(calculated for all electrons) with an established valence-based scale of electronegativity. This approach for evaluating 𝜒̅ 7 89: has proven useful both for analyzing chemical bonding and as a potent predictor of pKa. To better understand the chemical information provided by in situ electronegativity, we look in Table at how this quantity changes when comparing atoms inside crystals with those same atoms in isolation. For the case of urea, we additionally compare in situ electronegativity of atoms inside crystals and in isolated molecules. The formation of a potassium crystal from isolated atoms is characterized by an increase in in situ electronegativity, i.e., Δ𝜒̅ - 89: > 0. We remind that a positive Δ𝜒̅ 7 89: for a transformation means that electrons in basin A are on average stabilized. The stabilization, or increase in electronegativity, upon forming solid K from atoms is relatively small, only 1.1 eV×e -1 . In comparison, the formation of H2 from isolated atoms corresponds to an Δ𝜒̅ of 1.828 eV×e -1 . The absolute value of 𝜒̅ 7 89: is comparatively small in both the atom and the solid and is correctly, and as expected, indicating that the valence electrons in this material are weakly bound. This first example is important because it highlights that electronegativity reflect aspects of the electronic structure even in the absence of net charge transfer between atoms. In the crystallization of potassium, the number of electrons per atom, i.e., the atomic charge, does not change, yet the electronegativity does. The enhanced electronegativity is the result of a small orbital stabilization brought about by chemical bonding in the material.