and phosphors.

Electronic Configuration

  • Follow a general electronic configuration of (n1)d110ns12(n-1)d^{1-10} ns^{1-2}, with exceptions like palladium (Pd), which has a 4d105s04d^{10}5s^0 configuration.

  • Deviations from the general configuration arise due to minimal energy differences between (n1)d(n-1)d and nsns orbitals.

  • Stability of half-filled and completely filled d orbitals significantly influences electronic configurations.

  • Noteworthy examples:

    • Chromium (Cr): 3d54s13d^5 4s^1 instead of 3d44s23d^4 4s^2.

    • Copper (Cu): 3d104s13d^{10} 4s^1 instead of 3d94s23d^9 4s^2.

  • Zinc (Zn), cadmium (Cd), mercury (Hg), and copernicium (Cn) have a (n1)d10ns2(n-1)d^{10} ns^2 configuration and are not considered transition elements due to their completely filled d orbitals.

Properties of Transition Elements

  • Display a diverse array of oxidation states, facilitating their participation in numerous chemical reactions.

  • Commonly form colored ions as a result of electronic transitions within the d orbitals.

  • Exhibit a propensity for complex formation with ligands, leading to a variety of coordination compounds.

  • Act as effective catalysts in various industrial processes.

  • Demonstrate paramagnetic behavior due to unpaired electrons in their d orbitals.

  • Exhibit similarities within horizontal rows, reflecting gradual changes in electronic structure.

Physical Properties

  • Characterized by metallic attributes, including high tensile strength, ductility, malleability, and excellent thermal and electrical conductivity.

  • Exceptions include zinc, cadmium, mercury, and manganese, which deviate from typical metallic behavior to varying degrees.

  • Generally hard (excluding Zn, Cd, and Hg) with low volatility, making them suitable for structural applications.

  • Exhibit high melting and boiling points due to the involvement of (n1)d(n-1)d and nsns electrons in metallic bonding.

  • Melting points typically peak at d5d^5 (except for Mn and Tc) and decrease with increasing atomic number.

Enthalpy of Atomization

  • Exhibit high enthalpies of atomization, indicating strong metallic bonding.

  • Enthalpies generally peak in the middle of each transition series, corresponding to maximum unpaired d electrons.

  • Stronger bonding is associated with a greater number of valence electrons.

  • Metals with high enthalpies of atomization tend to be chemically noble.

  • Second and third series elements generally have greater enthalpies of atomization compared to first series elements, reflecting stronger metallic bonding.

Atomic and Ionic Sizes

  • Ions with the same charge exhibit a progressive decrease in radius with increasing atomic number due to ineffective d electron shielding, increasing electrostatic attraction.

  • Atomic radii decrease similarly across each series.

  • Increase from the 3d to 4d series, but the 5d series radii are similar to the 4d series because of the lanthanoid contraction.

Lanthanoid Contraction

  • Caused by the filling of 4f orbitals before the 5d orbitals, leading to a regular decrease in atomic radii.

  • Compensates for the expected increase in atomic size down the group.

  • Results in similar radii for 4d and 5d series elements such as zirconium (Zr) and hafnium (Hf).

  • Imperfect shielding of 4f electrons results in a regular decrease in size with increasing nuclear charge.

Density

  • Increases from titanium (Z = 22) to copper (Z = 29) due to the decrease in metallic radius and increase in atomic mass.

Ionization Enthalpies

  • Increase along each series as a result of increasing nuclear charge.

  • Successive enthalpies do not increase as steeply as non-transition elements due to d-electron shielding.

  • Variation is less pronounced compared to non-transition elements.

  • When d-block elements form ions, ns electrons are generally lost before (n1)d(n – 1) d electrons.

  • Second ionization enthalpy increases with effective nuclear charge.

  • Breaks in trend observed at Mn2+ and Fe3+ due to stable d5d^5 configurations.

Exchange Energy

  • Stabilizes energy states and is proportional to the number of pairs of parallel spins.

  • Loss of exchange energy increases stability, making ionization more difficult.

  • The lowest common oxidation state is +2.

Oxidation States

  • Transition elements exhibit a variety of oxidation states, allowing them to form numerous compounds.

  • Elements in the middle of the series (e.g., Mn) display the greatest number of oxidation states.

  • Fewer oxidation states are observed at the extreme ends of the series (Sc, Ti, Cu, Zn).

