1 Chapter 5 Carbon: Addition Polymers, Elemental Forms, and Substituted Hydrocarbons From Diamonds to Plastics Copyright W. H. Freeman and Company · New York

2 Copyright W. H. Freeman and Company · New YorkChemistry Applied Hydrocarbons substituted by halogen atoms Addition polymers Physical properties of polymers Recycling of plastics Carbon networks Recycling of tires Familiar Metals: And their alloys, including mercury, gold and nickel in body studs Homogeneous Substances: Elements, compounds, atoms, molecules. Heterogeneous Mixtures: Colloids, especially emulsions in foods and lotions States of Matter: Including liquid crystals on TV and Copyright W. H. Freeman and Company · New York

3 Organic Molecules Containing Halogen AtomsHalogen atoms can substitute for hydrogen in simple alkanes. Methyl bromide, CH3Br is a naturally occurring substance formed naturally in the oceans. It is also produced synthetically for use in sterilizing soil prior to planting crops, although this use is restricted due to the threat of Ch3Br to the ozone layer. Copyright W. H. Freeman and Company · New York

4 Organic Molecules Containing Halogen AtomsAll four of the methane’s hydrogen atoms are equivalent so only one isomer of methyl bromide exists. Other similar molecules exist where the bromine atom is replaced by fluorine, chlorine, or iodine. Copyright W. H. Freeman and Company · New York

5 Organic Molecules Containing Halogen AtomsOther compounds of methane exist where several hydrogen atoms are replaced by halogen atoms. One example is methylene chloride, CH2Cl2, which is used as a common industrial and household solvent. There are several ways to draw the structure of methylene chloride in two dimensions on a sheet of paper, however there is only one isomer of methylene chloride. Copyright W. H. Freeman and Company · New York

6 Organic Molecules Containing Halogen AtomsHigher numbers of halogen atoms are also possible. Chloroform and carbon tetrachloride are common examples. Both are used as solvents for many organic compounds. Carbon tetrachloride was formerly used as a solvent, especially for dry cleaning, and as the liquid in some fire extinguishers but has been phased out for environmental reasons. Reactivity decreases with the number of chlorine atoms. Carbon tetrachloride is very unreactive chemically. Copyright W. H. Freeman and Company · New York

7 Organic Molecules Containing Halogen AtomsChloroform was previously used as an anesthetic. But has been phased out due to association with liver damage and the ease of administering an overdose. A modern multi-halogenated alkane still used as an anesthetic is halothane: CF3−CHBrCl. Copyright W. H. Freeman and Company · New York

8 Organic Molecules Containing Halogen AtomsCFCs had many uses but damage the atmospheric ozone layer. Alkanes in which two different halogens have been substituted for hydrogen atoms have also been prepared. Freon-12 and Freon-11 are two of these: Copyright W. H. Freeman and Company · New York

9 Organic Molecules Containing Halogen AtomsThese molecules are nonflammable, nontoxic, and boil below room temperature and were commonly used as refrigerants in air conditioners, propellants in spray cans, and the gas which created the holes in foam products made from liquids. Unfortunately, these molecules can catalytically destroy the ozone in the ozone layer and persist in the upper atmosphere for many years. Their use has been discontinued in most developed countries. The use of the related compound, halon, CF3Br, once used in some fire extinguishers has also been discontinued. Copyright W. H. Freeman and Company · New York

10 Organic Molecules Containing Halogen AtomsChlorine-substituted ethenes form the basis of many plastics and solvents. One of the simplest halogen substituted ethenes is chloroethene, also known as vinyl chloride: Again substitution at any of the four hydrogens of ethene results in exactly the same isomer. Vinyl chloride is the starting material for PVC or polyvinylchloride, one of the most common plastics. Copyright W. H. Freeman and Company · New York

