Conduction, electrical ionic

K. J. Senecal, L. Samuelson, M. Sermett, and G. H. Schreuder-Gibson, Conductive (electrical, ionic and photoelectric) membrane articlers, and method for producing same, US Patent Application, 0045547 (2001). 

There are many compounds which do not conduct electricity when solid or fused indicating that the bonding is neither metallic nor ionic. Lewis, in 1916. suggested that in such cases bonding resulted from a sharing of electrons. In the formation of methane CH4 for example, carbon, electronic configuration l.s 2.s 2p. uses the tour electrons in the second quantum level to form four equivalent... 

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

Electrolyte a substance, liquid or solid, which conducts electrical current by movement of ions (not of electrons). In corrosion science, an electrolyte is usually a liquid solution of salts dissolved in a solvent, or a molten salt. The term also applies to polymers and ceramics which are ionically conductive. 

When an ionic solid such as NaCl dissolves in water the solution formed contains Na+ and Cl- ions. Since ions are charged particles, the solution conducts an electric current (Figure 2.12) and we say that NaCl is a strong electrolyte. In contrast, a water solution of sugar, which is a molecular solid, does not conduct electricity. Sugar and other molecular solutes are nonelectrolytes. 

Ionic solids do not conduct electricity because the charged ions are fixed in position. They become good conductors, however, when melted or dissolved in water. In both cases, in the melt or solution, the ions (such as Na+ and Cl-) are free to move through the liquid and thus can conduct an electric current. 

When an ionic solid like sodium chloride is melted, the molten salt conducts electric current. The conductivity is like that of an aqueous salt solution Na+ and Cl- ions are present. The extremely high melting temperature (808°C) shows that a large amount of energy is needed to tfear apart the regular NaCl crystalline arrangement to free the ions so they can move. 

Answer (a) Ionic compound, so a strong electrolyte, conducts electricity ... 

All metals conduct electricity on account of the mobility of the electrons that bind the atoms together. Ionic, molecular, and network solids are typically electrical insulators or semiconductors (see Sections 3.f3 and 3.14), but there are notable exceptions, such as high-temperature superconductors, which are ionic or ceramic solids (see Box 5.2), and there is currently considerable interest in the electrical conductivity ol some organic polymers (see Box 19.1). 

In contrast to sugar, solid sodium chloride dissolves in water to give a liquid that conducts electricity. Figure 3-19 shows that a solution of NaCl is a good conductor. When an ionic compound dissolves in water, its component cations and anions are free to move about in the solution. Mixing leads to a uniform distribution of Na and Cl ions through the entire solution, with each ion surrounded by a sheath of water molecules as shown in Figure 3-20. 

The presence of ions in solution is what gives a sodium chloride solution the ability to conduct electricity. If positively and negatively charged wires are dipped into the solution, the ions in the solution respond to the charges on the wires. Chloride anions move toward the positive wire, and sodium cations move toward the negative wire. This directed movement of ions in solution is a flow of electrical current. Pure water, which has virtually no dissolved ions, does not conduct electricity. Any solution formed by dissolving an ionic solid in water conducts electricity. Ordinary tap water, for example, contains Ionic Impurities that make It an electrical conductor. 

This is the last bond type to be considered. Let s start with a question What holds a metal together A bar of copper or magnesium has properties that are entirely different from substances held together by ionic or covalent bonds. Metals are dense structures that conduct electricity readily. They are malleable, which means that they can be easily twisted into shapes. They are ductile, which allows them to be drawn into wires. No substances with ionic or covalent bonds, such as salt or water, behave anything like metals. 

One clue to understanding the nature of metallic bonds comes from their high electrical conductivity. Like most substances held together by ionic or covalent bonds, pure water and pure salt do not conduct electricity well. But pure copper does. Electrical conductivity is a measure of how free the electrons are to move. The high conductivity of metals indicates that their electrons are freer to move than the electrons are in salt or water. 

