What are transition metals?

Short Answer

Transition metals are the elements found in the d-block (Groups 3 to 12) of the periodic table.

  • They have incomplete d-subshells in their atoms or ions, which gives them unique properties like variable oxidation states, formation of colored compounds, and catalytic behavior.
  • Examples include iron (Fe), copper (Cu), nickel (Ni), and chromium (Cr). They are good conductors, malleable, and strong metals.
Detailed Explanation :

Definition of Transition Metals

Transition metals are elements whose atoms or cations have an incomplete d-subshell. They occupy the central block (d-block) of the periodic table. Their general electronic configuration is (n-1)d¹⁻¹⁰ns¹⁻², depending on the element and its oxidation state.

  • The incomplete d-orbitals are responsible for many distinct chemical and physical properties.
  • Transition metals are located between Group 2 (alkaline earth metals) and Group 13 (post-transition metals).

Physical Properties

  1. High Melting and Boiling Points:
    • Strong metallic bonding due to delocalized d-electrons.
  2. High Density:
    • Atoms are tightly packed; heavier d-block elements are denser.
  3. Hard and Malleable:
    • Can be hammered or rolled into sheets without breaking.
  4. Metallic Luster:
    • Shiny appearance due to free-moving d-electrons reflecting light.
  5. Conductivity:
    • Good conductors of heat and electricity because of mobile valence electrons.

Chemical Properties

  1. Variable Oxidation States:
    • Transition metals can exhibit more than one oxidation state, usually differing by 1.
    • Example: Iron → Fe²⁺, Fe³⁺; Copper → Cu⁺, Cu²⁺.
  2. Formation of Colored Compounds:
    • Partially filled d-orbitals allow d-d electron transitions, producing colorful compounds.
    • Example: Cu²⁺ → blue solution in water; Cr³⁺ → green compounds.
  3. Formation of Complexes:
    • Can form coordination compounds with ligands (molecules or ions that donate electrons).
    • Example: [Fe(CN)₆]³⁻, [Cu(NH₃)₄]²⁺.
  4. Catalytic Properties:
    • Transition metals often speed up reactions without being consumed.
    • Examples: Fe in Haber process, V₂O₅ in contact process.
  5. Formation of Alloys:
    • Can be mixed with other metals to form strong alloys like steel (Fe + C) or brass (Cu + Zn).

Trends in Transition Metals

  1. Atomic and Ionic Size:
    • Atomic size decreases slightly across a period due to increasing nuclear charge.
    • Down a group, size increases due to added electron shells.
  2. Ionization Energy:
    • Higher than s-block elements; increases gradually across the d-block.
  3. Electronegativity:
    • Moderate values; varies with oxidation state.
  4. Density and Hardness:
    • Increase down a group due to heavier atoms and stronger metallic bonding.

Examples of Transition Metals

  • Iron (Fe): Used in steel, magnets, and catalysts.
  • Copper (Cu): Electrical wiring, plumbing, and colored compounds.
  • Chromium (Cr): Stainless steel and pigments.
  • Nickel (Ni): Batteries, stainless steel, coins.

Significance of Transition Metals

  1. Industrial Applications:
    • Catalysts in chemical reactions, alloys, and electronics.
  2. Biological Role:
    • Iron in hemoglobin, copper in enzymes, zinc in coenzymes.
  3. Chemical Research:
    • Complex formation and oxidation-reduction reactions are essential for inorganic chemistry studies.
  4. Color and Pigments:
    • Used in paints, glass, and dyes because of colored ions.
Conclusion

Transition metals are d-block elements with incomplete d-orbitals, giving them variable oxidation states, colored compounds, catalytic properties, and complex formation ability. They are strong, malleable, good conductors with significant industrial, biological, and chemical importance. Their unique properties make them central to chemistry, materials science, and various technologies.