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Metals are shiny, malleable (can be hammered into a shape), ductile (can be drawn in to a wire), thermally conductive (transfers heat), and electrically conductive (transfers electricity) materials. Only the coinage metals—copper, silver, and gold—are normally found in their metallic state. Other metals are easily oxidized by atmospheric oxygen to their ionic state.

As technology has advanced, so has our ability to produce metals for a variety of uses. Since copper is relatively abundant (compared with silver and gold) and can be found as a metal in its native state, it was one of the first commonly used metals. Melting copper with other metals produced alloys (homogeneous solutions of metals), which not only melted at lower temperatures, but also were harder. As higher temperature forges were introduced, an even harder metal, iron, was reduced to the metal from the ore. The addition of carbon to the iron produced the stronger alloy of steel. Eventually, the light-weight metal aluminum was produced by electrolysis.

Since alloys are solutions, they normally melt at lower temperatures than the pure metal, because of freezing point depression. This makes them easier to work with. Alloying with other metals can also change such properties as hardness and conductivity. For example, stainless steel—an alloy of iron, chromium, and nickel—is desirable for its resistance to corrosion. There are several types of alloys. In substitutional alloys, a metal atom replaces another similarly sized atom in the structure. Intermetallic compounds have a specific structure and therefore a constant composition. Interstitial alloys have the solute metal atoms occupying holes in the close-packed structure of the solvent metal.

Malleability is one of the more useful properties of metals. Metals can be hammered into other shapes because of plastic deformations which are locations where the pattern of the metal atoms is disrupted. For example, a line of the close-packed structure might be shifted out of the close-packed arrangement. These defects allow metal atoms to move with the application of force. Hammering actually increases the number of plastic deformations; however, when the defects intersect (are pinned), the movement of metal atoms is impeded. Therefore hammering can cause the metal to become less malleable, or work-hardened.

Ceramics are made from heated clay. A common variety of clay is kaolinite, Al₂Si₂O₅(OH)₄. Kaolinite is a variety of silicia, where some of the silicon atoms have been replaced with aluminum. This disrupts the tetrahedral structure so that kaolinite has a layered structure. Water absorbs between these layers, making the clay pliable, so that it can be shaped on a wheel or in a mold. The shaped clay is then heated or fired to change its composition and create a hard, chemically resistant material. Heating the material to 100 °C removes the surface water and the pliability of the material. Further heating to 450 °C removes the water between the layers. At about 600 °C, the actual composition of the clay begins to change. Hydroxides are removed from the aluminum atoms, Al₂Si₂O₇. At even higher temperatures (about 1000 °C) the structure changes to a spinel, Al₄Si₃O₁₂. At even higher temperatures, the structure changes to that of mullite, Al₆Si₂O₁₃.

Kaolinite mixed with water may form a colloid. Unlike in a solution, where the particles (ions or molecules) are mixed on a molecular level, a colloid is a solution of 1–1000 nm aggregates of particles. Colloids are stable. The particles do not settle out as with a suspension. The random or Brownian motion of the particles keeps them suspended in the solution. Colloidal solutions normally demonstrate the Tyndall effect. The Tyndall effect is caused by the scattering of light by the colloidal particles. Therefore light beams are actually visible as they pass through colloidal solutions.

Normally, ceramics are electrical and thermal insulators, and many uses have been based on these properties. However, at low temperatures, some ceramics become superconductors. At low temperatures, the electrical resistance of this type of material becomes zero. This property of ceramics is thought to be due to the formation of Cooper pairs, which are pairs of electrons that move in tandem rather than independently. Since an electron's random motion is restricted by the presence of the other electron of the Cooper pair, both electrons move more efficiently. In addition to zero resistance, superconductors exhibit Meissner effect, in which a magnet will levitate over a superconducting material. With no energy lost to thermal or random motion or even friction, superconductors are very efficient and therefore potentially very useful materials. Unfortunately, the critical temperature, the temperature at which a material becomes superconducting, is very low. Metals may become superconducting near 0 K. Some ceramics have critical temperatures near 77 K (temperature of liquid nitrogen), which is more useful. However, these low temperatures limit the practical uses of superconductors.

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Fibers are examples of polymers. Polymers are long chains of repeating units. The substances that link together to make a polymer are called monomers. Natural polymers include silk, wool, and cotton. Silk and wool are examples of polypeptides, which are made of amino acids joined with a peptide bond (Chapter 12). The primary structure of a polypeptide (or protein) is the chemical formula, the elements or amino acids in the chain. The secondary structure is the order of the amino acids. The tertiary structure is how the amino acids are arranged in space. The tertiary structure is often caused by hydrogen bonding between the side chains of the amino acids. Some of the tertiary structure of wool is also due to side chains with –SH groups reacting with other amino acids with –SH groups to make disulfide (CSSC) bonds.

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The tertiary structure of wool and silk is often coiled. Since breaking the hydrogen bonds is relatively easy, wool and silk stretch. The amount of stretch is measured as elongation. However, to break the fiber, covalent bonds must be broken. Tensile strength is the force required to break the fiber. Together these two properties, elongation and tensile strength, are called the modulus of elasticity.

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Cotton is a polysaccharide, a polymer of sugars. It has more hydrogen bonds than silk and wool, so it tends to be less elastic. The hydrogen bonds also allow it to absorb water readily. Cotton can be treated in a variety of ways to modify its properties. For example, mercerization involves treating cotton with a strong base. This removes H⁺, making ions. The ionic bonding is stronger than that of the hydrogen bonds. A more lengthy treatment of cotton (Figure 18) creates rayon.

The first synthetic polymer, nylon, was created by a condensation reaction and is thus a condensation polymer. Nylon is a polyamide, with amide bonds linking the monomers. The monomers have reactive groups (carboxylic acid or amine) on both ends of the carbon chain. Therefore condensation reactions occur at both ends and create a long chain linked by amide groups. Similarly, condensation reactions of monomers with carboxylic acid groups on each end create a polymer with ester links between monomers. Such condensation polymers are polyesters.

In addition polymerization the monomer reacts at only one end. In these reactions, an initiator creates a radical from an alkene. The radical reacts with the next alkene, linking the two together and creating another radical, which then reacts with another alkene. The reaction will continue until there are no more monomers to react with or a radical reacts with another radical, creating a bond and eliminating the radical. Often this polymerization creates a chiral carbon. If the chiral carbons all have the same stereochemistry (all R or all S), the polymer is called isotatic. If the stereochemistry varies, the polymer is atatic. Polymers can be made isotatic or atatic by controlling reaction conditions.