11 Organic Molecules Containing Halogen AtomsSubstitution of three of the hydrogens in ethene results in trichloroethene (TCE): It is a commonly used solvent which used to be used for a variety of processes such as dry cleaning, grease stripping, paint stripping, and coffee decaffeination. It has been replaced for many of these uses for environmental reasons. Trichloroethene is very stable and is now a common pollutant of groundwater due to its extensive prior use. Copyright W. H. Freeman and Company · New York

12 Organic Molecules Containing Halogen AtomsSubstitution of all four of the hydrogens in ethene results in perchloroethene (TCE): It is also a commonly used solvent . Perchloroethene is very stable and is also a common pollutant of groundwater due to its extensive use. Copyright W. H. Freeman and Company · New York

13 Copyright W. H. Freeman and Company · New YorkAddition Polymers Very long chains of atoms with the same structural unit repeating over and over are called polymers. The chain length is 1000’ s of atoms rather than a dozen or two. Polymer research was carried out to find useful plastics and synthetic fibers. Plastics are materials that can be molded. They also have other advantages over natural materials: Do not rust Do not corrode or break easily Can be permanently colored Thermoplastics are those that become soft at high temperatures, where they can be molded. Copyright W. H. Freeman and Company · New York

14 Copyright W. H. Freeman and Company · New YorkAddition Polymers Polyethylene is the simplest organic polymer. Polyethylene, also called polyethene and polythene, is the simplest polymer. It is simply a mixture of alkanes of slightly different length, all about 20,000 carbon atoms long. The molecules are unbranched and pack very well together, similar to pencils in a box. In this high density form polyethylene is known as high-density-polyethylene or HDPE. Polyethylene is opaque and possesses considerable structural strength, toughness and rigidity. Copyright W. H. Freeman and Company · New York

15 Copyright W. H. Freeman and Company · New YorkAddition Polymers Addition polymers consist of repeating molecules joined together. In many polymers, some or all of the hydrogen atoms have been replaced by other atoms or groups of atoms. In the case that a hydrogen is replaced on every second carbon atom, the structure would look like: Copyright W. H. Freeman and Company · New York

16 Copyright W. H. Freeman and Company · New YorkAddition Polymers This can be thought of as the polymer: where −M− stands for: which is the repeating unit of the polymer. Copyright W. H. Freeman and Company · New York

17 Copyright W. H. Freeman and Company · New YorkAddition Polymers These polymers are know as addition polymers since they consist of intact individual monomers that combine together. In the above case, the monomer would be: Note that the double bonds in the monomer become single bonds in the polymer. Copyright W. H. Freeman and Company · New York

18 Copyright W. H. Freeman and Company · New YorkAddition Polymers The class of addition polymers derived from C=C units are called polyolefins. One of the most useful of these is PVC or polyvinylchloride. This polymer is built from vinyl chloride monomers: PVC plastics are rigid and strong. They are used in floor tiles, pipes, siding, and can also be made flexible enough to use in hoses and clothing. Copyright W. H. Freeman and Company · New York

19 Copyright W. H. Freeman and Company · New YorkAddition Polymers The flexibility in PVC is obtained by the addition of a plasticizer: a liquid that blends with the polymer and acts as a lubricant between the polymer molecules. Plasticizers eventually leak out of the plastics which then become brittle and break. Plasticizer leakage also results in environmental pollution. Copyright W. H. Freeman and Company · New York

20 Copyright W. H. Freeman and Company · New YorkAddition Polymers In polypropylene, a hydrogen atoms on the carbon chain are replaced by methyl groups. The monomer for this type of plastic is propylene: CH2=CHCH3. The properties of polypropylene are similar to those of polyethylene, however it can be heated to a higher temperature before softening. It is used where materials must be sterilized, such as medical syringes or dishwasher save plastics. Copyright W. H. Freeman and Company · New York

21 Copyright W. H. Freeman and Company · New YorkAddition Polymers Synthetic fibers made from polymers such a polypropylene are formed by squeezing molten polymer or polymer dissolved in a liquid through a small hole in a spinneret. The fibers then solidify and are stretched to make them strong. Some HDPE fibers have a tensile strength 20 times that of steel. Copyright W. H. Freeman and Company · New York

