By Bob Beckermilliga9.weebly.com/uploads/8/1/4/3/8143601/glass_article.pdfscene. He claims to be...

2 ChemMatters, OCTOBER 2006

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COVER ILLUSTRATION BY JIM NUTTLE

By Bob Becker

Question From the Classroom

http://chemistry.org/education/chemmatters.html

Q: My parents are looking into buying aheat pump. A brochure they got said that inthe winter, a heat pump takes heat from thecold outside air and pumps it into the house.In the summer, it pumps the heat from theinside air out. How can it do that?

A: As strange as this seems, that is fun-damentally how a heat pump works, but thetruth is, your family already owns a heat pump— in fact they probably own three or four.Your refrigerator and air conditioners — bothfor your house and for your cars — are heatpumps. They only work one way of course,but the principle is still the same.

So let’s take a look at how a refrigeratorworks first. The explanation begins (as allgood explanations do) at the molecular level,and what we will need is a substance with aboiling point about 50°C below room temper-ature. As you may have already learned, or willsoon, molecules are attracted to one another.In some substances the attractions are veryweak, like between two H2 molecules. Becausethe attractions between H2 molecules are soweak, the substance is a gas at room condi-tions and must be taken to extremely low tem-peratures before those attractions take overand allow it to condense into a liquid. Its boil-ing point is -253°C — way too low for ourpurposes. In other substances, like H2O, theintermolecular forces of attraction are sostrong that the substance is a liquid at roomtemperature, and must be heated up quite abit to convert it into a gas. The boiling point ofH2O is 100°C–way too high. Some com-pounds though, known as refrigerants, havejust the right amount of intermolecular attrac-tions to give them the optimum boiling points.Dichlorodifluoromethane (CCl2F2) — alsoknown as Freon-12 — is one such refrigerant,and it has a boiling point of -30°C (room tem-perature is about 20°C).

Now, when a substance boils, it changesfrom a liquid to a gas; its molecules are pulledaway from one another, and the attractionsbetween them are broken. This takes heatenergy in — we say the process is “endother-mic” — and that’s half of the story of how arefrigerator or heat pump works. If those

gaseous molecules are then pushed closertogether by a compressor, the intermolecularforces can take over and cause the substanceto condense back into a liquid. This processgives off heat; we say it is “exothermic” —and that is the other half of the story!

So, imagine some CCl2F2 under enoughpressure that it is in the liquid state, and thenhave it injected into a compartment that is notat high pressure. The liquid would immediatelyboil, taking in heat from the surroundings,making the compartment and the air around itget quite cold. Now move that gas through apipe and into a separate compartment where acompressor increases the pressure and con-denses it back into a liquid. This condensationwould release heat to the surroundings, mak-ing this compartment and the air around it getquite warm. Transferring this pressurized liq-uid back into the low pressure compartmentallows this whole cycle to start again.

This cycle takes place inside — andbehind — your refrigerator, and although it iscalled a “refrigerator,” it actually does asmuch heating up as it does cooling down. Gotouch the metal grate on the back side of yourfridge. The warmth you feel there is the heatreleased by the condensing refrigerant, andindirectly it is the heat that has been“pumped” out of your food and beverages!The grate has a lot of surface area to allowthe heat to dissipate quickly. An air condi-tioner works the same way: that big unit out-side your house is where the exothermiccondensation process occurs. And whenyou’re trying to cool down an entire housefull of air, heat dissipation becomes an evenbigger task. That is why there is a fan blowingair across the coils. Hold your hand over theunit and feel the heat being pumped out of

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Vol. 24, No. 3 OCTOBER 2006

ChemMatters, OCTOBER 2006 3

Question From the Classroom 2How does a heat pump work?

Glass: More Than Meets the Eye 4The sound of glass shattering. A scream in the night… Acts ofviolence often involve broken glass and it's a common type ofevidence found at crime scenes. How do forensic police matchsamples of glass?

ChemSumerChemistry Builds a Green Home 9It seems that everything is turning “green” these days. Whenthe concept is brought home, the results are impressive.Today’s homes can be both environmentally friendly andesthetically pleasing.

Sick Buildings—Air Pollution Comes Home 12When your parents tell you to go outside and get some freshair, are they really doing you a favor? Take a look at the toxinslurking around your home before you answer.

ChemHistoryThe New Alchemy 15The elements from hydrogen to uranium were created in the BigBang or afterward during the life cycles of stars, but what aboutthe transuranium elements, those that lie beyond uranium onthe periodic table? How were these artificial elements createdand who were the men and women responsible for theirdiscovery?

Material Safety Data Sheets: Passports to Safety? 18Next time you blow out a candle, will you be properly armedwith a self-contained breathing apparatus and dry chemical fireextinguisher? An MSDS is an important safety tool — but howdo you gauge the accuracy of the information it contains?

CMTEACHERS! FIND YOUR COMPLETE

TEACHER’S GUIDE FOR THIS ISSUE ATwww.chemistry.org/education/chemmatters.html.

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Check out these great Web sites:http://www.smeco.com/energy/heatpump/learn.htmlhttp://home.howstuffworks.com/question49.htmhttp://www.honeywell.com/sites/sm/410a/Air-Conditioners.htm

your house. Even when the outside tem-perature is at its highest, the air blowingout of that unit is hotter still. The boiling(endothermic) side of the cycle is notquite so accessible, but it is there —inside your house, in the duct work withthe air being cooled as it blows acrossthe coils.

So what exactly is special about aheat pump? A heat pump is simply an airconditioner that can be run in reverse. Inthe winter, with the refrigerant flowing theopposite direction, the condensing nowtakes place inside your house and pro-vides the warmth. Meanwhile, the boilingis going on outside your house and mak-ing the cold air out there even colder. Coolgas enters the compressor whichincreases the pressure (1). The gas, nowunder high pressure, condenses into a liq-uid making it very hot (2). Inside air iswarmed as it blows across the warm liq-uid (3). As the warm liquid passesthrough an expansion valve (4), the pres-sure is allowed to drop. Under reducedpressure, the liquid begins to boil andgets very cold (5). The gas is now heatedby the outside air that is blown across thecoils (6), and the process is repeated. Asstrange as this might seem, this methodof heating can be three to four times moreefficient than a conventional furnace, andthus with reduced energy bills, a heatpump can essentially pay for itself overthe years.

Furnaces generally produce heat thesame way ovens do—either by burningfuel (natural gas, propane, or oil) or bypassing high-voltage electricity through aresistor. Neither of these is as efficient asa heat pump. The one drawback, however,to heat pumps is that they do not work aswell below 0°C. At such low temperatures,ice begins to form on the outside coilsand this insulates them and prevents theheat from getting in. Many home-ownersare now installing dual systems: a heatpump for the summer and for the mildwinter days, and a conventional electricfurnace that automatically switches on forthe occasional deep freeze.

4 ChemMatters, OCTOBER 2006 http://chemistry.org/education/chemmatters.html

A23-year-old single female isawakened in the middle of thenight by an intruder standingover her bed. She screams. Theintruder flees in a panic, divingthrough a closed window. The

police are notified immediately. They appre-hend a suspect several blocks from thescene. He claims to be innocent, yet thepolice discover several shards of glass in thesuspect’s hair and clothing. When these sam-ples are compared to the glass of the brokenwindow, they are discovered to be the exactsame type of glass. On the basis of this evi-dence, the intruder is eventually convictedand sent to jail.

