Superheavy elements have become a matter of concern in theoretical chemistry for their unusual trends on the periodic table. Element 113 and 114 which have not been synthesized yet have $7s^2$ $7p_{1/2}^1$ and $7s^2$ $7p_{1/2}^2$ valence configurations, respectively. Considerable changes of molecular structures, vibrations, and stabilities are expected from spin-orbit interactions for molecules containing these superheavy elements since the $p_{1/2}$ valence is stabilized by enormous 7p spin-orbit splitting. For MX, $MX_3$ (M=Tl, 113, X=H, F), $MX_2$, $MX_4$ (M=Pb, 114, X=H, F), we performed geometry optimizations and normal mode analysis at the HF level of theory, and evaluated the stabilities at the CCSD(T) level using relativistic effective core potential with and without spin-orbit interactions. Spin-orbit coupling contracts the bond lengths for all cases and the bond contraction is more significant for the hydrides than the fluorides. Normal mode analysis reveal that molecular shapes of 113 and 114 molecules are analogous to Tl and Pb ones except for $113H_3$ and $113F_3$, and changes for vibrational frequencies of the hydrides by spin-orbit interactions are substantial. The bond energies are reduced largely by spin-orbit interactions. The bonds become very weak and, in particular, element 114 seems to be chemically inert. The hydrides and fluorides of 113 and 114 prefer the low oxidation state. These results can be explained by the stabilization and the relativistic radial contractions of the $p_{1/2}$ valence spinor by spin-orbit splitting.
