Why are d orbitals sometimes used to form hybrid orbitals?...

Why are $d$ orbitals sometimes used to form hybrid orbitals? Which period of elements does not use $d$ orbitals for hybridization? If necessary, which $d$ orbitals $(3 d, 4 d, 5 d$, or $6 d)$ would sulfur use to form hybrid orbitals requiring $d$ atomic orbitals? Answer the same question for arsenic and for iodine.

Key Concepts

Selection of d Orbitals Based on Principal Quantum Number

When d orbitals participate in hybridization, they are chosen from the same principal quantum level as the atom’s valence electrons. For example, a period 3 element like sulfur would use 3d orbitals, a period 4 element like arsenic would use 4d orbitals, and a period 5 element like iodine would use 5d orbitals.

Period-Specific Orbital Availability

Elements in the second period do not have d orbitals in their valence shell because their highest occupied energy level is n = 2, which only contains s and p orbitals. Therefore, second-period elements (like carbon, nitrogen, and oxygen) cannot use d orbitals for hybridization.

Hybridization

Hybridization is the concept where atomic orbitals, such as s and p orbitals and sometimes d orbitals, mix to form new, equivalent orbitals that are better suited for bonding in molecules. This process helps explain molecular geometries and bond formation, especially in cases where the standard valence orbitals do not provide a sufficient number of bonding sites or the correct spatial arrangements.

Availability of d Orbitals

d orbitals start to become available for bonding in elements with a principal quantum number of 3 or greater. They are invoked in hybridization when an atom needs extra orbitals to form additional bonds or to account for expanded valence shells, as seen in hypervalent molecules.

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