Because acts of violence often involvebroken glass, glass is one of the most com-monly encountered forms of evidence foundat crime scenes. However, many pieces ofglass appear identical to the naked eye eventhough they can differ markedly in their chem-ical composition.

How do forensic scientists matchsamples of glass?

Careful observation can reveal subtle butimportant differences between various typesof glass. The forensic chemist may use sev-eral methods for determining whether twosamples of glass originated from the samesource. The first step is to visually examinethe glass. Physical properties of the glass arethen measured. Subsequent steps involveanalysis of the chemical composition and dif-ferences in the way it was manufactured.

Physical examination

Some important features to note areedge thickness, color, and the presence ofany labels or imprints on the glass. A black-light lamp may be used to check for repairsas hairline cracks will glow under ultravioletlight. Modern paints will also glow under ablacklight.

ThicknessGlass thickness is generally a function

of its application. Glass from a light bulb isgoing to be thinner than a pane of window

glass. The glass used in a picture frame isgenerally not subject to gusts of wind, so itwill be thinner than glass used in a window.Glass used in a door is generally eventhicker, to withstand the forces applied as aresult of frequent opening and closing (andsometimes slamming!).

DensityOne of the most common methods for

matching glass samples is the determinationof density. The formula for density ismass/volume, and the density of two pieces ofglass will always be the same if they comefrom the same source, regardless of the sizeof the two pieces. The formula method fordetermining density involves measuring thevolume of a glass sample of known mass. Thevolume can be determined by displacing waterin a volumetric flask.

Another more accurate method of com-paring densities is the flotation method. Asample of glass is dropped into and sinks tothe bottom of a liquid containing an exact vol-ume of a dense liquid, such as bromobenzene(d = 1.52 g/mL). Then, a denser liquid, suchas bromoform (d = 2.89 g/mL) is added drop-wise until the piece of glass rises up from thebottom and attains neutral buoyancy. Neutralbuoyancy occurs when an object has the exact

More Than Meets the Eye

By Brian Rohrig


same density as the surrounding fluid, andneither sinks nor floats but is suspended inone place beneath the surface of the fluid.

The same procedure is then performedwith another piece of glass, and if the volumeneeded to attain neutral buoyancy is the sameas for the first sample, then the densities ofthe two samples are equal. The exact densityof each sample can be calculated by using thefollowing formula:

X and Y refer to the volumes of therespective liquids, with the numbers in paren-theses referring to the densities of each liquid.Any two liquids can be used, as long as theyare miscible in one another and have appro-priate densities. But when determining thedensity of glass, liquids with a relatively highdensity must be used, since glass is alwaysdenser than water. The density of a typicalpiece of single-pane window glass rangesfrom 2.47 to 2.56 g/mL. If the density of a1.5-g sample of glass were 2.48 g/mL, whatwould you predict the density to be for a 3.0-gsample of the same glass? (Find the answerat the conclusion of this article.)

Refractive indexAnother very accurate method used to

compare samples is to determine their indexof refraction, or refractive index. Any objectthat transmits light has its own refractiveindex, which is a measure of how much theobject slows the speed of light. When lightpasses through any medium, it is sloweddown. The denser the medium, the slower thelight travels. The refractive index of any sub-stance is a ratio of the velocity of light in avacuum to the velocity of light in that particu-lar medium. For example, the refractive indexfor water is 1.33. This means that light travels1.33 times faster in a vacuum than it does inwater. And when light passes from onemedium to another one with a different refrac-tive index, refraction (or bending) of the lightoccurs. This is why objects appear bent ordistorted under water.

Every liquid has its own refractive index.If a piece of glass is placed in a liquid with adifferent refractive index, an outline of theglass is clearly visible—known as the Beckeline. However, if a piece of glass is placed in aliquid with the same refractive index, theBecke line will disappear and the glass willseem to disappear. This is because the glassbends light at the same angle as the liquid.

Glycerin has a refractive index of 1.473.If a piece of glass seems to dissapear in glyc-erin, then it too has a refractive index of1.473. If two samples of glass have the samerefractive index, this does not necessarilyprove they are from the same source. But iftwo samples have different refractive indexes,they are definitely not from the same source.The FBI has a database of refractive index val-ues for approximately 2000 different types ofglass, allowing forensic scientists the ability toidentify samples. The most common value forthe refractive index of glass is 1.5180.

d = X(2.89) + Y(1.52)

X + Y

81.0 mL 86.5 mL

The beaker on the left contains water and theone on the right, glycerin. Both beakers alsocontain a glass stirring rod. Because the glassrod and glycerin have the same refractive index,the glass rod in the beaker on the right seems to “disappear.”

The formula method for determining density: After finding the mass of an object, measure its volume by water displacement.

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Chemical composition

If both the density and refractive index oftwo samples of glass are the same, then thefinal test will involve sophisticated methods todetermine their chemical composition. Thedifference between types of glass can be dueto the chemical composition of the glass itselfor differences in how the glass was manufac-tured. Most glass is made from silicon dioxide(SiO2), the primary ingredient in sand, whichhas been heated above its melting point of1600°C. Various substances are then added,depending on what type of glass is desired.

Different additives can impart differentproperties to the glass. Sodium carbonate orsoda (Na2CO3) is added to the silicon dioxideduring glassmaking, lowering both its viscos-ity and melting point. The soda increases thewater solubility of SiO2, making it much easierto fashion into glass. Calcium oxide or lime(CaO) is added next, restoring water insolubil-ity to the mixture. As a result of these twoadditives, most glass used to make windowsor bottles is known as soda-lime glass.

Boron oxide (B2O3) is used to makePyrex glassware. The beakers and test tubesyou use in chemistry lab are most likely madefrom Pyrex, as is the glass used to make autoheadlights. Glass made with boron oxideexpands and contracts very little when heatedand cooled, which is why Pyrex glassware canbe heated and then cooled without breaking.

To make eyeglasses, a very sturdy glassis desired, so the additive potassiumoxide (K2O) may be used. Thisimparts hardness to the glass. Othermetallic oxides can give glass a spe-cific color. Copper and cobalt oxidesare used to make glass blue, man-ganese oxides give glass a purplecolor, and lead-antimony oxideimparts an opaque yellow.

Who fired first?When a bullet strikes a pane of

ordinary window glass, careful obser-vation can reveal several crucialdetails. First of all, glass has a certaindegree of elasticity and will breakwhen this elastic limit is exceeded. This elas-ticity produces the familiar pattern of concen-tric and radial fractures that accompanypenetration of glass by a projectile. The radialfractures are produced first and always formon the side of the glass opposite to where the

impact originated. Radial fractures look likespider webs that spread outward from theimpact hole. Concentric fractures form next,and these lines encircle the bullet hole. Con-centric fractures always start on the same sideas that of the destructive force.

A radial fracture will always terminateinto an existing fracture (see illustration). Ifthere is a second bullet hole in a piece ofglass, its radial fractures will always terminateinto the cracks from the first bullet hole. Theradial cracks from a third bullet will terminateinto the radial fractures from the second bul-let, and so forth. The sequence of numerousbullet holes can be determined by thismethod. If the glass is shattered, it may be

necessary to reconstruct the broken piecesfirst. There has been more than one case of ashootout ensuing through the windshield of acar between a police officer and a suspect. Byexamining the termination lines of the radialfractures from each bullet hole and by com-

paring the size of theexit and entranceholes of each bullet,it can be determinedwho fired first.

