Electrostatic and ionic bonding

Although the Berzelius ionic theory achieved successes in interpreting inorganic compounds, it met persistent difficulties in the emerging domain of organic chemistry. By about 1860, E. Frankland, F. A. Kekule, and others had developed the opposing concept of valence (and specifically, the quadrivalence of carbon) to 

The ionic or electrostatic picture of bonding has an engaging simplicity. According to classical electrostatics, the energy of interaction (Ees) of particles with charges 0 and Qi at separation R is 

For a system consisting of four ions, with gi = — Qi = Qi = — Qa = e, the electrostatic energy is simply a sum of six such Coulombic terms, one for each distinct pair of ions  

Let us compare the energy of linear (Tim) and square (Tsq) arrangements, assuming the same nearest-neighbor distance R for each  

for any fixed R classical electrostatics favors a square over a linear arrangement by 10.8%, but the only true minimum is — 0. 

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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. 

The type of attractive forces within solids depends on the identity of the unit particle and the chemical bonds it can form. The forces between atoms in a covalent network solid (such as carbon in diamond) are covalent bonds. These bonds result when at least one pair of electrons is shared by two atoms. The forces between atoms within metallic elements (such as iron) are metallic bonds. Electrostatic attractions—also called ionic bonds—are the forces between ions, atoms which have lost one or more electrons to become positively charged ions or which have gained one or more electrons to become negatively charged ions (such as those found in NaCI). Ionic compounds are often known as salts. Covalent, metallic, and ionic bonds are strong chemical bonds. 

Ionic bonds are described as well. The transition from covalent over polar covalent to ionic bonds is veiy fluent and depends on the difference in electronegativity between the atoms. The covalent bonds consist of sharing an electron pair and ionic bonds are electrostatic interactions between a cation and an anion. Solid ionic compounds are often arranged in lattice structures with many similarities with the lattice structures that we saw for the metallic compounds. The type of lattice structure for solid ionic compound depends on the ration between the radius of the cation and anion. 

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