Ionic electrical conductors

Electrolytes are distinguished from pure electronic conductors by the fact that the passage of an electric current is only insured by displacement of charged species called ions and hence accompanied by a transfer of matter. Therefore, electrolytes are entirely ionic electrical conductors without exhibiting any electronic conductivity (i.e., no free electrons). They can be found in the solid state (e.g., fluorite, beta-aluminas, yttria-stabilized zirconia, and silver iodide), liquid state (e.g., aqueous solutions, organic solvents, molten salts and ionic liquids), and gaseous state (e.g., ionized gases and plasmas). The ions (i.e., anions or cations)... 

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. 

C21-0093. Some pure liquid interhalogen compounds are good electrical conductors, indicating that they contain cations and anions. Show a Lewis acid-base reaction between two bromine trifluoride molecules that would generate ionic species. 

The zinc anode and copper cathode of a Daniell cell are both metals, and can act as electrical conductors. However, some redox reactions involve substances that cannot act as electrodes, such as gases or dissolved electrolytes. Galvanic cells that involve such redox reactions use inert electrodes. An inert electrode is an electrode made from a material that is neither a reactant nor a product of the cell reaction. Figure 11.6 shows a cell that contains one inert electrode. The chemical equation, net ionic equation, and half-reactions for this cell are given below. 

Electrical conductivity can also be an important consideration in p3rrotechruc theory [7]. This phenomenon results from the presence of mobile electrons in the solid that migrate when an electrical potential is applied across the material. Metals are the best electrical conductors, while ionic and molecular solids are generally much poorer, serving well as insulators. 

Heterophase assemblages of mixed ionic/electronic conductors of the type A/AX/AY/A under an electric load are the simplest inhomogeneous electrochemical systems that can serve to exemplify our problem. Let us assume that the transport of cations and electrons across the various boundaries occurs without interface polarization and that the transference of anions is negligible. For the other transference numbers we then have... 

Even though ionic solids are poor electrical conductors in the solid phase, they become good electrical conductors when dissolved in water. 

Ionic compounds are formed between metals and nonmetals. Metals don t hold onto their electrons very strongly (this is why they are good electrical conductors) and tend to form cations. Nonmetals are much better at attracting electrons and tend to form anions. 

Conductor — is a qualitative term reflecting the capability of a substance to conduct an electrical -> current. Depending on the type of sole or prevailing - charge carriers, - solid materials can be classified into ionic, electronic, and mixed ionic-electronic conductors. 

Ionic and mixed ionic-electronic conductors — Ionic conductors are solid systems that conduct electric current by movement of the ions. Mixed ionic-electronic conductors are those also conducting by the passage of electrons or holes (like metals or semiconductors). Usually only one type of ion (cation or anion) is predominantly mobile and determines conductivity. 

Sodium chloride is a typical ionic compound. Like most ionic compounds, it is a crystalline solid at room temperature. It melts at a very high temperature, at 801°C. As well, it dissolves easily in water. A solution of sodium chloride in water is a good conductor of electricity. Liquid sodium chloride is also a good electrical conductor. 

An applied electric field can be the electric held component of an electromagnetic wave, in which case electronic excitations or other optical responses may ensue. These are the topic of the next chapter. Here, the concern is with electrostatics, specihcally, the dielectric, or insulative, properties of materials. In an electrical conductor, an applied electric held, E, produces an electric current - ions, in the case of an ionic conductor, or electrons, in the case of an electronic conductor. Electrical conductivity has already been examined in earlier chapters. In insulating solids, the topic of the current discussion, the response to an applied electric held is a static spatial displacement of the bound ions or electrons, resulting in an electrical polarization, P, or net dipole moment (charge separahon) per unit volume, which is a vector quantity. In a homogeneous linear and isotropic medium, the polarization and electric held are aligned. In an anisotropic medium, this need not be so. The fth component of the polarization is related to the jth component of the electric held by ... 

Metallic bonds are generally weaker than either covalent or ionic bonds, which explains why metallically bonded minerals (true metals), like silver, gold, and copper, can be worked— beaten into flat sheets, or drawn into thin wires. In metallic bonds, electrons move about the crystal constantly flowing between adjacent atoms, redistributing their charge. Because of this flow of electrons, true metals are also good electrical conductors. 

Charged particles must be free to move for a material to conduct an electric current. In the solid state, ionic compounds are nonconductors of electricity because of the fixed positions of the ions. However, in a liquid state or when dissolved in water, ionic compounds are electrical conductors because the ions are free to move. An ionic compound whose aqueous solution conducts an electric current is called an electrolyte. You will learn more about solutions of electrolytes in Chapter 15. 

The strength and range of the electrostatic attractions make ionic crystals hard, high-melting, brittle solids that are electrical insnlators. Melting an ionic crystal, however, disrupts the lattice and sets the ions free to move, so ionic liquids are good electrical conductors. 

Ceramic electrochemical reactors are currently undergoing intense investigation, the aim being not only to generate electricity but also to produce chemicals. Typically, ceramic dense membranes are either pure ionic (solid electrolyte SE) conductors or mixed ionic-electronic conductors (MIECs). In this chapter we review the developments of cells that involve a dense solid electrolyte (oxide-ion or proton conductor), where the electrical transfer of matter requires an external circuitry. When a dense ceramic membrane exhibits a mixed ionic-electronic conduction, the driving force for mass transport is a differential partial pressure applied across the membrane (this point is not considered in this chapter, although relevant information is available in specific reviews). 

Because there are no ions in covalent compounds, you do not expect them to be electrical conductors. Ionic compounds tend to be soluble in water while molecular compounds do not. This difference is also explained by interparticle forces. Ions are attracted by water molecules, but many covalent molecules are not and, therefore, do not dissolve. Solubility in water and the nature of water solutions is a major topic in chemistry. You will learn more about solutions in Chapter 13. 

Disilver fluoride is a bronze-colored compound with a greenish cast when observed in bulk. It is an excellent electrical conductor. Crystal-structure determination3 shows the complete absence of elemental silver and silver(I) fluoride in the pure material and reveals the presence of successive layers of silver, silver, and fluorine in the lattice. The silver-silver distance is 2.86 A. (nearly twice the metallic radius of 1.53 A.), and the silver-fluorine distance is 2.46 A. [as in ionic silver(I) fluoride]. The compound is regarded as being intermediate in structure between a metal and a salt.4... 

When the atoms of a solid are joined by either ionic (electron transfer) or homopolar (electron sharing) forces the crystals have no free electrons. Such solids, e.g. sodium chloride and diamond, are either very poor electrical conductors or insulators. It is, of course, well known that sodium chloride and other similar ionic salts, when in the fused condition, are good electrical conductors it must be remembered, however, that under these conditions they owe their conducting powers to the presence of comparatively free ions, and it is these ions which actually transport the current. 

Unlike ionic compounds, most covalent substances are poor electrical conductors, even when melted or when dissolved in water. An electric current is carried by either mobile electrons or mobile ions. In covalent substances the electrons are localized as either shared or unshared pairs, so they are not free to move, and no ions are present. 

Ionic Positive and negative ions Ion-ion attraction Hard and brittle, high mp, good thermal and electrical conductors when molten NaCl [801] CaF2[1423] MgO [2852]... 

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