The directionfrom which a bulletwas fired can bedetermined by com-paring the size of theentrance hole to thatof the exit hole. Exitholes are alwayslarger, regardless ofthe type of materialthrough which a bul-let penetrated.Because glass iselastic and bows

outward when struck by a bullet, a largerpiece of glass will be knocked out on the sur-face where the bullet is leaving as opposed to the very small hole the bullet makes whenit enters.

Because of its elasticity, glass alwaysblows back in the direction the impact origi-nated. Because of the violent tendency ofglass to snap back after being stressed, it canblow back glass several meters in the direc-tion from which the shot originated. If a bulletstrikes a window from the outside and shat-ters it, most of the glass will be on the out-side. This piece of information can beextremely valuable in determining from whichdirection a shot was fired.

Was the light on or off?

Here’s a bit of information that can bevaluable in crime scenes involving a brokenincandescent bulb, especially among vehiclecollisions. It is easy for someone to drive atnight with their lights off while driving down awell-lit street. But suppose you’re cruisingdown the road one night, and bam! You getinto an accident with a motorist who did nothave his lights on. If it could be proven thatthe other motorist failed to turn on his head-lights, this would be a big boost to your case.But suppose it is his word against yours. Byexamining the broken filament of a light bulb,it can easily be determined whether the bulbwas on or off when it was broken.

Light bulbs do not actually burn, butrather, glow as the tungsten filament becomesvery hot due to the resistance that the elec-

http://chemistry.org/education/chemmatters.html

A bullet hole in window glass.

The sequence of shots can be determined: the radial fractures ofthe second hole terminate in those from the first hole.

concentric radialJU

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trons encounter as they pass through the verynarrow wire filament. The definition of incan-descence is the property of emitting light as aresult of being heated, but not actually burn-ing. The electrons in the filament materialabsorb energy and jump to higher atomicorbitals (excited state). They then release aphoton as they fall back to their originalground state orbital. In a properly functioninglight bulb, the glowing filament is inside of thebulb filled with a noble gas such as argon.

But if the filament is glowing when thebulb is broken, it will immediately react withoxygen in the air and break in half. This willform a thick layer of yellowish-white tungstenoxide on the filament due to the reaction ofthe tungsten with oxygen. If the presence oftungsten oxide on the filament is found, thenit can be proven that the bulb was on whenthe accident occurred. The absence of tung-sten oxide on the filament reveals that thebulb was probably off when it was broken.

Solving the crimeSometimes, a bit of deductive reason-

ing is all it takes to solve a crime. In 1988,there were dozens of claims by consumersthat they had found shards of glass in jars ofGerber baby food. After forensic investiga-tors examined these contaminated jars, theydiscovered many different types of glass—glass from mirrors, bulbs, and car head-lights were all found. If the glass came fromthe manufacturing plant due to an accidentsuch as a light bulb breaking over the pro-duction line, then you would expect to findonly one type of glass in the jars, not sev-eral. It was therefore concluded that theglass found in the jars of baby food was aresult of deliberate tampering.

The field of forensic science provides afascinating glimpse into how science can beused to solve crimes. A well-trained forensicscientist uses aspects of biology, chemistry,physics, and mathematics to reconstruct whatmay have happened at a crime scene. Crimi-nals may break society's laws, but they cannotbreak the laws of nature.

Answer to question:The 3.0-g sample of glass has the same

density as the 1.5-g sample. It might be twiceas massive, but then it has twice the volume.Since density is M/V, the density of bothpieces would be identical. Remember, densitydoes not depend on the size of the sample!


REFERENCES Ellis, W. S., Glass. Avon Books: New York, 1998.Fisher, D. Hard Evidence. Dell: New York, 1995.Saferstein, R. Criminalistics: An Introduction to Forensic Science. Pearson Prentice Hall: Upper

Saddle River, NJ, 2004.

INTERNET RESOURCESAutomobile Window Glass—A Design Defect That Should Not Be Overlooked,http://www.auto-law.com/CM/PracticeAreaDescriptions/PracticeAreaDescriptions58.asp.Bullets Out, None In, http://www.discover.com/issues/nov-03/rd/bullets-out-none-in/.Different Types of Glass, http://www.diydata.com/materials/glass/glass.htm.Glass, http://en.wikipedia.org/wiki/Glass.How does safety glass work?, http://computer.howstuffworks.com/questions508.htm.Tempered Glass Breakage, http://alumaxbath.com/tech/tgb.htmWhat makes glass transparent?, http://science.howstuffworks.com/question404.htm.What’s That Stuff? Glass, http://pubs.acs.org/cen/whatstuff/stuff/8147glass.html.

Here is another coolactivity involving glass.

Materialsapproved protective eyewear paper towels(2) 10-mL graduated cylinders1 glass stirring rodglycerol (about 10 mL)water (about 10 mL)

Wear your safety goggles during this activity,and do not taste any of the liquids used.

1. Obtain a glass stirring rod from your teacher.

2. Place about 8 mL of glycerol in a 10-mL graduated cylinder and 8 mL ofwater in another 10-mL graduated cylinder.

3. Put the stirring rod into the graduated cylinder with the water in it.

4. Record your observations.

5. Remove the stirring rod and dry it off with a paper towel.

6. Now place the rod in the graduated cylinder containing the glycerol. Whathappens?

7. Record your observations.

After discussing this activity with your small group, devise an explanationfor what you observed. Be prepared to share this with the class.

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Brian Rohrig teaches at Jonathan Alder High School in Plain City, OH. His most recent ChemMatters article,“The Chemistry of Digital Photography and Printing”, appeared in the February 2006 issue.

Forensic Identification of Glass Activity

As the article on glass points out, it is relatively common to find piecesof broken glass associated with crime scenes. Forensic scientists are oftenasked to determine the origin or prove the identity of various samples ofglass shards.

Finding the Density of Glass:Because the liquids mentioned in the article are not considered safe for

routine high school use, here’s an alternative method that will demonstratethe same concept.

Before you begin, answer these questions:1. If you place small bits of plastic in water, will they float or sink? Will

they float or sink in rubbing alcohol? What information would youneed to know in order to make a prediction?

2. If you used a much larger piece of the same type of plastic, would itaffect whether or not it floats in the liquids?

3. If a piece of plastic sinks in a liquid, what does that mean about thedensity of the plastic relative to the density of the liquid? In terms ofthe density of plastic relative to the density of the liquid, what does itmean if the plastic floats?

Materialsapproved protective eyewear100-mL graduated cylindersmall pieces of plastic from a pen top100-mL beaker10-mL graduated cylinderisopropanol (rubbing alcohol, 70%)waterbalancedropper pipet

Be sure to wear safety goggles while completing this activity.Do not taste any of the liquids used in this activity.

Your teacher will provide you with pieces of plastic that have comefrom ordinary ballpoint pens. Use a balance to determine their mass; recordthe mass as accurately as possible. Place 50.0 mL of isopropanol in a 100-mL beaker. Add water slowly until the plastic pieces begin to rise. Recordthe exact amount of water needed to get the plastic pieces to attain neutralbouyancy; that is, they stay suspended about half way to the top of the liquidmixture.

Using the equation from the article, calculate the density of the plastic.

http://chemistry.org/education/chemmatters.html8 ChemMatters, OCTOBER 2006

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Placing pieces of plastic in isopropanol.

Carefully adding water until the pieces of plastic begin to rise.

At this point, the densities of the plastic and thesolution are the same.


