The question of electronegativity is essential because two experimentally observed electrides-Y2C and Hf2S-are "hybrid" electrides , where the electride electron has some overlap with the adjacent metal orbitals, and electronegativity of the metal may be correlated with the degree of hybridization. This covalency plays an important role in defining the electronic structure of the electride because the electride electron is normally found around the Fermi level. Thus, as hybridization occurs, tunable band structures become possible, and indeed, Y2C is a semi-metal. This is unique among the layered electrides and raises the question of whether greater degrees of hybridization between metal and electride electron could lead to new categories of electride materials . These questions motivate our exploration of the M2C system, and especially of layered Sc2C.