3d–series consists of elements from Sc (at no.21) to Zn (at no.30). These elements lie in the 4^th period of the periodic table. In the atoms of these elements the last electron goes to 3d–orbitals, i.e., in this series 3d orbitals are progressively filled up with electrons as we move from Sc to Zn.

It may be noted that the configurations of Cr₂₄ and Cu₂₉ (two elements)are anomalous, since Cr₂₄ has 5 electrons (instead of 4) in 3d orbitals and Cu₂₉ has 10 electrons (instead of 9 )in these orbitals. Thus the correct electronic configurations of Cr₂₄ and Cu₂₉ are [Ar] ₁₈3d⁵4s¹ [instead of [Ar]₁₈3d⁴4s² and [Ar]₁₈3d¹⁰4s¹ instead of [Ar]₁₈3d⁹4s² respectively.

Complete and valence shell electronic configurations of the atoms of 3d–series elements can be written as follows. Here [Ar]₁₈ = 2, 8, 8(Three shells).

Complete configuration = [Ar]₁₈ 3d¹⁻¹⁰ 4s¹⁻² ; 2, 8,(8 + [1−10]), 1 or 2 (four shells); which otherwise can be written as 2, 8, (9 to 18), 1 or 2; i.e., 2, 8, 3s²p⁶d^{1 − 10}, 4s^{1, 2}. Valence–shell configuration = 3d¹⁻¹⁰ 4s^{1, 2}

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