Reduce, Reuse,Recycle!

GreenChemistry

You probably learned that slo-gan in first grade when youcelebrated Earth Day. But

beyond recycling aluminum cansand newspaper lies the building ofan environment-friendly home.Builders across the country are com-peting to design and build greenhomes. Not greenhouses, for grow-ing plants—green homes, meaningenvironmentally responsible homesand construction practices. The ideais to reduce waste in the buildingprocess, create energy-efficient,water-saving homes, and promotethe use of sustainable materials.

Sustainability is a hot buzzwordin the “green” arena, but what does itmean? The U.S. Environmental Pro-tection Agency (EPA) defines sus-tainability as “the ability to achievecontinuing economic prosperitywhile protecting natural systems ofthe planet, providing a high quality oflife for its people.” This calls foreveryone taking responsibility forsolving the problems of today andcaring for the planet for the genera-tions of tomorrow.

The U.S. Green Building Council(USGBC) has created a pilot programcalled LEED, or Leadership in Energyand Environmental Design. The pro-gram is an effort to move the home-

building industrytoward high-perfor-mance, sustainablepractices. Certain crite-ria are used in giving ahome-building projectthe “green building”label, using a commonstandard of measure-ment. For example,homebuilders can earnpoints by these actions,along with others:

• reducing construction waste toless than 2.5 pounds per squarefoot of home;

• reducing energy costs by using efficient appliances;

• building a well-insulated structure;

• installing energy-efficient lighting,heating, and cooling systems;and

• reducing water usage with high-efficiency toilets and natural landscaping.

Homes receiving the highestnumber of points receive a platinumrating, followed by gold, silver, andcertified ratings. The USGBC hopes toincrease consumer awareness of thebenefits of green building, stimulategreen competition, and transform thepractices of the building industry.

ReduceThe residential construction

industry generates 58 million tons ofwaste per year, according to a studyconducted for the EPA. Home reno-vation projects account for 55% ofthe waste, demolition accounts for34%, and new construction accountsfor 11%. Any reduction in theamount of this waste is a step in theright direction.

By Roberta Baxter

Chemistry Builds aGREEN HOME

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One of the biggest costs of homeowner-ship is energy. The chemical company BASFsponsored the construction of a Near-Zero-Energy home in Paterson, NJ. The home wasbuilt with concepts developed by the OakRidge National Laboratory in Oak Ridge, TN,and PATH/Build America, the Partnership forAdvancing Technology in Housing. Thedemonstration home is claimed to be 80%more energy efficient than a typical home. Onsunny days, the home could easily producemore energy than it uses. It is also moredurable, has a lower environmental impact,and is faster to construct than conventionallybuilt homes.

Rather than using wood studs and sidingfor the walls, the Near-Zero-Energy home wasconstructed with foam-insulated concreteforms. These are rigid plastic foam forms thathold concrete in place while it hardens, andthey remain in place afterward to offer extrathermal insulation. The foam insulation keepsheat and cold out of the house by trapping airin the holes of the foam. Air is a very poorconductor of heat, which makes it a goodresistor, impeding the flow of heat. Note thatit's not the plastic foam (or in other cases,fiberglass, stone, wool, or feathers) that slowsthe heat loss, but the air that’s trapped inbetween the layers of an insulating material.

The concrete form technique is quickerthan building a traditional block foundation,and the concrete can be poured and allowedto harden in more extreme climates than nor-mal poured concrete. Concrete is an artificialstonelike material that is made by mixing wetcement, sand, and gravel together. Thecement gradually sets, binding the other com-ponents together to give the rock-like materialyou are familiar with. Using concrete for thestructure eliminates the need to cut downtrees—a green advantage.

A home in New Mexico was chosen asthe VISION House 2006 for Green BuilderMagazine. This is one of over 1 million homesusing a geothermal system to reduce the costof conditioning indoor air. The concept behinda geothermal heating system is to use the heatenergy of the earth to moderate the air tem-perature in our homes: geo (earth) + thermal(heat). Over most of our planet, the top 10feet of the surface stays consistently in the50–60 °F range (10–16 °C). That means thereis a giant, mostly untapped heat and powersource right below our feet.

A geothermal system runs a refrigerantor a water and antifreeze mixture throughpipes buried in the ground below frost depth.

A pump and compressorcirculate the mixturethrough a heatexchanger. In the winter,when the temperatureunderground is warmerthan the surface, thethermal energy of theearth is drawn upthrough the pipes,moved into the home,and is allowed to dis-perse into the rooms.Usually, duct fans dis-tribute the heat through-out the house. Theprocess is reversed inthe summer when theground temperature is

cooler than the surface, helping to cool thehouse. Unwanted heat is concentrated, senton down the line and absorbed by the earth,while cool air is returned.

Geothermal systems are quiet and, com-pact, and they emit no gases so they can beplaced indoors. A side benefit is that they pro-vide inexpensive hot water throughout thesummer. Best of all, the heat source is renew-able—a sustainable system that uses no fossilfuels and emits no greenhouse gases.

In the early 1990s, the U.S. Departmentof Energy contributed significantly to thedevelopment of low-E window coatings. Alsoreferred to as low-emissivity, these windowsuse tin or silver metallic oxides that greatlyreduce the amount of energy needed to heator cool a home. The coatings can be appliedinto the molten glass, sprayed on, or added asa thin film pressed between layers. The win-dows are designed to be solar selective,admitting as much daylight as possible while

blocking transmission of the infrared, or“heat” radiation. Low-E windows are moreinsulating than normal windows because theyreduce radiative heat transfer. They cut downon solar heat gains in the summer and pre-vent loss of interior heat in the winter.

ReuseThe “reuse” part of the slogan also

comes into play in green homes. Contractorsare working hard to reuse pieces of wood anddrywall to cut their costs during new homeconstruction. Several companies reclaim oldwood from demolished houses, buildings, andbarns. Some lumber is even dredged up fromriver bottoms where logs have sunk duringlogging operations. The wood is cut andsanded and fashioned into wood flooring.Using the hardwood from these reclamationssaves trees and reuses wood that would oth-erwise be headed for landfills.

An unusual application is kitchen andbath cabinets made from wheat straw. Thestraw is a waste product from agriculture.Wheat heads are cut off the plant, leaving thestems behind. The chopped straw is gluedtogether with nonformaldehyde containingadhesives and pressed into shape. The cabi-nets look and feel just like wood, and they areproduced from 85% renewable materials.

http://chemistry.org/education/chemmatters.html10 ChemMatters, OCTOBER 2006

Low-E windows are spectra-selective; theyallow selected portions of the solar spectrum topass through while restricting others.

Vision House 2006 in Albuquerque, New Mexico.

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RecycleRecycling is a vital part of any green home.Environment-friendly contractors search formaterials that have been recycled and thosethat can be easily recycled at the end of their use.

One popular product made from recycledmaterials is carpet. About half of the polyestercarpet in the United States ismade from recycled plastics.It takes five two-liter bottlesto make one square foot ofcarpet, so there might be 500recycled bottles on your liv-ing room floor.

Plastics are syntheticpolymers, and polymers arelong chains of repeating mol-ecules linked together (“poly”means many, and “mer”means unit, or part). The typ-ical two-liter bottle is madeof a polymer called polyethyl-ene terephthalate, or PET forshort. You might have seenthis familiar logo on the bot-tom of some plastic prod-uct. PET is a thermoplastic,meaning it can be repeat-edly reheated and reshaped.Once a bottle is used, it canbe recycled by cutting itinto pieces, then cleaningand remelting the pieces. Once it has beenwarmed, the plastic can be either molded tomake new bottles or spun into fibers to makeitems such as carpet and even clothing.

