Interatomic and intermolecular bonds that are relatively weak and for which bonding energies are relatively small. Normally atomic or molecular dipoles are involved. Secondary bonding types are van der Waals and hydrogen.
? Secondary = van der Waals = physical (as opposite to chemical bonding that involves e- transfer)
? No e- transferred or shared Interaction of atomic/molecular dipoles
? Weak (< 100 KJ/mol or < 1 eV/atom)
? Exists:
1- Between virtually all atoms or molecules.
2- Evidenced for the inert gases, which have stable electron structures.
3- Between molecules in molecular structures that are covalently bonded.
? Secondary bonding forces arise from atomic or molecular dipoles (there is some separation of positive and negative portions of an atom or molecule).
? Hydrogen bonding, a special type of secondary bonding,
? These bonding mechanisms are:
1- Fluctuating Induced Dipole: (inert gases, H2, Cl2…)
A dipole may be created or induced in an atom or molecule that is normally electrically symmetric.
All atoms are experiencing constant vibrational motion that can cause instantaneous and short-lived distortions of this electrical symmetry, and the creation of small electric dipoles,
One of these dipoles can induce an adjacent and near adjacent molecule or atom, to become a dipole that is then weakly attracted or bonded to the first; this is one type of van der Waals bonding: forces are temporary and fluctuate with time.
The liquefaction and, in some cases, the solidification of the inert gases and other electrically neutral and symmetric molecules such as H2 and Cl2 are realized because of this type of bonding. Melting and boiling temperatures are extremely low in materials for which induced dipole bonding predominates