Skip to main content

Variable oxidation states; industrial uses of 3d elements

Short answer

Variable oxidation states occur because 3d and 4s electrons have similar energies, allowing both to participate in bonding with gradually increasing ionisation energies. Key industrial uses: Fe in steel and Haber catalyst, V2O5 for H2SO4, Ni in hydrogenation, Cr in stainless steel, Cu in wiring, Ti in aircraft alloys, Mn in dry cells, Co in magnets, Zn for galvanizing.

Why do transition elements show variable oxidation state? Point out the industrial applications of 3d-series elements.

Variable oxidation states

Transition elements show variable oxidation states because the (n−1)d and ns electrons have very nearly the same energy, so both the ns electrons and a variable number of (n−1)d electrons can take part in bonding. Successive ionisation energies rise gradually (unlike the sudden jump after the s-electrons in s-block metals), so ions of several charges can form. In the 3d series the states usually differ by one unit (e.g. Fe²⁺, Fe³⁺), unlike p-block elements whose states differ by two (Sn²⁺, Sn⁴⁺).

ElementScTiVCrMnFeCoNiCuZn
Common oxidation states+3+2, +3, +4+2, +3, +4, +5+2, +3, +6+2, +3, +4, +6, +7+2, +3+2, +3+2+1, +2+2
  • Sc has one stable state (+3, loses 3 electrons to reach argon core) and Zn only +2 (3d¹⁰ stable), so they show little variability.
  • The maximum state increases from Sc (+3) to Mn (+7), equal to the number of 3d + 4s electrons, then decreases after Mn because electrons are paired and the d orbitals become more stable.
  • Examples: MnO₄⁻ (+7), Cr₂O₇²⁻ (+6), VO₂⁺ (+5).

Industrial applications of 3d-series elements

  • Iron (steel, cast iron) in construction and machines; Fe as catalyst in Haber's process.
  • V₂O₅ as catalyst in contact process for H₂SO₄; vanadium steel for tools.
  • Ni as hydrogenation catalyst; Ni–Cd batteries; nichrome heating wire.
  • Cr: chrome plating, stainless steel; K₂Cr₂O₇ in tanning and as an oxidant.
  • Cu in electrical wires and PCB tracks (high conductivity); brass and bronze alloys.
  • Ti: light strong alloys for aircraft; TiO₂ as white pigment.
  • Mn: MnO₂ in dry cells and as catalyst; ferromanganese steel; KMnO₄ as oxidant.
  • Co: magnets (Alnico), Li-ion battery cathodes (LiCoO₂); Zn: galvanising iron and dry cell anodes.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Engineering Chemistry chapter 5 questions →