PET is made via a condensation reaction,in which molecules are joined together while amolecule of water is split out.

Another important aspect of the carpetstory is keeping old carpet out of landfills.

Representatives of the carpet industry esti-mate that 3.5 billion pounds of carpetwaste goes to landfills each year. Mostly, it is old carpet that cannot be reused, butindustry giants DuPont and Antron areimplementing carpet-recycling programs. Ifcarpet can be cleaned and reused, it isdonated to charity or sold. If reuse is notpossible, the carpet is recycled into new

plastic products, such asfiltration devices, furniture,and automotive parts.

Another homebuildingmaterial that is often madeof recycled plastic is com-posite lumber. Used fordecks and window anddoor frames, this materialis a 50/50 mixture of woodfibers from sawdust andrecycled plastic. The woodfibers reinforce the plasticlumber, so that it isstronger than 100% recy-cled plastic. Furthermore,the plastic protects thewood from rotting. So the

combination of natural and synthetic materi-als brings out the positive characteristics ofboth wood and plastic.

A huge advantage for the homeowner isthat plastic lumber does not have to bepainted. Color can be added during the man-ufacturing process. As a further blessing tothe environment, composite lumber is madeof plastic and sawdust that would otherwiseend up in a landfill.

Glass winds up in landfills about asoften as plastic, and concrete waste places ahuge burden on landfills. Kitchen counter-tops for the VISION 2006 house were madefrom 75% recycled concrete and glass. Thematerial looks like natural stone.

As homebuildersand the public becomemore aware of the possi-bilities of building greenhomes, more innovativeproducts will come along.Your next home may begreen enough to savethousands of dollars inconstruction and mainte-nance costs. Just thinkwhat you could do withthat green! Roberta Baxter is a science writer who lives in

Colorado Springs, CO. Her most recent ChemMattersarticle, “Battling Zits”, appeared in the April 2005 issue.

Recycling: part of Green Livingincludes sustainability, takingresponsibility for the protection ofour natural resources.

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Many techniques for being greenwere presented to you way back infirst grade or were offered by your par-ents. Here are a few ideas:

1. Turn off lights and electronicswhen not in use.

2. Recycle anything possible: paper,aluminum, glass, and plastic.

3. Close curtains on sunny summerdays and open them on sunny winter days.

4. Buy energy-efficient appliances and electronics when possible.

5. Use appliances wisely; for exam-ple, it’s usually more efficient toheat with a microwave than anoven, and run clothes and dish-washers only when full.

6. Set thermostatsat 68° in win-ter and 72°in sum-mer.

7. Caulkarounddoors and windows.

8. Use fluorescentlight bulbs.

9. Drink tap water rather than bottled water.

10. Use indoor plants like Goldenpothos or English ivy to removeindoor air pollutants.

11. If you are an outdoor gardener,use ladybugs rather than chemi-cal insecticide to get rid of plant-eating insects.

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Ways ToBe Green

The condensation reaction that forms polyethylene terephthalate (PET).PET is a polyester polymer; one of the ester groups is highlighted.


AirPollution

ComesHome

By Michelle Laliberte

How many times have you been toldthis? You might have thought thiswas just a way to get you out of yourparents’ hair for a while. But there

might be some sound chemical reasons tospend some time outside of the house. That’sbecause air pollution can sometimes be a realproblem—inside the home!

All kinds of activities that take placeinside the home can release chemicals or par-ticles into the air. Some are obvious, such asusing an aerosol deodorant or painting aroom. Some are less obvious, like taking ashower, frying food, or rolling on the newplush carpet with your pet dog. In drafty oldbuildings, this was not a big problem, becausethere was enough ventilation to prevent thesesubstances from building up. But to bringfresh air into a building and heat it in the win-ter or cool it in summer costs money. Inresponse to the energy crisis in the 1970s,builders started sealing up homes and officebuildings and air circulation decreased drasti-

cally. With poorer circulation, chemicalsreleased inside the home could build up topotentially dangerous levels. Now, growingpublic awareness of indoor air pollution hasgiven birth to new terms such as “indoor environmental health” (IEH), and “sick build-ing syndrome” (SBS). But news reports maysometimes go too far, sensationalizing thesubject to the point of scaring the daylightsout of us. Should we be worried? What shouldyou do?

Sources of indoor air pollution

Stanley Watras lived in Boyertown, PAand worked at the Limerick Nuclear PowerPlant. During December of 1984, Stanley setoff alarms at the plant as he attempted toenter through portal radiation monitors. Everyday for two weeks Stanley went throughdecontamination while the authorities at thenuclear power plant tried to find the source ofhis radiation contamination. It was confusingbecause the power plant was not yet produc-ing fission products, but the contaminationsource was eventually found.

It was coming from Stanley’s house. AtStanley’s urging, his home was tested for

radiation contamination, and it showed radonlevels 650 times the average level. Radon is anaturally occurring radioactive gas that is abyproduct of decaying uranium and a knowncause of lung cancer. His family, includingsmall children, was immediately evacuated.High radon levels were also found in nearbyhouses. Stanley’s home is on the ReadingProng, a region that stretches from Reading,Pennsylvania through New Jersey and intoNew York. This granite formation has veryhigh deposits of low-grade uranium.

RadonRadon-222 is produced by the natural

disintegration of the radioactive elementradium-226. Radium itself is produced by thedecay of uranium-238, which is found in rocklayers and bedrock. It is present in most ofthe soil and rock around the world, especiallyareas with lots of granite, shale, and phos-phate rock.

With the loss of an alpha particle, radiumis converted to radon gas. Radon itself is notharmful. It is chemically inert (it’s a noble gasafter all) and has a short half-life of only 3.8days. However, Rn-222 undergoes radioactivedecay to form polonium-218, which in turnundergoes decay in a continuing chain termi-

“Why don’t you goplay outside and getsome fresh air?”

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nating in stable Pb-206. These progeny nucleiare charged and chemically reactive, so theyattach to airborne dust particles that can beinhaled into the lung. Several of the progenyare alpha-emitters; when they undergo decay,the energetic alpha particles blast into anddamage the surrounding cells.

Because radon is a gas, it can permeateyour house through the basement or crawlspace or through exposed soil and rockbeneath and around your home’s foundation.Sometimes, it can seep in through well water,or migrate into your home through naturalgas lines.

In order to measure and report anamount of radiation, we need a standard unit;the standard measure for the intensity ofradioactivity of some radioactive substancesis the curie (Ci). The curie is a measure of thenumber of atoms in a collection of atoms thatare giving off radiation per an interval of time.Radium decay is used as the basis for thecurie, and one gram of Ra-226 gives off 2.2trillion decays per minute. A curie is a lot ofradiation, so we routinely speak of radiationintensity in terms of a picocurie. Pico is a prefix meaning one trillionth, or 10-12, so apicocurie (pCi) is equal to 2.2 disintegrationsper minute.

Back to radon—the EPA has set safelimits for indoor radon at 4 picocuries perliter of air (4 pCi/L). The average indoor levelof Ra is 1.3 pCi/L, and about 0.4 pCi/L is nor-mally found in air outdoors. The level ofradon gas in Stanley’s (remember Stanley?)home was an astonishing 415 pCi/L, a levelthat has been estimated to carry a risk equiv-alent to smoking 135 packs of cigarettes perday. In fact, this level of radon far exceedsthat allowed in uranium mines!

