If this model is correct, we should observe electride character in both the valence and conduction bands. Thus, we examined charge density at the top of the valence band and bottom of the conduction band in Sc2C and Al2C (Figures ). This indeed revealed electride character in both states, which could only result from hybridization of the electride electron and empty metal orbitals. This hybridization is analogous to a donor-acceptor interaction in molecules, such as BH3-NH3, but with the 2D electron layer playing the role of the donor and the 2D M2C atoms playing the role of acceptor. Therefore, as overlap increases between donor (electride electrons) and acceptor (empty metal-carbide orbitals), the valence and conduction bands split more, and the band gap increases. Presumably, the greatest hybridization seen in the Al2C system is facilitated by aluminum being most electronegative, since the empty Al orbitals are closer in energy to the electride electrons. This directly leads us to a powerful design rule for layered semiconducting electrides: that increasing metal electronegativity leads to increased electron-metal hybridization, yielding an increased band gap.