This study demonstrates that the properties of graphene can be controlled through reversible hydrogenation. By exposing graphene to atomic hydrogen, it is possible to transform the highly conductive semimetal into an insulator. Transmission electron microscopy reveals that the hexagonal lattice of graphene is preserved but its period becomes significantly shorter, indicating a new graphene-based derivative. The hydrogenation process is reversible, as the original metallic state and lattice spacing can be restored by annealing, and the quantum Hall effect recovers. The work confirms the concept of chemical modification of graphene, which opens up a range of new two-dimensional crystals with tailored electronic and other properties. Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, is known for its exceptional electronic properties and atomic thickness. The chemical modification of graphene remains underexplored, but the ability of carbon to change its coordination and bonding can be used to create chemical derivatives of graphene. This could expand the range of electronic, chemical, mechanical, and other properties achievable in graphene-based materials, making them more suitable for specific applications. The idea of attaching atomic hydrogen to each site of the graphene lattice changes the hybridization from sp² to sp³, removing the conducting π-bands and opening an energy gap. Previous studies on hydrogen absorption on graphitic surfaces were mainly focused on hydrogen storage, with research on physisorbed molecular hydrogen. More recently, atomic hydrogen chemisorbed on carbon nanotubes has been studied theoretically and experimentally. In this work, reversible hydrogenation of single-layer graphene is reported, resulting in dramatic changes in its properties as observed by transport measurements, Raman spectroscopy, and transmission electron microscopy. Graphene crystals were prepared by micromechanical cleavage of graphite on an oxidized silicon substrate and identified by optical contrast and Raman signatures. Three types of samples were used: large crystals for Raman studies, standard Hall bar devices, and free-standing membranes for TEM. The samples were first annealed at 300°C in argon atmosphere to remove contamination. After characterization, the samples were exposed to cold hydrogen plasma. The hydrogenation process resulted in significant changes in the electronic properties of graphene, including the transition from a metallic to an insulating state. The quantum Hall effect disappeared, and the resistivity increased with decreasing temperature. The mobility decreased, and the temperature dependence of resistivity was fitted by the function exp[(T₀/T)^(1/3)], indicating variable-range hopping in two dimensions. The hydrogenated devices were stable at room temperature for many weeks, showing the same characteristics during repeated measurements. However, the original metallic state could be restored by annealing. After annealing, the devices returned to their original state, with resistivity as a function of gate voltage reaching a maximum value and becoming weakly temperature dependent. The mobility recovered, and the quantum Hall effect reappeared. However, the recovery was not complete, as graphene remained p-doped, and the quantum Hall effect didThis study demonstrates that the properties of graphene can be controlled through reversible hydrogenation. By exposing graphene to atomic hydrogen, it is possible to transform the highly conductive semimetal into an insulator. Transmission electron microscopy reveals that the hexagonal lattice of graphene is preserved but its period becomes significantly shorter, indicating a new graphene-based derivative. The hydrogenation process is reversible, as the original metallic state and lattice spacing can be restored by annealing, and the quantum Hall effect recovers. The work confirms the concept of chemical modification of graphene, which opens up a range of new two-dimensional crystals with tailored electronic and other properties. Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, is known for its exceptional electronic properties and atomic thickness. The chemical modification of graphene remains underexplored, but the ability of carbon to change its coordination and bonding can be used to create chemical derivatives of graphene. This could expand the range of electronic, chemical, mechanical, and other properties achievable in graphene-based materials, making them more suitable for specific applications. The idea of attaching atomic hydrogen to each site of the graphene lattice changes the hybridization from sp² to sp³, removing the conducting π-bands and opening an energy gap. Previous studies on hydrogen absorption on graphitic surfaces were mainly focused on hydrogen storage, with research on physisorbed molecular hydrogen. More recently, atomic hydrogen chemisorbed on carbon nanotubes has been studied theoretically and experimentally. In this work, reversible hydrogenation of single-layer graphene is reported, resulting in dramatic changes in its properties as observed by transport measurements, Raman spectroscopy, and transmission electron microscopy. Graphene crystals were prepared by micromechanical cleavage of graphite on an oxidized silicon substrate and identified by optical contrast and Raman signatures. Three types of samples were used: large crystals for Raman studies, standard Hall bar devices, and free-standing membranes for TEM. The samples were first annealed at 300°C in argon atmosphere to remove contamination. After characterization, the samples were exposed to cold hydrogen plasma. The hydrogenation process resulted in significant changes in the electronic properties of graphene, including the transition from a metallic to an insulating state. The quantum Hall effect disappeared, and the resistivity increased with decreasing temperature. The mobility decreased, and the temperature dependence of resistivity was fitted by the function exp[(T₀/T)^(1/3)], indicating variable-range hopping in two dimensions. The hydrogenated devices were stable at room temperature for many weeks, showing the same characteristics during repeated measurements. However, the original metallic state could be restored by annealing. After annealing, the devices returned to their original state, with resistivity as a function of gate voltage reaching a maximum value and becoming weakly temperature dependent. The mobility recovered, and the quantum Hall effect reappeared. However, the recovery was not complete, as graphene remained p-doped, and the quantum Hall effect did