Radon gas problems can be corrected(mitigated) by increasing ventilation through-out the house, especially in the basement.Sealing cracks and openings in the foundationcan also help to keep some of the radon out.You can't smell it, so to be safe, all homesshould be tested for radon gas levels; com-mercial test kits are available at many hard-ware stores. So, what happened to StanleyWatras? He and his family eventually movedback into the home after fixing the radon

problem, and now Stanley is successfullyworking in the radon mitigation field!

FormaldehydeFormaldehyde (CH2O) is a volatile and

flammable organic chemical that can bereleased into the air as a pungent, suffocatinggas. It is naturally produced in our bodies invery minute quantities as part of normalmetabolism. We are exposed to formaldehydein the air, food, and in cosmetic products.Known by its other names methanal, methyl-ene oxide, and formalin (a 37% mixture inwater), formaldehyde is one of the top 25most abundantly produced chemicals in theworld. It is used as a disinfectant, preserva-tive, fire retardant in foam insulation, clothing,paper products, carpeting, and—yuck—embalming fluid. Formaldehyde is added tocotton products to givethem wrinkle-resistance,and is added to manymore products, including(believe it or not) Italiancheeses, fish, driedfoods, and toothpaste.

When combinedwith urea or phenol,formaldehyde makes anexcellent adhesive resin,so it is widely used in thebuilding and furnishingsindustry. The construc-tion of pressed-woodproducts such as parti-cleboard often involvesthe use of formaldehyde-based resins. You can

find particleboard all through a home as subflooring and shelving. The formaldehydereacts chemically with urea or phenol to forma resin that binds the materials of particle-board together. Formaldehyde reacts withphenol to form 2,4-dimethylol phenol (A).This compound reacts with 2-methylol phenol(B) in a condensation reaction to form com-pound C. A condensation reaction is onewhere two reactants are joined together as asmall molecule is split out; in this case, thesmall molecule is H2O. Compound C poly-merizes to form the resin known as Bakelite,which sets, or hardens, binding particlestogether.

When the polymer resin forms and thematerial sets, there is not supposed to be anyformaldehyde left; it should have all reacted.The problem comes from small amounts ofunreacted formaldehyde that gets entrappedin the resin and is released over time. Therelease, or outgassing, of the excessformaldehyde is gradual, occurring rapidly atfirst and then slowing over time. Thus, expo-sure is greater in a new home furnished withnew products.

Formaldehyde is a potent eye, upper respiratory and skin irritant. Exposure causescentral nervous system problems, includingheadaches, fatigue, and respiratory depres-sion. It has the potential for inducing asth-matic attacks and recent epidemiologicalstudies of work-exposed individuals suggestthat formaldehyde causes nasal cancer. Tominimize your exposure, buy solid wood furniture when possible, and keep your homeproperly ventilated.


238U ➞ 226Ra ➞ 222Rn92 88 86

Uranium-238 Radium-226 Radon-222

Several decaysteps

Loss of alphaparticle

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Test kits for radon and CO are commerciallyavailable.

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phenol formaldehyde2,4-dimethylol phenol

The formation of a polymer resin used for particleboard. Formaldehyde is akey reagent.

Molds and biologicalpollutants

Molds, mildew, fungi, bacteria and housedust are some of the main biological pollu-tants in the home. Spores generated frommold and mildew are released into the air andform new colonies wherever they land. Areasof the home with high humidity, such as bath-rooms, kitchens, laundry rooms, and base-ments are sources for these living pollutants.Mold can be found growing on paper, textiles,grease, dirt, and even soap scum.

Rather than a single substance, housedust is a varied mixture of potentially aller-genic materials. It may contain fibers from different types of fabrics; cotton lint, feathers,and other padding materials; dander fromcats, dogs, and other animals; bacteria; foodparticles; bits of plants and insects; and otherallergens peculiar to an individual home.

House dust also contains microscopicdust mites. Dust mites feed off of human deadskin cells. They live in bedding, upholstered

furniture, and carpets;thriving in summer andthen dying off in winter.The Mayo Clinic estimatesthe average bed containsbetween 100,000 and 10million dust mites. You maybe sharing your bed with mil-lions of them! The particles seenfloating about in a shaft of sunlight includedead dust mites and their waste products.Dust mites have been identified as the singlemost important trigger for asthma attacks.Asthma, a chronic ailment that afflicts millionsaround the world, causes inflammation of theairways and affects the way air enters andleaves the lungs, thereby disrupting breathing.

You can pinpoint these triggers of indoorallergens in your home by visual detection.

Keeping mold growth under control is accom-plished by making sure basements, bath-rooms, and other rooms are clean and dry.Chlorine bleach will remove any visual moldand can be used to clean out humidifiers andair-conditioning condensing units. Use vacu-ums with high-efficiency filters and considerreplacing old carpet with hard surface flooringif anyone in your home is sensitive to theseallergens. Wash sheets, pillowcases, and blan-kets weekly. This removes dust mites’ primarysource of food—your dead skin cells.

Carbon monoxideAccording to the Journal of the American

Medical Association, 1,500 Americans dieeach year from accidental exposure to CO, andover 2,000 from intentional exposure (sui-cide). Carbon monoxide is an extremely haz-ardous gas that has no warning taste or odor.It is produced by incomplete combustion oforganic fuels such as wood, gasoline, naturalgas, coal, charcoal, and fuel oil. Like oxygen,carbon monoxide binds to the iron atoms ofthe hemoglobin (Hb) protein molecules foundin our red blood cells, forming a complexcalled carboxyhemoglobin. Carbon monoxidebinds to hemoglobin about 200 times morestrongly than does oxygen. It was longbelieved that because carboxyhemoglobin isunable to transport oxygen, fatal carbonmonoxide poisoning is due to asphyxiation.This sounds bad enough, but a detailed exam-ination of carbon monoxide poisoning revealsa more complicated, more insidious situation.

Hemoglobin is a tetramer, that is, eachhemoglobin protein has the ability to

bind to four oxygen molecules. Itsoxygen binding exhibits a phe-nomenon called cooperativity:once the first oxygen moleculebinds, the protein changes itsshape in such a way that the

remaining three sites bind oxygenmore tightly. This is physiologically

important, making Hb better at bindingO2 in the oxygen-rich lungs and better atreleasing O2 in the oxygen-poor muscles.However, the CO-bonded iron looks (as far asthe protein is concerned) a lot like the O2-bonded iron. So the Hb shifts into high-affinitymode when even one CO is bound per proteinmolecule. This means that it picks up the O2

well in the lungs but cannot release it in the tissues! A person suffering from exposure tocarbon monoxide actually has high oxygenblood content. It’s just that the oxygen cannot

be released where it is needed: the brain,heart, and skeletal muscle. For more informa-tion on this topic, see Tim Graham’s article“The Silent Killer” in the February 2005 issueof ChemMatters.

Carbon monoxide buildup occurs whenflues or chimneys become blocked andexhaust cannot be vented outside. Faulty fur-naces, fuel-burning space heaters, ovens,ranges, and even grills operated in the homewithout adequate ventilation will also causecarbon monoxide buildup. To prevent thisexposure, carbon monoxide alarms and detec-tors are available in stores and should beinstalled to alert you of dangerous levels. Alsomake sure you have your combustion heatingsystems and chimneys checked by trainedprofessionals every year.

