Theoretical predictions for α -decay properties of 283-339 Og using a shell-effect induced generalized liquid-drop model

. The α -decay half-lives of synthesized superheavy nuclei (SHN) from seaborgium to oganesson are calculated by employing the generalized liquid-drop model (GLDM), the Royer formula and the universal decay law (UDL) with experimental α -decay energies Q_α . For the GLDM, we consider the shell correction. The agreement between the experimental data and the calculations indicates that all the methods we used are successful to reproduce α -decay half-lives of known SHN. The decay-modes of known nuclei on the 294 Og decay-chain are also consistent with the experiments. For the unknown nuclei, the α -decay half-lives have been predicted by inputting Q_α values extracted from the newest Weizsäcker-Skyrme-4 (WS4) model. In the GLDM with shell correction, we adopt the constant α -preformation factor P_α as well as P_α extracted by Cluster Formation Model (CFM). To calculate CFM P_α values, we use FRDM binding energies and WS4 mass excess values. The relationship of P_α and Q_α shows that 294, 296, 314, 316, 320 Og isotopes are relatively stable. The competition between α -decay and spontaneous fission is discussed in detail for 283-339 Og isotopes. The decay-chains of 290-300 Og have also been presented. Since the α -decay half-lives of 283-303 Og isotopes are obviously lower than their spontaneous fission half-lives by more than 6 orders, these isotopes would mainly have α -decay. The 306-334 Og isotopes may undergo spontaneous fission. The nuclei 304, 305 Og would have both α -decay and spontaneous fission. By the shell-effect included GLDM with CFM P_α , we predict 295 Og undergoes α -decay and T_α^1/2 = 0.37 ms. The 296 Og is also α -decay and has T_α^1/2 = 0.40 ms.