22 Copyright W. H. Freeman and Company · New YorkAddition Polymers Polystyrene is a polymer in which a hydrogen atom on every other carbon in the polymer chain is replaced by a benzene ring. It is a transparent, hard, brittle polymer and can be molded into many shapes. It is often encountered as a foam such as in coffee cups, egg cartons, packing materials, and “peanuts”. Research is underway to replace this and other non-degrading polymers with new polymers that break down under the action of sunlight or water. Copyright W. H. Freeman and Company · New York

23 Copyright W. H. Freeman and Company · New YorkAddition Polymers Polyvinylidene Chloride is produced from the monomer vinylident chloride. This polymer resists penetration by oxygen but is too rigid to be useful. Copyright W. H. Freeman and Company · New York

24 Copyright W. H. Freeman and Company · New YorkAddition Polymers To retain the oxygen penetration resistance and at the same time make the plastic more flexible, a copolymer between vinylidene chloride and vinyl chloride is produced: This copolymer can be made into a flexible film which is very impervious to oxygen and so will prevent food from spoiling. One brand name of this type of plastic is Saran. Copyright W. H. Freeman and Company · New York

25 Copyright W. H. Freeman and Company · New YorkAddition Polymers Polymerization of monomers having the formula: CX2=CX2 produce polymers having the structure: …-CX2-CX2-… The most important of these is Teflon: …-CF2-CF2-…, which has a very high resistance to chemical attack and thermal decomposition. It is most familiar as the non-stick surface on cooking pots and utensils. Teflon does decompose above 400o C so frying pans should not be heated above this temperature. Copyright W. H. Freeman and Company · New York

26 Copyright W. H. Freeman and Company · New YorkAddition Polymers Teflon fibers are used to make Gore-Tex brand clothing. This fabric repels liquid water but allows water molecules (from sweat) to readily pass through. Copyright W. H. Freeman and Company · New York

27 Properties of More Complex PolymersPolymers exist in two different solid states. Plastics can exist in the liquid state and in two different solid states. A transition between these two different solid states occurs at a specific temperature for each type of plastic called the glass transition temperature, Tg. An example of this transition is when a when certain flexible plastics become brittle when cooled. Copyright W. H. Freeman and Company · New York

28 Properties of More Complex PolymersA plastic, consisting of very long molecules of unequal length, cannot form normal crystals as can smaller molecules. Instead a plastic solid has many finite regions containing crystal-like order connected by regions of disorder. As the temperature is raised, the disordered, glass like, regions melt, however the crystal like regions remain in the solid state. This new state is called the rubber state and the plastic becomes flexible. Copyright W. H. Freeman and Company · New York

29 Properties of More Complex PolymersOne form of polyethylene is a branched polymer. In low density polyethylene a small percentage of carbon atoms along the chain have one of their hydrogen atoms replaced by an unbranched carbon chain about 4 carbons long. In addition the carbon chains are only about 500 atoms long rather than the 1000’s in HDPE. These molecules cannot pack together as efficiently and therefore have lower glass transition temperatures. Hot water is enough to deform materials made from this plastic. Copyright W. H. Freeman and Company · New York

30 Properties of More Complex PolymersRubber is a polymer chain that contains double bonds. Chemists have synthesized polymer chains where double bonds appear at regular intervals along the chain. These also occur naturally. In natural rubber, X is a –CH3 group. Copyright W. H. Freeman and Company · New York

31 Properties of More Complex PolymersNatural rubber becomes sticky and loses its natural resilience when heated. In 1839 Charles Goodyear discovered that the addition of elemental sulfur to natural rubber produced a substance that retained its desirable properties when heated. Cyclic S8 molecules open up to form chains of various lengths when heated. Copyright W. H. Freeman and Company · New York

32 Properties of More Complex PolymersSynthetic rubber can be made by polymerizing monomers such as butadiene, first made by German chemists in the 1930’s. Copyright W. H. Freeman and Company · New York