  • Maximum oxidation states up to Mn correspond to the sum of s and d electrons.

  • Variability in oxidation states arises from the incomplete filling of d orbitals.

  • Higher oxidation states are favored by heavier members in the d-block (e.g., Mo(VI) and W(VI) are more stable than Cr(VI)).

  • Low oxidation states are stabilized by ligands with π\pi-acceptor character (e.g., Ni(CO)4, Fe(CO)5).

Standard Electrode Potentials

  • Copper's unique behavior (positive EoE^o) prevents it from liberating H2H_2 from acids.

  • General trend towards less negative EoE^o values across the series is related to increasing ionization enthalpies.

  • Values for Mn, Ni, and Zn are more negative than expected.

  • Stability of the half-filled d5d^5 subshell in Mn2+ and the completely filled d10d^{10} configuration in Zn2+ influence EoE^o values.

  • EoE^o for Ni is related to the highest negative \Delta[hyd}H^o.

Stability of Higher Oxidation States

  • Highest oxidation numbers achieved in TiX4TiX4, VF5VF5, and CrF6CrF_6.

  • Fluorine stabilizes higher oxidation states due to its high lattice energy or bond enthalpy.

  • Oxygen stabilizes high oxidation states in oxides and oxocations (e.g., VO2+,VO2+,TiO2+VO_2^+, VO^{2+}, TiO^{2+}).

  • Oxygen’s ability to form multiple bonds contributes to its superiority.

Chemical Reactivity

  • Transition metals vary in chemical reactivity.

  • Most are electropositive and dissolve in mineral acids.

  • First series metals (except Cu) are more reactive.

  • Formation of divalent cations decreases across the series.

  • Mn3+Mn^{3+} and Co3+Co^{3+} are the strongest oxidizing agents.

  • Ti2+Ti^{2+}, V2+V^{2+}, and Cr2+Cr^{2+} are strong reducing agents.

Magnetic Properties

  • Diamagnetic substances are repelled, while paramagnetic substances are attracted to magnetic fields.

  • Ferromagnetism is an extreme form of paramagnetism.

  • Paramagnetism arises from unpaired electrons.

  • Magnetic moment (μ)=n(n+2)(\mu) = \sqrt{n(n+2)} where n is the number of unpaired electrons.

Formation of Colored Ions

  • Excitation of electrons from lower to higher energy d orbitals.

  • Energy of excitation corresponds to the frequency of light absorbed, typically in the visible region.

  • Color observed corresponds to the complementary color of light absorbed.

  • Frequency depends on the nature of the ligand, affecting the crystal field splitting.

Trends in the M3+/M2+ Standard Electrode Potentials

  • Low value for Sc reflects the stability of Sc3+Sc^{3+} (noble gas configuration).

  • High value for Zn due to electron removal from the stable d10d^{10} configuration of Zn2+Zn^{2+}.

  • High value for Mn shows the stability of Mn2+Mn^{2+} (d5d^5).

  • Low value for Fe shows the stability of Fe3+Fe^{3+} (d5d^5).

  • Low value for V is related to the stability of V2+V^{2+} (half-filled t2gt_{2g} level).

Formation of Complex Compounds

  • Metal ions bind anions or neutral molecules to form complex species.

  • Transition metals form a large number of complexes due to their smaller sizes, high ionic charges, and availability of d orbitals.

Catalytic Properties

  • Transition metals and their compounds exhibit catalytic activity.

  • This is due to their ability to adopt multiple oxidation states and form complexes.

  • Examples include V2O5V2O5 (Contact Process), finely divided iron (Haber’s Process), and nickel (Catalytic Hydrogenation).

  • Catalysis involves bond formation between reactant molecules and catalyst surface atoms, increasing reactant concentration, and weakening bonds, thereby lowering the activation energy.

Formation of Interstitial Compounds

  • Small atoms (H, C, N) trapped inside the crystal lattices of metals.

  • These compounds are non-stoichiometric, neither ionic nor covalent (e.g., TiC, Mn4NMn4N, Fe3HFe3H, VH0.56VH{0.56}, TiH1.7TiH{1.7}).

  • They possess high melting points, are very hard, retain metallic conductivity, and are chemically inert.

Alloy Formation

  • Alloys are blends of metals with metallic radii within 15% of each other.

  • Transition metals readily form alloys due to their similar radii.

  • These alloys are typically hard and often have high melting points.

