Exchanging oxygen in the functional group C=O (i.e., carbonyl) for the less electronegative Group 16 elements sulfur or selenium, unexpectedly enhances the electronegativity of the C=X group in π‐conjugated molecules and reduces the molecular π HOMO–LUMO energy gap. Quantum‐chemical analyses revealed that the steric size of the chalcogen atom X is at the origin of this seemingly counterintuitive behavior. This tuning of the chemical properties of carbonyl compounds by varying the chalcogen atom size in the C=X bond can be applied in many fields of chemistry. This concept article delineates several useful applications in the fields of organocatalysis, supramolecular chemistry, and photo(electro)chemistry.