33 Properties of More Complex PolymersPolymers with alternating single and double bonds can conduct electricity. Polymerizing molecules such as acetylene, C2H2, results in a polymer containing alternating single and double bonds. This kind of polymer can conduct electricity and exhibits some characteristics of metal, such as luster. Electricity is not conducted over macroscopic distances, however because each molecule is short and there is now way for the electrons to jump from one molecule to the next. This problem can be alleviated by “doping” the polymer with small amounts of other substances which assist in transferring electrons between molecules. Copyright W. H. Freeman and Company · New York

34 The Recycling of PlasticsThe recycling of plastic is a controversial issue. The plastics industry argues that “virgin” plastic is a low cost material made from relatively low cost precursors, natural gas and petroleum. The cost of collection, cleaning and converting plastics back into monomer for reuse is substantial compared to the current cost of oil. They argue for the collection and burning of the plastics to utilize the heat energy provided. Environmentalists argue that environmental impacts have not been included in the cost analysis and the burning of some plastics releases toxic gases into the atmosphere. Copyright W. H. Freeman and Company · New York

35 The Recycling of PlasticsThere are several alternative ways to recycle plastics. There are four ways to recycle plastics: Reprocess by remelting or reshaping Production of plastic trash cans from recycled HDPE Depolymerize back into monomers. Difficult. Plasticizers and other substances must be removed. Yields of monomers are often low Transform into a lower-quality substance from which other materials can be made. React with oxygen and steam to produce synthesis gas. Heat to high temperature to “crack” the polymer molecules and produce synthetic crude oil. Burn to obtain energy Copyright W. H. Freeman and Company · New York

36 Copyright W. H. Freeman and Company · New YorkElemental Carbon Diamond: Its structure and bonding Consider a single with bonds to four other carbon atoms. In diamond, every carbon bonded to four other carbons in this way. Copyright W. H. Freeman and Company · New York

37 Copyright W. H. Freeman and Company · New YorkElemental Carbon The diamond lattice can be considered to consist of six membered rings, each fused to several neighboring rings by the sharing of two adjacent carbon atoms. Because the entire network of atoms is “welded” together as a unit, diamond is the hardest substance known. Copyright W. H. Freeman and Company · New York

38 Copyright W. H. Freeman and Company · New YorkElemental Carbon The formation and color of diamonds are dependent upon temperature and pressure. Diamond are formed km deep in the Earth’s mantle from carbon containing material that is subjected to intense heat and pressure. Erupting volcanoes eject diamonds, along with rock, from the depths. Synthetic diamonds can be produced by subjecting carbon containing substances to very high temperatures and pressures in a molten metal such as nickel or iron. Graphite, the other allotropic form of carbon, is actually more stable than diamond at ordinary pressures, but because diamond is more dense, diamond is the more stable form at high pressures. Copyright W. H. Freeman and Company · New York

39 Copyright W. H. Freeman and Company · New YorkElemental Carbon Pure diamond is colorless. An color in a diamond is a result of impurities trapped in the crystal when the diamond was formed. Diamonds are poor conductors of electricity, but good conductors of heat. They feel cool to the touch because they transport heat away from your fingers quickly. Copyright W. H. Freeman and Company · New York

40 Copyright W. H. Freeman and Company · New YorkElemental Carbon Polycyclic aromatic hydrocarbons (PAHs) fuse benzene rings together. The simplest polycyclic aromatic hydrocarbon is naphthalene, C10H8. It consists of two benzene rings, fused by two adjacent carbon atoms on each ring. Copyright W. H. Freeman and Company · New York

41 Copyright W. H. Freeman and Company · New YorkElemental Carbon Naphthalene is a solid compound which melts at 90o C. The solid is quite volatile and sublimes over time. It is toxic to certain insects and is used in some brands of mothball and moth flakes. Copyright W. H. Freeman and Company · New York

