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Why 3d elements are transition; valency characteristics

Short answer

3d elements are called transition elements because they lie between s- and p-blocks of the periodic table and have an incomplete 3d subshell. They show variable valency as 4s and 3d electrons have similar energies, both take part in bonding; states differ by one unit, common +2, and highest oxidation number equals sum of 4s and 3d electrons up to Mn +7.

Why are 3d-series elements called transition elements? Give their characteristic on the basis of valency.

Why 3d elements are called transition elements

The elements Sc to Zn lie between the s-block and p-block elements of the periodic table, and their properties change gradually from the strongly electropositive s-block metals to the less electropositive p-block elements. They have an incomplete 3d subshell, with electrons added to the inner (n−1)d orbitals, so they form a transition between the two blocks.

Characteristics based on valency (oxidation state)

  • They show variable valency because 4s and 3d electrons have nearly equal energies and both take part in bonding.
  • Common states: +2 (loss of both 4s electrons) for almost all; +3 for Sc, Ti, Cr, Fe, Co; Mn shows +2 to +7; Cu shows +1 and +2.
  • Successive states differ by one unit (Fe²⁺, Fe³⁺), not by two.
  • The highest oxidation state equals the sum of 4s and 3d electrons up to Mn (+7). Higher states are oxidising (MnO₄⁻, Cr₂O₇²⁻); lower states are reducing (Fe²⁺).
  • Zn shows only +2 and Sc only +3.

✓ Answer checked by Claude Opus 5.5 (high effort)

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