Recognizing Cause and Effect In a crystal lattice structure, the electrons are held tightly by the ions, which are rigidly held in place by electrostatic attraction. Discuss how this characteristic explains why ionic compounds generally (a) have high melting points and (b) do not conduct electricity in the solid state. 

Thinking Critically Explain how ionic compounds, which do not conduct electricity in the solid form, can conduct electricity when they are in the molten state or dissolved in water. 

This equation is valid for both strong and weak electrolytes, as a = 1 at the limiting dilution. The quantities A = zf- FU have the significance of ionic conductivities at infinite dilution. The Kohlrausch law of independent ionic conductivities holds for a solution containing an arbitrary number of ion species. At limiting dilution, all the ions conduct electric current independently the total conductivity of the solution is the sum of the contributions of the individual ions. 

An important developing area that lies in the region between polymer chemistry, ceramic science, and metals, involves the search for new electrically-conducting solids. Linear polymers may conduct electricity by electronic or ionic mechanisms. As will be discussed, polyphosphazenes have been synthesized that, depending on the side group structure, conduct by either of these two processes. 

We shall briefly discuss the electrical properties of the metal oxides. Thermal conductivity, electrical conductivity, the Seebeck effect, and the Hall effect are some of the electron transport properties of solids that characterize the nature of the charge carriers. On the basis of electrical properties, the solid materials may be classified into metals, semiconductors, and insulators as shown in Figure 2.1. The range of electronic structures of oxides is very wide and hence they can be classified into two categories, nontransition metal oxides and transition metal oxides. In nontransition metal oxides, the cation valence orbitals are of s or p type, whereas the cation valence orbitals are of d type in transition metal oxides. A useful starting point in describing the structures of the metal oxides is the ionic model.5 Ionic crystals are formed between highly electropositive... 

In ionic solids, electrons are held in place around the ions so they don t conduct electricity. However, in aqueous solution and molten state, they do conduct electricity. Electrical conductance of ionic compounds is not due to movement of electrons but to the movement of ions. 

KC1, NaNOs and LiF are ionic solids. Ionic solids don t conduct electricity in the solid state, however, aqueous solutions and molten forms of ionic compounds contain mobile ions so they can conduct electricity Thus, aqueous KC1 and LiF conduct electricity but solid NaN03 doesn t. 

Ionic Compounds (Ex NaCl, BaCl2, KN03) Electrostatic Positive and negative ions - hard and brittle - high melting point - aqueous solutions and molten states conduct electricity... 

Many of the reactions that you will study occur in aqueous solution. Water readily dissolves many ionic compounds as well as some covalent compounds. Ionic compounds that dissolve in water (dissociate) form electrolyte solutions— solutions that conduct electrical current due to the presence of ions. We may classify electrolytes as either strong or weak. Strong electrolytes dissociate (break apart or ionize) completely in solution, while weak electrolytes only partially dissociate. Even though many ionic compounds dissolve in water, many do not. If the attraction of the oppositely charged ions in the solid is greater than the attraction of the water molecules to the ions, then the salt will not dissolve to an appreciable amount. 

Reversed-phase separations currently dominate in CEC. As a result, the vast majority of the mobile phases are mixtures of water and an organic solvent, typically acetonitrile or methanol. In addition to the modulation of the retention, the mobile phase in CEC also conducts electricity and must contain mobile ions. This is achieved by using aqueous mixtures of salts instead of pure water. The discussion in Sect. 2 of this chapter indicated that the electro osmotic flow is created by ionized functionalities. The extent of ionization of these functionalities that directly affects the flow rate depends on the pH value of the mobile phase. Therefore, the mobile phase must be buffered to a pH that is desired to achieve the optimal flow velocity. Obviously there are at least three parameters of the mobile phase that have to be controlled (i) percentage of the organic solvent, (ii) the ionic strength of the aqueous component, and (iii) its pH value. 

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