  • Examples include ferrous alloys (Cr, V, W, Mo, Mn), brass (Cu-Zn), and bronze (Cu-Sn).

Oxides and Oxoanions of Metals

  • Formed by the reaction of metals with oxygen at high temperatures.

  • All metals except Sc form MO oxides (ionic).

  • The highest oxidation number often coincides with the group number.

  • As the oxidation number increases, ionic character decreases.

  • Acidic character predominates in higher oxides (e.g., Mn2O7,CrO3,V2O5Mn2O7, CrO3, V2O_5).

Potassium Dichromate (K2Cr2O7K2Cr2O_7)

  • Prepared from chromite ore (FeCr2O4FeCr2O4) by fusion with sodium or potassium carbonate in air.

  • The yellow solution of sodium chromate acidified with sulfuric acid yields orange sodium dichromate.

  • Sodium dichromate treated with potassium chloride yields potassium dichromate.

  • Chromates and dichromates are interconvertible based on pH.

  • It is a strong oxidizing agent in acidic solution:

Cr2O72+14H++6e2Cr3++7H2OCr2O7^{2-} + 14H^+ + 6e^- \rightleftharpoons 2Cr^{3+} + 7H_2O (EoE^o = 1.33V)

  • It oxidizes iodides to iodine, sulfides to sulfur, tin(II) to tin(IV), and iron(II) salts to iron(III).

Potassium Permanganate (KMnO4KMnO_4)

  • Prepared by the fusion of MnO2MnO2 with alkali metal hydroxide and an oxidizing agent like KNO3KNO3.

  • The dark green K2MnO4K2MnO4 disproportionates in neutral or acidic solution to give permanganate.

MnO2+4KOH+O22K2MnO4+2H2OMnO2 + 4KOH + O2 \rightarrow 2K2MnO4 + 2H2O 3MnO24+4H+2MnO4+MnO2+2H2O3MnO^{2-}4 + 4H^+ \rightarrow 2MnO^{-}4 + MnO2 + 2H_2O

  • Industrially prepared by alkaline oxidative fusion of MnO2MnO_2 followed by electrolytic oxidation.

2Mn2++5S2O28+8H2O2MnO4+10SO42+16H+2Mn^{2+} + 5S2O^{2-}8 + 8H2O \rightarrow 2MnO^{-}4 + 10SO^{2-}_4 + 16H^+

  • Acidified permanganate oxidizes oxalates to carbon dioxide, iron(II) to iron(III), nitrites to nitrates, and iodides to free iodine.

The Lanthanoids

  • Consist of fourteen elements following lanthanum (La).

  • Lanthanum is typically included with the lanthanoids in discussions of their properties.

  • They largely resemble each other much more than the transition metals, primarily exhibiting one oxidation state.

  • Their chemistry is well-suited to testing the effects of small changes in nuclear charge and sizes.

Actinoids

The names, symbols, and some properties include:

Actinium (Ac), Thorium (Th), Protactinium (Pa), Uranium (U), Neptunium (Np), Plutonium (Pu), Americium (Am), Curium (Cm), Berkelium (Bk), Californium (Cf), Einsteinium (Es), Fermium (Fm), Mendelevium (Md), Nobelium (No), Lawrencium (Lr).

Electronic Configuration

  • Atoms have a 6s26s^2 configuration but variable occupancy of the 4f level.

  • Tripositive ions are represented as 4fn4f^n (n = 1 to 14).

Atomic and Ionic Sizes

  • Overall decrease in atomic and ionic radii from lanthanum to lutetium (lanthanoid contraction).

  • Irregular decrease in atomic radii but regular in M3+M^{3+} ions.

Oxidation States

  • Primarily exhibit La(II) and Ln(III) forms of compounds. However, +2 and +4 oxidation states can be achieved in solution or solid compounds.

  • CeIV is favored due to its noble gas configuration.

  • Pr, Nd, Tb, and Dy can exist in the +4 state, but primarily as oxides.

Lanthanoids react with hydrogen when heated in the gas phase and form carbides such as Ln3CLn3C, Ln2C3Ln2C3, and LnC2LnC2.

These compounds liberate hydrogen from dilute acids and burn in halogens to form halides. They also form M2O3M2O3 oxides and M(OH)3M(OH)_3 hydroxides.

Other characteristics include:

Lanthanoids are mainly used in the production of alloy steels for plates and pipes