In the development of 2D materials, the monolayers of group–IIA elements of the periodic table have played a minor role. Only a few groups are studying monolayers of these elements, which are of interest primarily owing to their metallic behavior and multivalencyMultivalency. Coordination to a larger number of nearest neighbors with a smoother electron distribution than for localized covalent bondingCovalent bonding is the main characteristic of these structures with metallic bondingMetallic bonding. However, due to the low cohesive energies of single-atomic layers, synthesisSynthesis is quite difficult in comparison with that of their bulk structures. The monolayers of the alkaline-earth metals Be, Mg, Ca, Sr, and Ba are referred to as berylleneBeryllene, magneseneMagnesene, calceneCalcene, stronteneStrontene, and bareneBarene, analogous to the nomenclature used for the other main group elements. The known 3D structures of these metals clearly prefer close-packed structures or 3D clusters of atoms rather than extended layered assemblies. This explains why systematic investigations of metallic monolayers for alkaline-earth elements but also other metals are still widely lacking. Since metallic bondingMetallic bonding allows atoms to be more mobile than in rigid directional covalent bonding, these 2D networks are of special interest for applications involving surface chemistry, such as catalysis and sensing.