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Properties of Transition Metals | chemca

Properties of Transition Metals | chemca
Inorganic Chemistry

Properties of Transition Metals

Magnetic behavior, Color, Complexation, and Catalysis.

By chemca Team • Updated Jan 2026

The presence of unpaired electrons in the $(n-1)d$ orbitals gives transition metals unique properties such as magnetism and color. Their ability to exhibit variable oxidation states makes them excellent catalysts and complexing agents.

1. Magnetic Properties

Paramagnetism

Most transition metals are Paramagnetic (attracted by magnetic fields) due to the presence of unpaired electrons. Substances with no unpaired electrons are Diamagnetic (repelled).

Spin-Only Magnetic Moment Formula ($\mu$):
$$ \mu = \sqrt{n(n+2)} \text{ B.M.} $$

Where $n$ = Number of unpaired electrons, B.M. = Bohr Magneton.

Example Calculation:

$Mn^{2+}$ ($3d^5$): $n=5$ unpaired electrons.

$\mu = \sqrt{5(5+2)} = \sqrt{35} \approx 5.92$ B.M.

$Sc^{3+}$ ($3d^0$): $n=0$. $\mu = 0$ (Diamagnetic).

2. Formation of Coloured Ions

d-d Transitions

Most transition metal compounds are coloured in solid state or solution. This is due to the presence of an incomplete d-subshell ($d^1$ to $d^9$).

Mechanism:
  1. In a free ion, all 5 d-orbitals are degenerate (same energy).
  2. When ligands approach (in a complex/crystal), the d-orbitals split into two sets of different energies ($t_{2g}$ and $e_g$). This is Crystal Field Splitting.
  3. Electrons absorb energy from white light to jump from lower to higher d-orbitals (d-d transition).
  4. The transmitted light shows the Complementary Color of the absorbed light.
Colorless Ions: Ions with $d^0$ (e.g., $Sc^{3+}, Ti^{4+}$) or $d^{10}$ (e.g., $Zn^{2+}, Cu^+$) configurations are colorless because d-d transitions are not possible.
Example: Hydrated $Cu^{2+}$ ($3d^9$) absorbs red light and appears Blue.

3. Formation of Complex Compounds

Coordination Chemistry

Transition metals form a large number of complex compounds where the metal ion binds with anions or neutral molecules (Ligands).

Reasons for Complex Formation:
  • Small size of the metal ions.
  • High nuclear charge (high charge density).
  • Availability of vacant d-orbitals of suitable energy to accept lone pairs from ligands.
Examples:
$$ [Fe(CN)_6]^{3-}, \quad [Cu(NH_3)_4]^{2+}, \quad [Ni(CO)_4] $$

4. Catalytic Properties

Why are they good Catalysts?

Transition metals and their compounds are effective catalysts in many industrial processes.

Key Reasons:
  • Variable Oxidation States: Allows them to form unstable intermediates and provide a new reaction path with lower activation energy. Example: $V_2O_5$ in Contact Process oxidizes $SO_2$ to $SO_3$ by changing V form +5 to +4 and back.
  • Large Surface Area: Provides a surface for reactants to adsorb, increasing concentration and effective collisions. Example: Finely divided Fe in Haber's Process.
Common Catalysts:
  • Vanadium Pentoxide ($V_2O_5$): Contact Process ($H_2SO_4$ manufacture).
  • Finely divided Iron (Fe): Haber's Process ($NH_3$ manufacture).
  • Nickel (Ni): Hydrogenation of oils (Fats manufacture).
  • Titanium Chloride ($TiCl_4$): Ziegler-Natta Catalyst (Polymerization).

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