Ion—dipole forces

An Ion-dipole force exists between an ion and a polar molecule ( FIGURE 11.13). 

Cations are attracted to the negative end of a dipole, and anions are attracted to the positive end. The magnitude of the attraction increases as either the ionic charge or the magnitude of the dipole moment increases. Ion-dipole forces are especially important for solutions of ionic substances in polar liquids, such as a solution of NaCl in water. (Section 4.1) 

In which mixture do you expect to find ion-dipoie forces CH3OH in water or Ca(N03)2 in water  

Positive ends of polar molecules are oriented toward negatively charged anion 

Ion-dipole forces are important for solutions of ionic compounds in dipolar solvents, where solvated species such as Na(OH2) and C1(H20) (for solutions of NaCl in H2O) exist. In the case of some metal ions, these solvated species can be sufficiently stable to be considered as discrete species, such as [Co(NH3)6] or Ag(CFl3CN) 4. 

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Ion-Dipole Forces. Ion-dipole forces bring about solubihty resulting from the interaction of the dye ion with polar water molecules. The ions, in both dye and fiber, are therefore surrounded by bound water molecules that behave differently from the rest of the water molecules. If when the dye and fiber come together some of these bound water molecules are released, there is an increase in the entropy of the system. This lowers the free energy and chemical potential and thus acts as a driving force to dye absorption. 

Answer Ion-dipole forces and hydrogen bonding between H20 and the partially negative O atoms in Si02. ... 

Sodium chloride dissolves in water Ion-dipole forces of attraction between water molecules and ions are sufficient to overcome the forces between oppositely charged ions in the solid lattice. 

Whether the dissolving of a salt is exothermic or endothermic depends on the balance between the attractive forces of the crystal lattice and the ion-dipole forces that stabilize the ions in solution. 

Ions not solvated are unstable in solutions between them and the polar solvent molecules, electrostatic ion-dipole forces, sometimes chemical forces of interaction also arise which produce solvation. That it occurs can be felt from a number of effects the evolution of heat upon dilution of concentrated solutions of certain electrolytes (e.g., sulfuric acid), the precipitation of crystal hydrates upon evaporation of solutions of many salts, the transfer of water during the electrolysis of aqueous solutions), and others. Solvation gives rise to larger effective radii of the ions and thus influences their mobilities. 

An important extension of these ideas is to cases where an ion interacts with polar molecules (ion-dipole forces). In such cases the polarity of the molecule is increased because of the inductive effect caused by the ion. Polar solvent molecules that surround an ion in the solvation sphere do not have the same polarity as do the molecules in the bulk solvent. 

When an ionic compound is dissolved in a solvent, the crystal lattice is broken apart. As the ions separate, they become strongly attached to solvent molecules by ion-dipole forces. The number of water molecules surrounding an ion is known as its hydration number. However, the water molecules clustered around an ion constitute a shell that is referred to as the primary solvation sphere. The water molecules are in motion and are also attracted to the bulk solvent that surrounds the cluster. Because of this, solvent molecules move into and out of the solvation sphere, giving a hydration number that does not always have a fixed value. Therefore, it is customary to speak of the average hydration number for an ion. 

These types of attractions occur when the charge on an ion or a dipole distorts the electron cloud of a nonpolar molecule. This induces a temporary dipole in the nonpolar molecule. These are fairly weak interactions. Like an ion-dipole force, this type of force requires the presence of two different substances. 

For each of the substances the possible answers are ionic bonding, covalent bonding, metallic bonding, hydrogen bonding, dipole-dipole force, or London force. Forces, such as ion-dipole forces and ion-induced dipole forces, are not choices because these require the presence of two or more substances. For example, sodium chloride cannot utilize either of these two forces, but sodium chloride in water can. (Sodium chloride in water exhibits ion-dipole forces.)... 

In this chapter, you have learned about intermolecular forces, the forces between atoms, molecules, and/or ions. The types of intermolecular forces include ion-dipole forces, hydrogen bonding, ion-induced and dipole-induced forces, and London (dispersion) forces. 

Sodium chloride and other soluble ionic solids dissolve in polar solvents such as water because of ion-dipole forces. An ion-dipole force is the force of attraction between an ion and a polar molecule (a dipole). For example, NaCl dissolves in water because the attractions between the Na and Cl ions and the water molecules provide enough energy to overcome the forces that bind the ions together. Figure 4.14 shows how ion-dipole forces dissolve any type of soluble ionic compound. 

Ion-Dipole Model In this model ion-dipole forces are the principal forces in the ion-water interaction. The result of these forces is orientation of water molecules in... 

Just as two polar molecules, like opposite ends of a magnet, are attracted to each other, a polar molecule may be attracted to an ion. This gives rise to an ion-dipole force. The negative ends of polar molecules are attracted to cations and the positive end to anions. The charge on the ion and the strength of the dipole moment determine the... 

Ion a charged species created when an atom or group of atoms gains or loses electrons Ion-Dipole Force intermolecular force between an ion and a dipole Ion Pair in a solution when a positive and negative ion exist as a single particle Ion Product Constant in an ionic reaction, the product of each ion s concentration in solution raised to a power equal to the coefficient in the net ionic equation, for water it equals [H+][OH ]... 

The charges in sodium chloride are balanced, but they are not neutralized. As a water molecule gets close to the sodium chloride, it can distinguish the various ions and it is thus attracted to an individual ion by ion—dipole forces. This works because sodium and chloride ions and water molecules are of the same scale. We, on the other hand, are much too big to be able to distinguish individual ions within a crystal of sodium chloride. From our point of view, the individual charges are not apparent. 

When placed in an electric field, a dipole will attempt to orient and become aligned with the field. If the field results from an ion. the dipole will orient itself so that the attractive end (the end with charge opposite to that of the ion) will be directed toward the ion and the other, repulsive end directed away. In this sense, ion-dipole forces may be thought of as "directional," in that they result in preferred orientations of molecules even though electrostatic forces are nondirectional. 

Dipole-dipole interactions tend to be even weaker than ion-dipole interactions and to fell off more rapidly with distance (l/r3). Like ion-dipole forces, they are directional in the sense that there are certain preferred orientations and they are responsible for the association and structure of polar liquids. 

The insolubility of ionic compounds in nonpolar solvents is a similar phenomenon. The solvation energies are limited to those from ion-induced dipole forces, which are considerably weaker than ion-dipole forces and not large enough to overcome the very strong ion-ion forces of the lattice. 

The hydrated ion may be pictured as having a small number — possibly four or six — of water molecules firmly held in contact with the ion and constituting an inner shell, and a larger, less well defined, number more loosely held in an outer shell. Round a cation the inner shell water molecules are probably bonded by the strong ion-dipole force which operates when the water molecule is held in some such position as is indicated in formula (8). Anions are usually less hydrated than cations. The inner shell water molecules may not fit so well. Probably they are hydrogen bonded as shown in (9). In all cases, the outer shell water molecules are supposed to be hydrogen bonded to those of the inner shell. 

In this expression, Xj and (jl2 are the dipole moments of the interacting molecules. This expression shows that doubling the distance between the molecules reduces the strength of their interaction by a factor of 23 = 8. That strong dependence on distance means that the potential energy falls off much faster than the energies of ion-ion or ion-dipole forces (see Fig. 

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