Non-covalent interactions
A hydrogen bond (H-bond), is a specific type of interaction that involves dipole-dipole attraction between a partially positive hydrogen atom and a highly electronegative, partially negative oxygen, nitrogen, sulfur, or fluorine atom (not covalently bound to said hydrogen atom). It is not a covalent bond, but instead is classified as a strong non-covalent interaction. It is responsible for why water is a liquid at room temperature and not a gas (given water's low molecular weight). Most commonly, the strength of hydrogen bonds lies between 0 - 4 kcal/mol, but can sometimes be as strong as 40 kcal/mol In solvents such as chloroform or carbontetrachloride one observes e.g. for the interaction between amides additive values of about 5 kJ/mol. According to L. Pauling the strength of a hydrogen bond is essentially determined by the electrostatic charges. Measurements of thousands complexes in chloroform or carbontetrachloride have led to additive free energy increments for all kind of donor-acceptor combinations.
Chalcogen bond
A chalcogen bond is an attractive interaction in the family of σ-hole interactions, along with hydrogen bonds and halogen bonds. This family of attractive interactions has been modeled as an electron donor interacting with the σ* orbital of a C-X bond (X= hydrogen, halogen, chalcogen, pnictogen, etc.). Electron density mapping is often invoked to visualize the electron density of the donor and an electrophilic region on the acceptor, referred to as a σ-hole. Chalcogen bonds, much like hydrogen and halogen bonds, have been invoked in various non-covalent interactions, such as protein folding, crystal engineering, self-assembly, catalysis, transport, sensing, templation, and drug design.