42 Copyright W. H. Freeman and Company · New YorkElemental Carbon PAHs are carcinogenic environmental pollutants Polycyclic aromatic hydrocarbons in the environment result from sources such as gasoline and especially diesel combustion engines, cigarette smoke “tar”, charred or burnt food, burning wood or coal, and other combustion sources where not all of the carbon is converted to CO2. Many PAH’s are known to be carcinogenic, at least in test animals. The most notorious is benzo[a]pyrene, BaP Copyright W. H. Freeman and Company · New York

43 Copyright W. H. Freeman and Company · New YorkElemental Carbon Occupational exposure to PAH’s has been linked to cancer in humans. Chimney sweeps exposed to coal tar (Benzo[a]pyrene) Workers in the coal tar and oil refining industries in the late 19th century Modern workers in coke and gas production plants Evidence of an exposure link to cancer in the general population is less clear cut Cigarette smoke is strongly linked to cancer but contains many carcinogenic compounds besides PAH’s. Pollution from burning of coal and natural materials, consisting primarily of PAH’s, sulfur dioxide gas, and tiny suspended soot particles are suspected to be responsible for over one million deaths annually in China. Copyright W. H. Freeman and Company · New York

44 Copyright W. H. Freeman and Company · New YorkElemental Carbon Graphite consists of weakly linked giant planes of carbon atoms. Graphite consists of fused benzene rings extending indefinitely in two directions. Hydrogen atoms are only present at the edges of the plane of carbon atoms and will represent a very small fraction of the total atoms, if the plane is large. Graphite is almost entirely carbon atoms. Copyright W. H. Freeman and Company · New York

45 Copyright W. H. Freeman and Company · New YorkElemental Carbon Each carbon atom in graphite is attached to three other carbon atoms in the plane, one of which is attached by a double bond. This arrangement completes the octet for the carbon atom and no electrons are left to bond to atoms in adjacent planes of atoms. Different planes of carbon atoms are only weakly attracted to each other, and may easily slide past one another. Graphite makes a good lubricant. Copyright W. H. Freeman and Company · New York

46 Copyright W. H. Freeman and Company · New YorkElemental Carbon Graphite conducts electricity in a direction along the planes, but not perpendicular to the planes. High strength fibers of graphite, encased in a plastic medium to protect them are used in products such as tennis racket frames. In general these mixtures of non-metallic materials are called composite materials. Copyright W. H. Freeman and Company · New York

47 Copyright W. H. Freeman and Company · New YorkElemental Carbon Impure forms of elemental carbon include soot, carbon black, and coke. Several impure forms of carbon are variations of graphite. Soot consists of tiny graphite crystal but in which about 10% of the atoms are hydrogen. The outside layers can readily adsorb organic molecules such as PAH’s. Carbon black is a pure form of soot consisting of tiny spheres and aggregates of the spheres. It is used as a pigment in ink and paint, and also to reinforce and color tires for vehicles. Coke, made by heating coal in the absence of air contains up to 98% carbon. It is used in industry as a cheap form for carbon. Copyright W. H. Freeman and Company · New York

48 Copyright W. H. Freeman and Company · New YorkElemental Carbon Activated carbon is a form of charcoal that is used to remove pollutants. Charcoal is an impure form of carbon made by heating wood in the absence of air. It has a very low density due to its highly porous nature, similar to a sponge. The many tiny holes and channels give charcoal a very large surface area which allows it to adsorb large amounts of other substances. When cleaned with steam, charcoal is called activated charcoal which has many applications, such as removal of contaminants from vapors and liquids, such as drinking water. Copyright W. H. Freeman and Company · New York

49 Copyright W. H. Freeman and Company · New YorkElemental Carbon Fullerenes are synthetic molecules containing many carbon atoms. Several molecular forms of carbon were discovered, starting in All are based on the graphite network structure. Nanotubes are tubes of carbon atoms a few nanometers in diameter and up to 100 micrometers long. Copyright W. H. Freeman and Company · New York