Safe havenEven though we have only listed several

of the many toxic indoor air contaminants, thesubject can be frightening. Our homes shouldbe a safe haven, not a hazardous waste dump.Every time you get dizzy, have a sore throat,or have itching, burning eyes will you wonderif it has to do with the air quality of the room?Education is the key to keeping your indoor airclean and healthy. Remember, it’s not just theoutside air we have to be concerned with any-more. A little forethought and action can go along way in preventing major health problemsarising from contamination occurring in yourown home.

Michelle Laliberte is a science writer living inMedina, OH. This is her first article forChemMatters.


Dude—do you have any idea what’scrawling all over your pillow?

A barbeque grill is an example of a CO-producingdevice. Never use a grill indoors.

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WWW.ARS.USDA.GOV


The New Alchemy

ChemHistory

By Michael McClure

n 1927, Georges Lemaitre, aBelgian priest, proposed thatthe universe began with a cos-mic explosion of gigantic pro-portion. He suggested thatbefore the explosion, there was

a time when all of the matter andenergy of the universe were packedtogether into one fantastically denseand unstable mass that he calledthe cosmic egg. A few minutes afterthe violent blast, protons and neu-trons joined to create simple atomicnuclei. Some time later, electronsbegan interacting with the nucleiand atoms of the simplest ele-ments, hydrogen and helium, wereformed. As the rapidly expandinguniverse cooled, great clumps ofgas condensed, heated up, andexploded in a burst of light. Thefirst stars were born.

The stars were the crucibles inwhich nuclei were fused to formheavier elements. A star’s energycomes from the fusion of nuclei asmass is converted to energy,according to Einstein’s famousequation E = mc2. Carbon, oxygen,neon, and all of the elements up toand including iron are synthesizedduring the life cycle of a star. Ele-ments beyond iron are made whenmassive stars end their lives assupernovae. The nuclear reactionsthat produce elements beyond ironrequire more energy than they pro-

duce, so these elements will notform under the conditions of a nor-mal star. But the enormous energyavailable in an exploding supernovais sufficient to drive nuclei and otherparticles together. As nuclei areforced to absorb protons and neu-trons, they can grow to form ele-ments with masses greater than thatof iron, and they can continue togrow, forming elements as heavy asuranium.

The early years:Who were theplayers?

Billions of years later after thatinitial, tremendous blast, scientistsin the 19th and 20th centurieswould organize all of the known ele-ments into neat rows and columnsbased on properties and atomiccomposition—the Periodic Table. Inthose early years, discoveries camefast and furious. It was predictedthat new discoveries might one dayreveal elements with masses andatomic numbers beyond uranium.What were these discoveries? Whowere the men and women thatunlocked the secrets of atoms andcreated the first transuranium (i.e.,“beyond uranium”) elements? Whosucceeded in doing what earlyalchemists failed at—transformingone element into another?

Before we dive into these dis-coveries, let’s first take a look at thebasics of radioactivity.

RadioactivityRadioactivity refers to sponta-

neous nuclear reactions that occurin various forms. Atoms that decayby alpha emission, for example,eject a particle consisting of 2 pro-tons and 2 neutrons, in other words,a helium 2+ ion. The decay product,or daughter, is an element with twofewer atomic number units. Forexample, the isotope uranium-238decays into thorium-234 by alphaemission.

Other modes of radioactivedecay include beta decay, positronemission, and electron capture.

Radioactivity can be used as atool for exploring the atomicnucleus. In 1919, the New Zealand-born physicist Ernest Rutherfordobserved the reaction between alphaparticles and gaseous nitrogenatoms in a cloud chamber. The cloudchamber is a flask filled with super-saturated vapor, in this case, nitro-gen gas. Alpha particles streakingthrough the vapor knocked electronsfrom nitrogen molecules, creatingelectrically charged ions. Vapor mol-

238U ➞ 234Th + 4He92 90 2

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ecules condensed around the ions, allowingRutherford to see the alpha particle path as atrail of tiny droplets, like the contrails of a jetaircraft.

Rutherford recorded the short tracks ofmany alpha particles in his experiment. Occa-sionally, he observed condensation tracksthat were longer than expected. Becauselonger tracks implied less massive particles,Rutherford suggested that perhaps alpha particles were knocking out protons from thenucleus of nitrogen atoms. Gaining two pro-tons, then losing one proton would changethe nitrogen nucleus into oxygen-17. Ruther-ford had just observed the first artificial trans-mutation of an element.

Transmutation is the transformation ofone element into another through one or aseries of nuclear reactions

An artificial isotopeLater on in 1934, Irene Curie-Joliot, the

daughter of Marie and Pierre Curie, and herhusband Fredrick Joliot performed an experi-ment similar to Rutherfords’. Instead of nitro-gen, they used aluminum as the target. Inaddition to protons flying away from the colli-sion event, they observed the emission ofneutrons and some new form of radiation(called a positron emission). Surprisingly,when they stopped the experiment, neutronemission stopped, but the radiation contin-ued. How could this be? Curie-Joliot and herhusband discovered that the reaction createdthe artificial element phosphorus-30. Thisisotope does not occur in nature, and itdecayed into silicon by this newly discoveredform of radiation—positron emission. Theyhad witnessed the first artificial transmutationof a stable element into a radioactive isotope,by emission of an artificial form of radiation.In 1935, the Curie-Joliot’s shared a NobelPrize for this work.

Building new atomsand a stunning discovery

Early alchemists worked furiously tryingto change one element into another, and theyall came to the same conclusion: it’s not easy.What they did not know is that positivelycharged protons inside the nucleus of everyatom repel similarlycharged particles. Thecharacters of our storyfound that only posi-tively charged particleswith sufficient energycan overcome thestrong repulsive forcesand penetrate thenucleus. For this rea-son, Enrico Fermi, anItalian physicist, sug-gested that neutronsmight make betternuclear missiles. Neu-trons carry no electri-cal charge; they areneutral. Fermi and others believed that if anucleus captured a neutron, it would try tocorrect for its neutron excess by beta decay,turning a neutron into a proton, thus creatingan atom with an atomic number increased byone unit. Suppose uranium, the heaviestknown naturally occurring element, could beforced to capture a neutron. This might makethe uranium nucleus unstable and radioactive.If the unstable nucleus decayed by beta emis-sion, a new element beyond uranium wouldbe created.

Fermi and his collaborators bombardeduranium-238 (atomic number 92) atoms with

slow neutrons. Other research groups wereperforming similar experiments. Initially,everyone claimed success in creating a newelement with atomic number 93. But the massof the product did not agree with the expectedmass of element 93. Furthermore, its chemi-cal properties seemed surprisingly like bar-ium, an element much lighter than uranium.Lise Meitner, an Austrian physicist, was trou-bled by these findings. Looking closely at theresults and making detailed calculations shecame to the astonishing conclusion that uranium nuclei were splitting into smallerfragments! In seeking new elements beyonduranium, Fermi and others had stumbled uponthe process of atomic fission. This discoveryand the subsequent development of nuclearweapons and nuclear reactors impacted all ofhumanity.

Today, we know that Fermi’s uraniumsample contained trace amounts of uranium-235, a rare isotope that undergoes atomic fis-sion when bombarded with neutrons. WhatFermi and others did not realize was that ele-ment 93 had actually formed in the experiment,but was undetectable in the complex mixture.

