Ionic bonds forces

The familiar Lewis structure is the simplest bonding model in common use in organic chemistry. It is based on the idea that, at the simplest level, the ionic bonding force arises from the electrostatic attraction between ions of opposite charge, and the covalent bonding force arises from sharing of electron pairs between atoms. 

The term subsidiary valency forces is also used to indicate the interaction through Van der Waals forces, including the hydrogen bond formation (p. 369) in contrast to the stronger atomic and ionic bonding forces. Thus one says that the bonding in one molecule of a polymer is due to principal valency forces, the mutual connection between the molecules is attributed to the so-called subsidiary valency forces. 

From a consideration of ionic bonding forces, Krasnov and Karaseva (4) calculated 55 10 kcal mol... 

The discussions of ionic bonding forces in Chapter 3 and of dispersion forces in Chapter 4 pointed out that those forces can form bonds between indefinite numbers of atoms. They are indiscriminate in their operation and find their only limitation in the fact that the sizes of atoms limit the number that can cluster about any one atom. Since those forces all fall off with increasing distance, their bonds are strongest between nearest neighbours. 

Atoms combine with one another to give compounds having properties different from the atoms they contain The attractive force between atoms m a compound is a chemical bond One type of chemical bond called an ionic bond, is the force of attraction between oppositely charged species (ions) (Figure 1 4) Ions that are positively charged are referred to as cations, those that are negatively charged are anions... 

FIGURE 1 4 An ionic bond IS the force of attrac tion between oppositely charged ions Each Na ion (yellow) in the crystal lattice of solid NaCI IS involved in ionic bonding to each of six surrounding Cl ions (green) and vice versa... 

Were we to simply add the ionization energy of sodium (496 kJ/mol) and the electron affin ity of chlorine (—349 kJ/mol) we would conclude that the overall process is endothermic with AH° = +147 kJ/mol The energy liberated by adding an electron to chlorine is msuf ficient to override the energy required to remove an electron from sodium This analysis however fails to consider the force of attraction between the oppositely charged ions Na" and Cl which exceeds 500 kJ/mol and is more than sufficient to make the overall process exothermic Attractive forces between oppositely charged particles are termed electrostatic, or coulombic, attractions and are what we mean by an ionic bond between two atoms... 

Section 1 2 An ionic bond is the force of electrostatic attraction between two oppo sitely charged ions Atoms at the upper right of the periodic table espe cially fluorine and oxygen tend to gam electrons to form anions Elements toward the left of the periodic table especially metals such as sodium tend to lose electrons to form cations Ionic bonds m which car bon IS the cation or anion are rare... 

Secondary Bonding. The atoms in a polymer molecule are held together by primary covalent bonds. Linear and branched chains are held together by secondary bonds hydrogen bonds, dipole interactions, and dispersion or van der Waal s forces. By copolymerization with minor amounts of acryhc (CH2=CHCOOH) or methacrylic acid followed by neutralization, ionic bonding can also be introduced between chains. Such polymers are known as ionomers (qv). 

Solid Dispersion If the process involves the dispersion of sohds in a liquid, then we may either be involved with breaking up agglomerates or possibly physically breaking or shattering particles that have a low cohesive force between their components. Normally, we do not think of breaking up ionic bonds with the shear rates available in mixing machineiy. 

So far, we have had to do work to create the ions which will make the ionic bond it does not seem to be a very good start. However, the + and - charges attract each other and if we now bring them together, the force of attraction does work. This force is simply that between two opposite point charges ... 

Sq can be calculated from the theoretically derived U(r) curves of the sort described in Chapter 4. This is the realm of the solid-state physicist and quantum chemist, but we shall consider one example the ionic bond, for which U(r) is given in eqn. (4.3). Differentiating once with respect to r gives the force between the atoms, which must, of course, be zero at r = rg (because the material would not otherwise be in equilibrium, but would move). This gives the value of the constant B in equation (4.3) ... 

X-ray structural studies have played a major role in transforming chemistry from a descriptive science at the beginning of the twentieth century to one in which the properties of novel compounds can be predicted on theoretical grounds. When W.L. Bragg solved the very first crystal structure, that of rock salt, NaCl, the results completely changed prevalent concepts of bonding forces in ionic compounds. 

Chemical bonds are strong forces of attraction which hold atoms together in a molecule. There are two main types of chemical bonds, viz. covalent and ionic bonds. In both cases there is a shift in the distribution of electrons such that the atoms in the molecule adopt the electronic configuration of inert gases. 

Electronic characteristics and their effects on the ability of side chains to engage in ionic bonding, covalent bonding, hydrogen bonding, van der Waals forces, and acid-base chemistry... 

Ionic compounds are held together by strong electrical forces between oppositely charged ions (e.g., Na+, Cl-). These forces are referred to as ionic bonds. 

We have considered the weak van der Waals forces that cause the condensation of covalent molecules. The formation of an ionic lattice results from the stronger interactions among molecules with highly ionic bonds. But most molecules fall between these two extremes. Most molecules are held together by bonds that are largely covalent, but with enough charge separation to affect the properties of the molecules. These are the molecules we have, called polar molecules. 

If you were given a sample of a white solid, describe some simple experiments that you would perform to help you decide whether or not the bonding involved primarily covalent bonds, ionic bonds, or van der Waals forces. 

What Do We Need to Know Already This chapter assumes that we are familiar with the concept of energy (Section A), stoichiometry (Sections L and M), and the ideal gas law (Chapter 4). Some of the explanations refer to intermolecular forces (Sections 4.12 and 5.1-5.5). Ionic bonding (Sections 2.3-2.4) and bond strengths (Sections 2.14-2.15) are developed further in this chapter. 

The four structures with three double bonds (third row) and the one with four double bonds are the most plausible Lewis structures, (b) The structure with four double bonds fits these observations best, (c) +7 the structure with all single bonds fits this criterion best, (d) Approaches (a) and (b) are consistent but approach (c) is not. This result is reasonable because oxidation numbers are assigned by assuming ionic bonding. 2.109 The alkyne group has the stiffer C—H bond because a large force constant, k, results in a higher-frequency absorption. 

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