For calcium, the electron configuration is $\mathrm{1s^2\:2s^2\:2p^6\:3s^2\:3p^6\:4s^2}$. Does it mean there's no electron in d sub-shell? Also, how would one write the electron configuration for a calcium ion?

  • 7
    $\begingroup$ What you provided is the ground-state configuration for calcium. In theory every atom "has" d-electrons, just not in the ground state. When excited (which is usually VERY rare), electrons can bump up to higher energy levels like p,d,f,etc. $\endgroup$
    – khaverim
    Mar 5, 2016 at 3:47
  • $\begingroup$ Because there is a possibility for electrons to transition to an excited state at all temperatures, other than absolute zero, there are some d-electrons present in $\ce{Ca}$ as well. $\endgroup$
    – ananta
    Jun 6, 2023 at 0:55

1 Answer 1


An isolated calcium atom has no $d$ electrons, but calcium in at least one compound has been found to incorporate $3d$ orbitals into its bonding. Krieck et al.[1],[2] describe the inverse sandwich complex $\ce{[(thf)3Ca(μ-C6H3}\text{-}\ce{1,3,5}\text{-}\ce{Ph3)Ca(thf)3]}$, a dicalcium complex in which what are ordinarily antibonding orbitals in the organic ligand overlap appropriately symmetric calcium $3d$ orbitals to become bonding between calcium and carbon. Note especially the oxidation state of calcium, $+1$. Calcium(II) would more likely show the classical predominantly ionic bonding in which the metal valence electrons play no role except the $4s$ electrons being largely transferred to the nonmetal atoms.


  1. Sven Krieck, Helmar Görls, Lian Yu, Markus Reiher, and Matthias Westerhausen (2009). "Stable “Inverse” Sandwich Complex with Unprecedented Organocalcium(I): Crystal Structures of [(thf)2Mg(Br)-C6H2-2,4,6-Ph3] and [(thf)3Ca{μ-C6H3-1,3,5-Ph3}Ca(thf)3]". J. Am. Chem. Soc. 131, 8, 2977–2985. https://doi.org/10.1021/ja808524y.

  2. Krieck, Sven; Görls, Helmar; Westerhausen, Matthias (2010). "Mechanistic Elucidation of the Formation of the Inverse Ca(I) Sandwich Complex [(thf)3Ca(μ-C6H3-1,3,5-Ph3)Ca(thf)3] and Stability of Aryl-Substituted Phenylcalcium Complexes". Journal of the American Chemical Society. 132 (35): 12492–12501. https://doi.org/10.1021/ja105534w. PMID 20718434.


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