Covalent compound conductivity

In most covalent compounds, the strong covalent bonds link the atoms together into molecules, but the molecules themselves are held together by much weaker forces, hence the low melting points of molecular crystals and their inability to conduct electricity. These weak intermolecular forces are called van der WaaFs forces in general, they increase with increase in size of the molecule. Only... 

Aluminum nitride is a highly stable covalent compound with the unusual combination of high thermal conductivity (comparable to that of metals) and high electrical insulation (comparable to the... 

Although the covalent compounds of graphite are thus important in their own right, they represent the extreme form of oxidative intercalation. The use of fluoride compounds to achieve highly conductive materials may ultimately lead to new forms of graphite fluoride SI). 

Apparently 9-phenylfluorenyl is not only a good anion but also a bad cation. The chloride probably shares in some of the resonance stabilization of the anion while the cation does not. Another example of a connection between the resonance of an anion and the properties of a related covalent compound is provided by the hydrocarbon triphenyl-methylcyclopentadiene, which has an unusually high dipole moment although it does not conduct in liquid sulfur dioxide.180... 

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. 

Compounds like alcohols are nonelectrolytes—substances than do not conduct an electrical current when dissolved in water. However, certain covalent compounds, like acids, will ionize in water, that is, form ions ... 

As mentioned before, certain covalent compounds, like alcohols, readily dissolve in water because they are polar. Since water is polar, and these covalent compounds are also polar, water will act as a solvent for them (general rule of solubility Like dissolves like ). Compounds like alcohols are nonelectrolytes—substances that do not conduct an electrical current when dissolved in water. However, certain covalent compounds, like acids, will ionize in water, that is, form ions ... 

Covalent compounds, such as numerous halides of metals, give non-conducting solutions in these media. 

Electricity can also be generated inside a battery. A battery uses a chemical reaction to produce electricity. Inside a battery, there are two different metals in a chemical solution. A redox reaction occurs between the metals and the solution. This solution is called an electrolyte solution. An electrolyte is a substance that can conduct an electric current—the flow of electrons—when it is dissolved in water or melted. All ionic compounds are electrolytes. Most covalent compounds are not. 

Another troublesome borderline area is that between ionic solids and three-dimensional polymers. The distinction cannot be made from the structure alone. Electrical conductivity in the molten state does not, as already mentioned, necessarily demonstrate the presence of ions in the solid state and such a test is inapplicable where, as often happens, the substance sublimes or decomposes before melting. There can rarely be any objective means of assigning a compound to one category or the other. We are often persuaded towards one description on aesthetic grounds. For example, the structure of sodium chloride cannot easily be rendered in terms of localised, electron-pair bonds (but this is true also of many unequivocally covalent compounds). Its structure is eminently plausible for an array of cations and anions, however. 

For example, hydrogen chloride, also known as hydrochloric acid, has a low melting point and a low boiling point. (It is a gas at room temperature.) These properties might lead you to believe that hydrogen chloride is a covalent compound. Hydrogen chloride, however, is extremely soluble in water, and the water solution conducts electricity. These properties are characteristic of an ionic compound. Is there a clear, theoretical way to decide whether the bond between hydrogen and chlorine is ionic or covalent The answer lies in a periodic trend. 

Finally, consider hydrogen chloride, or hydrochloric acid. Hydrogen has an electronegativity of 2.20, and chlorine has an electronegativity of 3.16. Therefore, the electronegativity difference for the chemical bond in hydrochloric acid, HC1, is 0.96. Hydrogen chloride is a gas at room temperature, but its water solution conducts electricity. Is hydrogen chloride a covalent compound or an ionic compound Its AEN can help you decide, as you will see below. 

Covalent compounds have a wider variety of properties than ionic compounds. Some dissolve in water, and some do not. Some conduct electricity when molten or dissolved in water, and some do not. If you consider only covalent compounds that contain bonds with an electronegativity difference that is less than 0.5, you will notice greater consistency. For example, consider the compounds carbon disulfide, CS2, dichlorine monoxide, C120, and carbon tetrachloride, CC14. What are some of the properties of these compounds They all have low boiling points. None of them conducts electricity in the solid, liquid, or gaseous state. 

How do we explain the low conductivity of these pure covalent compounds The atoms in each compound are held together by strong covalent bonds. Whether the compound is in the liquid, solid, or gaseous state, these bonds do not break. Thus, covalent compounds (unlike ionic compounds) do not break up into ions when they melt or boil. Instead, their atoms remain bonded together as molecules. For this reason, covalent compounds are also called molecular compounds. The molecules that make up a pure covalent compound cannot carry a current, even if the compound is in its liquid state or in solution. 

For example, sucrose molecules have a number of sites that can form a hydrogen bond with water to replace the attraction between the sucrose molecules. (See Figure 8.11.) The sucrose molecules separate and become hydrated, just like dissolved ions. The molecules remain neutral, however. As a result, sucrose and other soluble covalent compounds do not conduct electricity when dissolved in water. They are non-electrolytes. 

Most of the Group IA and IIA metals react with hydrogen to form metal hydrides. For all of the metals in these two groups except Be and Mg, the hydrides are considered to be ionic or salt-like hydrides containing H ions (see Chapter 6). The hydrides of beryllium and magnesium have considerable covalent character. The molten ionic compounds conduct electricity, as do molten mixtures of the hydrides in alkali halides, and during electrolysis of the hydrides, hydrogen is liberated at the anode as a result of the oxidation of H ... 

Hydrogen chloride in the gaseous or pure liquid state does not conduct electricity, and possesses all the properties of a covalent compound. When the gas is dissolved in water, the resulting solution is found to be an excellent conductor of electricity, and therefore contains a high concentration of ions. Evidently water, behaving as a base, has reacted with hydrogen chloride to form hydronium and chloride ions ... 

These are conductive, in some cases superconductive materials (such as K3C60 and Rb3C6o) and are of great interest in the field of materials science. These are principally ionic, rather than covalent compounds. The interested reader is encouraged to consult the reference below" for additional information about these compounds. 

Another difference in properties between ionic and covalent compounds is electrical conductivity. No solid compound will conduct electricity, because the particles are not free to move. They are locked into the lattice. 

If you melt the compound, or dissolve it in water, the particles become free to move. You can dip a positive and a negative electrode into the melt or the solution and see if it conducts. What you find is that covalent compounds do not conduct electricity, whereas ionic ones do. Once again this result is not unexpected, since covalent compounds are composed of neutral molecules which will not be attracted to the electrodes, whereas ionic compounds are made up of charged ions which will be attracted to them. 

Why do molten ionic compounds generally conduct electric current well, while molten covalent compounds generally do not ... 

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