MP2/aug-cc-pVTZ calculations were carried out on complexes of ZH₄, ZFH₃ and ZF₄ (Z = C, Si and Ge) molecules with HCN, LiCN and Cl⁻ species acting as Lewis bases through nitrogen centre or chlorine ion. Z-Atoms in these complexes usually act as Lewis acid centres forming σ-hole bonds with Lewis bases. Such noncovalent interactions may adopt a name of tetrel bonds since they concern the elements of the group IV. There are exceptions for complexes of CH₄ and CF₄, as well as for the F₄Si⋯NCH complex where the tetrel bond is not formed. The energetic and geometrical parameters of the complexes were analyzed and numerous correlations between them were found. The Quantum Theory of ‘Atoms in Molecules’ and Natural Bonds Orbital (NBO) method used here should deepen the understanding of the nature of the tetrel bond. An analysis of the electrostatic potential surfaces of the interacting species is performed. The electron charge redistribution, being the result of the tetrel bond formation, is the same as that of the S_N2 reaction. The energetic and geometrical parameters of the complexes analyzed here correspond to different stages of the S_N2 process.