Research on 2D materials is one of the leading topics in the fields of condensed matter physics and materials science, due to their novel properties which are absent in their bulk allotropes. The 2D limitation provides great flexibility to engineer the electronic properties, which is crucial for innovative device applications. In this review, the recent research on the electronic properties of elemental 2D materials, which do not exist in nature, is focused. These 2D materials are stabilized by their underlying substrates, leading to the abundant buckled structures. The buckling can break symmetries, making it possible to explore new emerging physics, such as topological superconductivity, valley-polarized metals, and the quantum spin Hall effect in these 2D materials. The relationship between the degree of buckling and the electronic structures in these 2D materials is reviewed from both the experimental side and simulation results, and finally, the challenges and outlook for this field are discussed.