Forces also covalent

The electrodynamic forces proposed for stabilizing jellium provide the principal type of bonding in molecular crystals such as solid methane, rare gas crystals, solid anthracene, and the like. These forces also form the inter-chain bonding of long-chain molecules in polymeric materials (the intra-molecular bonding within the chains is usually covalent). 

The adhesion of a coating to plastic is related to the substrate wettability and also to physical-chemical forces. Both covalent (bond formation) and dispersive (London or van der Waals) forces are responsible for the adhesion of the coating due to physical-chemical forces. 

As the understanding of chemical bonding was advanced through such concepts as covalent and ionic bond, lone electron pairs etc., the theory of intermolecular forces also attempted to break down the interaction energy into a few simple and physically sensible concepts. To describe the nonrelativistic intermolecular interactions it is sufficient to express them in terms of the aforementioned four fundamental components electrostatic, induction, dispersion and exchange energies. 

Within the molecular sheets the interbond angles are almost exactly 90°, suggesting that simple pz orbitals are involved in the covalent bonding. The forces between the sheets are primarily van der Waals bonds, but, as in the selenium structure, there is no doubt that these forces also have an appreciable component of metallic character which increases with increasing atomic number, as is shown by the progressive... 

See also Covalent Bonds vs Non-Covalent Forces, DNA, Secondary Structure (from Chapter 2), Dynamics of Protein Folding... 

Many types of forces and interactions play a role in holding a protein together in its correct, native conformation. Some of these forces are covalent, but many are not. The primary structure of a protein—the order of amino acids in the polypeptide chain—depends on the formation of peptide bonds, which are covalent. Higher-order levels of structure, such as the conformation of the backbone (secondary structure) and the positions of all the atoms in the protein (tertiary structure), depend on noncovalent interactions. If the protein consists of several subunits, the interaction of the subunits (quaternary structure. Section 4.5) also depends on noncovalent interactions. Noncovalent stabilizing forces contribute to the most stable structure for a given protein, the one with the lowest energy. 

The range over which these forces are significant varies widely. Covalent bonds act over a few nanometres only. Interactions that are essentially electrostatic in nature, as in ionic bonds, operate over larger distances, and are proportional to 1/r, where r is the interionic distance. Ion-dipole interactions decrease more rapidly, being proportional to 1/r. Dipole-dipole interactions vary as Hp for static dipoles and as 1/r for rotating dipoles. Dispersion forces also decrease as 1/r. ... 

The properties of resins, which are the weakest components in every composite, will be considered first. For epoxy resin, the effect of crosslinking as a correlation of chemical structure with physical data was studied. Many properties can be understood by the molecular anisotropy of binding forces. Strong covalent and weak van der Waals forces act along and transverse to the polymer chains, respectively. This molecular anisotropy also exists in fiber materials, such as Kevlar, which consists of strong, highly stretched polymer chains, which are weakly bonded together. 

Electrostatic forces also result from slight displacement of electrons and nuclei in covalent molecules from proximity to electrostatic fields associated with the dipoles from other molecules. These are induced dipoles. The displacements cause interactions between the induced dipoles and the permanent dipoles creating forces of attraction. The energy of the induction forces, however, is small and not temperature-dependent. 

One of the greatest puzzles in natural sciences before the paper of Heitler and London (HL) was published in 1927 was the nature of the strong attractive interactions between neutral atoms which lead to the formation of a covalent chemical bond. It was clear that only electrostatic forces could be responsible for the interatomic attraction, but the application of classical laws of electrostatic interactions gave bond energies which were much too low. The explanation of a chemical bond in terms of classical electrostatic forces also violated the law of Earnshaw, which states that a static system held together by charge attractions should not be stable. 

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