50 Copyright W. H. Freeman and Company · New YorkElemental Carbon On average about a dozen six membered rings are wrapped around the circumference of a nanotube. The ends of the nanotubes involve both five and six membered carbon rings. Five membered rings are easier to distort than six membered rings. Copyright W. H. Freeman and Company · New York

51 Copyright W. H. Freeman and Company · New YorkElemental Carbon Some nanotubes are so long that they act like ropes. Other nanotubes conduct electricity and heat very well. When open at one end they may provide a future high density storage medium for gaseous hydrogen. Combined with other synthetic materials they may create very strong, lightweight substances. Copyright W. H. Freeman and Company · New York

52 Copyright W. H. Freeman and Company · New YorkElemental Carbon Buckyballs are essentially two nanotube ends or caps without the nanotube itself. The molecular formula of buckminsterfullerene is C60. The molecule is shaped like a soccer ball whose seams correspond to the bonds in buckminsterfullerene. Copyright W. H. Freeman and Company · New York

53 Copyright W. H. Freeman and Company · New YorkRecycling of Tires An average of about one 10-kilogram rubber tire per person is discarded annually in North America. This represents one third of a billion tires added to a stockpile of about one billion used tires stored in huge “tire mountains”. Current recycling applications only consume about 10% of the tires discarded annually. Attempts to remove the sulfur in tires through vulcanization have recently succeeded. The process may or may not be commercially viable. Thermal decomposition, or pyrolysis, in the absence of oxygen converts the tires into low grade gaseous and liquid fuels and char. Char is a mixture of minerals and low grade carbon black which processed into a more uniform and purer form. Copyright W. H. Freeman and Company · New York

54 Copyright W. H. Freeman and Company · New YorkRecycling of Tires The rubber in tires is about 62% hydrocarbon polymer and 31% carbon black. There is a ready made market for carbon black. The liquid component of char contains a high percentage of aromatic hydrocarbons so burning as a fuel is problematic. Used tires have been used to build homes and in consumer products such as doormats and shoe soles. Copyright W. H. Freeman and Company · New York

55 Summarizing the Main IdeasHalogen atoms can substitute for any or all of the hydrogens in a hydrocarbon. Chlorine substituted hydrocarbons are often used as organic solvents. Addition polymers consist of very long chains of carbon atoms where the same basic structural unit, the monomer, repeats over and over. Addition polymers containing single bonds between all of the carbon atoms can be may by polymerizing properly substituted ethenes. Polymers are often made into plastics or fibers. Plasticizers are often added to polymers to make them more flexible. Fibers are made by extruding a melted polymer through a small hole in a spinneret and drawing the resulting material into a long fiber. Copyright W. H. Freeman and Company · New York

56 Summarizing the Main IdeasFoams are made by impregnating a polymer with beads of a substance that becomes a gas when heated, which forms bubbles in the polymer. Polymers exist in two different solid like states. At low temperature they are in the glass state, and above the glass transition temperature they are in the rubber state. In the rubber state, regions of disordered polymer melt and become liquid like, while regions of more ordered polymer remain in the solid state. In some polymers, including rubber, double bonds link some of the carbon atoms in the backbone chain. During the vulcanization of rubber, some of the carbon backbone chains are cross-linked by short chains of sulfur atoms. Copyright W. H. Freeman and Company · New York

57 Summarizing the Main IdeasPlastics can be recycled, however the subject is controversial. The four ways of recycling are: reprocessing, depolymerizing, transforming, and burning. Elemental carbon can exist in several allotropic forms Diamond – an extended 3D network of tetrahedral carbon atoms Graphite – an extended 2D network of carbon atoms organized into fused six member rings Nanotubes – long cylinders of graphite like carbon atoms, capped at the ends by oval caps containing 5 membered rings Buckyballs – a round structure whose formula is C60 A number of impure forms of carbon also exist. The most useful of these is activated charcoal. Copyright W. H. Freeman and Company · New York