D Block and F Block Elements Study Notes

D Block and F Block Elements

Overview of D Block Elements

  • Definition: D block elements are classified when the last electron enters the d subshell.
  • Series: There are four series of d block elements:
      - 3d Series: Scandium (Sc, atomic number 21), Titanium (Ti, 22), Vanadium (V, 23), Chromium (Cr, 24), Manganese (Mn, 25), Iron (Fe, 26), Cobalt (Co, 27), Nickel (Ni, 28), Copper (Cu, 29), Zinc (Zn, 30).
      - 4d Series: Begins with Yttrium (Y, 39) and ends with Cadmium (Cd, 48).
      - 5d Series: From Lanthanum (La, 57) to Hassium (Hs, 108).
      - 6d Series: Introduces elements from atomic number 103 to 118.
  • Important Elements:
      - The first man-made metal is Technetium (Tc).

Properties of D Block Elements

Melting Points
  • Highest Melting Point: Tungsten (W), belonging to the 5d series.
  • Lowest Melting Point: Mercury (Hg), also from the 5d series.
Densities
  • Highest Density: Iridium (Ir).
  • Lowest Density: Scandium (Sc). Density increases down the groups, and is ranked as:
      - 3d < 4d < 5d < 6d
  • Example densities: Iridium = 22.57 g/cm³, Scandium = 2.61 g/cm³.
Oxidation States
  • Highest Oxidation State: Ruthenium (Ru) and Osmium (Os), both with +8.
  • Common Oxidation States include:
      - Sc: +2, +3 (more stable +3)
      - Ti: +2, +3, +4 (more stable +4)
      - V: +2, +3, +4, +5 (more stable +5)
      - Cr: +2, +3, +4, +5, +6 (more stable +3, +6)
      - Mn: +2, +3, +4, +5, +6, +7 (more stable +2, +4, +7)
      - Fe: +2, +3, +4, +6 (more stable +2, +3)
Electronic Configuration
  • General Electronic Configuration: [n−1]d1−10ns1−2[n-1]d^{1-10}ns^{1-2}.
  • Remark: Transition elements are defined based on d subshell having partially filled orbitals.
  • Elements like Zn, Cd, and Hg are d block but not transition elements due to having full d subshells.

Physical Properties

Atomic Radius
  • Trend: Atomic radius increases across a period due to decreased shielding effect.
  • Exceptional Cases: Nickel (Ni) has the least atomic radius in the d block due to poor shielding and lanthanide contraction effects.
      - Lanthanide Contraction: Refers to the decrease in atomic and ionic size of the lanthanide elements with increasing atomic number, impacting the atomic sizes of adjacent d block elements.
Metallic Nature
  • Conductivity Order: Silver (Ag) > Copper (Cu) > Gold (Au) > Aluminum (Al) due to outermost s and d electrons.
Melting Points
  • Directly proportional to the number of unpaired electrons.
  • Example graph explains trends with notable increases and drops around specific elements like Chromium (Cr).
Density
  • General trend indicates density increases down a group, but exceptions occur (e.g., Zn < Cu).
Color in Compounds
  • Colored Compounds: Only those with unpaired d electrons exhibit color. D0 and D10 configurations are colorless.
  • Reason for Color: Color arises due to d-d transitions, where electrons absorb certain wavelengths to promote to higher energy states.
  • Complementary Colors: E.g., red compound appears green, violet appears yellow, etc.
Magnetic Properties
  • Diamagnetic vs. Paramagnetic:
      - Diamagnetic: No unpaired electrons.
      - Paramagnetic: Unpaired electrons present.
  • Formula for Spin Magnetic Moment: extμs=extsqrt(n(n+2))ext{μ}_s = ext{sqrt}(n(n + 2)) where n is the number of unpaired electrons.
Alloy Formation
  • Definition: Homogeneous mixtures of two or more metals or nonmetals.
  • Examples of Alloys:
      - Brass: Copper (Cu) + Zinc (Zn)
      - Bronze: Copper (Cu) + Tin (Sn)
      - German Silver: Copper (Cu) + Zinc (Zn) + Nickel (Ni)
  • Merge with Mercury: Compounds with mercury are called amalgams.
      - Iron (Fe), Cobalt (Co), and Nickel (Ni) do not form amalgams with mercury due to size discrepancies.
Catalytic Properties
  • Why D Block Elements as Catalysts: They display variable oxidation states and have unpaired electrons allowing free valencies to facilitate chemical reactions.
  • Examples:
      - Haber's Catalyst: Iron (Fe) with Molybdenum (Mo) as a promoter in the synthesis of ammonia (NH3).

Enthalpy of Atomization

  • Definition: Energy required to separate one mole of substance into gaseous atoms.
  • Relation to D Block Elements: Higher unpaired electrons equal greater enthalpy of atomization, thus higher energy needed to break bonds.
  • Notable Points:
      - Manganese (Mn) has lower enthalpy than transition metals because of its stable half-filled d orbital.

Chromate and Dichromate Systems

  • Chemical Equilibrium:
      - Chromate extCrO42−ext{CrO}_4^{2-}
  • Preparation of Potassium Dichromate (K2Cr2O7):
      1. Chromite to Chromate: Heating chromite with sodium carbonate (Na2CO3) or sodium hydroxide (NaOH) and oxygen forms sodium chromate (Na2CrO4Na_2CrO_4).
      2. Formation of Dichromate: Sodium chromate treated with sulfuric acid (H2SO4) equals potassium dichromate.
  • Important Reactions:
      - 4FeCr2O4+8Na2CO3+7O2<br/>ightarrow2Fe2O3+8Na2CrO4+8CO24FeCr_2O_4 + 8Na_2CO_3 + 7O_2 <br /> ightarrow 2Fe_2O_3 + 8Na_2CrO_4 + 8CO_2
      - Dichromate to Chromate Equilibrium:
        - Basic Medium: Cr2O72−+2OH−<br/>ightarrow2CrO42−+H2OCr_2O_7^{2-} + 2OH^- <br /> ightarrow 2CrO_4^{2-} + H_2O
        - Acidic Medium: 2CrO42−+2H+<br/>ightarrowCr2O72−+H2O2CrO_4^{2-} + 2H^+ <br /> ightarrow Cr_2O_7^{2-} + H_2O

Conclusion

  • Transition elements play a crucial role in numerous chemical processes, being defined not only by their position in the periodic table but also by their unique physical and chemical properties. Understanding their properties such as melting point, density, oxidation states, color, and their behavior as catalysts is foundational for studies in inorganic chemistry.