A planetary elementThe emission of alpha particles creates a

recoil effect. This causes the product isotopesto fly away from each other and deposit somedistance from where the decay eventoccurred. American physicist Edwin McMillanin the Radiation Laboratory at the Universityof California, Berkeley, wanted to know exactlyhow far the fission products would travelthrough matter. His experiment was simple.First, he stacked thin sheets of paper togetherto form a small book. On the top sheet heplaced a sample of uranium salt. Next, he

14N + 4He ➞ 17O + 1H7 2 8 1

27Al + 4He ➞ 30P + 1n13 2 15 0

30P ➞ 30Si + 0e15 14 +1

Transmutation is the transformationof one element into

another through one or a series ofnuclear reactions

The process of nuclear fission.

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exposed the salt to a source of neutrons,which induced fission. As expected, the fis-sion fragments traveled through the papersheets stopping at various layers in the book.McMillan could determine the location of eachfission product by separating the pages andmeasuring the radioactivity with a Geigercounter. But in addition to finding various fis-sion products scattered among the pages,McMillan detected two separate beta activitiesin the topmost sheet. Two isotopes were notrecoiling with the other fission fragments.

McMillan reasoned that perhaps not allisotopes of uranium undergo fission. Maybeuranium-238 was indeed capturing a neutron,as Fermi had suspected, and decaying into anew element. In 1940, Philip Abelson, anotherAmerican physicist from the Carnegie Institu-tion in Washington, went to Berkeley to helpMcMillan identify the mysterious beta activi-ties. Soon they had successfully separatedand identified the first transuranium element.They named the element neptunium (Np).

Why name #93 neptunium? First take aguess, and then look to the end of the articlefor the answer.

The search went on…McMillan suggested that the second

short-lived beta decay product in the mixturemight be an element with atomic number 94.The American scientists Glenn Seaborg,Arthur Wahl, and Joseph Kennedy wereworking on the WorldWar II Manhattan Pro-ject with McMillan anddecided to test hisidea. First, they had toovercome two difficultproblems. In McMil-lan’s experiment,only small amounts

of uranium-239 and neptunium were formed.And the long half-life of the unknown isotopemade it difficult to measure its activity.Seaborg’s group knew they would need tosynthesize larger quantities of neptunium ifthey were to be successful in identifying themysterious product. They solved these prob-lems with the help of (American physicist)Ernest Lawrence’s proton merry-go-round—the cyclotron. Lawrence’s cyclotron couldaccelerate particles to enormous speeds,imparting enough energy to overcome therepulsive forces inside an atomic nucleus.Using the cyclotron, they produced largequantities of neptunium and then watched asthe neptunium decayed into an element withatomic number 94. Seaborg’s group was ableto show that element 94 was radioactive, emitting alpha particles with a half-life of 90 years. After the tradition of naming ele-ments for the planets, element 94 was namedplutonium.

McMillan moved on to other projects, but

between 1944 and 1974, Seaborg’s group dis-covered nine additional transuranium ele-ments. A few were synthesized in ever largerand more powerful cyclotrons, and some innuclear reactors. Two new elements, ein-steinium and fermium, were discovered in thenuclear fallout during thermonuclear weaponstesting in the 1950s.

Revamping the periodic table

Where did the transuranium elements fitinto the Periodic Table? Scientists soonlearned that many transuranium elements had

properties similar to the transition metals. In1944, Seaborg proposed his Actinide hypoth-esis. He predicted that thorium, protactinium,uranium, and the first 11 transuranium ele-ments would form a series of chemically similar elements following actinium (atomicnumber 89), similar to how the lanthanidesfollow lanthanum. Much research into thechemical properties of the transuranium ele-ments has confirmed Seaborg’s hypothesis.

The search continues …

Today, 111 elements are listed in thePeriodic Table. There are 19 transuranium ele-ments named after planets, countries of dis-covery, and scientists. And elements beyondatomic number 111 have been reported butremain unconfirmed and unnamed. Will therebe an end to the discovery of transuraniumelements? Will scientists reach the hypothe-sized “Island of Stability” where theory pre-dicts elements with atomic numbers as highas 126 may be stable? No one knows theanswers. But we do know the search will con-tinue, and perhaps you might be involved.Larger accelerators will be built to smashatoms. New detectors will allow researchersto track and interpret the zoo of particles thatform when atoms collide. And each new dis-covery will increase our understanding of theworld around us, including you and me!

Mike McClure worked for several years as achemist at a veterinary diagnostic laboratory, inves-tigating unusual animal deaths. He now teacheschemistry at Hopkinsville Community College inKentucky and is a regular contributor toChemMatters magazine.


Seven-kilometer–long accelerator in French andSwiss country side near Geneva.

CERN

238U + 1n ➞ 239U92 0 92

239U ➞ 239Np + 0e92 93 +1

Glenn Seaborg

GETT

Y IM

AGES

C&EN

So, you’ve been out of high school for a few years and are enjoy-ing your first job at a manufacturing plant. As manager in

charge of production, you have many job functions, not theleast of which is dealing with safety. Employees haveordered some new supplies, and one of your tasks isto review the Material Safety Data Sheets (MSDS) foreach of the products. As you review the sheets look-ing for hazards, you notice some alarming informa-tion. For substance #1, the section on first-aid

measures advises if it is taken internally,large quantities of water should

be given and a physi-cian or poison

control should be called at once. For substance #2, the fire-fightinginstruction states, “Use triclass dry chemical fire extinguisher. Fire-fighters should “wear personal protective equipment (PPE) and self-contained breathing apparatus (SCBA) with full face piece, operated inpositive pressure mode.” The MSDS advises for substance #3, that

one should avoid contact with eyes, skin, and clothing. Wear chem-ical splash goggles, chemical-resistant gloves, and chemical-

resistant aprons.Pretty scary. And what are these scary substances?

Substance #1 is baking soda.Substance #2 is beeswax.Substance #3 is cotton.Scary indeed.Most students will recog-

nize baking soda as a commonkitchen ingredient, used for making

cookies and cakes. Far from beingconsidered a poison, it is often used as medicine for upset

stomachs when taken as “bicarbonate of soda”. Baking sodais the common name for sodium bicarbonate (NaHCO3),which is a weak base. Because it is a base, it can be used toneutralize excess acid in your stomach.


By Michael Tinnesand

NaHCO3 (s) + HCI (aq) ➞ NaCl (aq) + H2O (I) + CO2 (g)

Material Safety Data Sheets:

ACS

STAF

F


Beeswax is a natural substance pro-duced by honeybees. A mixture of long-chainhydrocarbons and esters, there is no simplechemical formula, but the molecules makingup this type of wax will typically have between20 and 40 carbon atoms. Beeswax is used inmaking wood polish and candles. The con-ventional method of extinguishing the flameof a beeswax candle is with a slight puff ofair, usually from someone’s mouth. Cotton isone of the oldest andmost widely used textilefibers in human history.It is used for all kinds ofclothing, notably forunderwear, where it isworn next to the skin,generally withoutresorting to goggles or aprons.

What exactly are these Material SafetyData Sheets and why do they seem intent onscaring us out of using substances we knowto be safe?

MSDSs are a very important part ofsafety precautions mandated by the Federalgovernment some 25 years ago. Before thattime, workers were on their own to discoverthe potential hazards of chemicals used in theworkplace. To make matters worse, many ofthe products they were using were listed onlyby their brand or trade names, often without alist of ingredients.This made it nearlyimpossible to findout what the hazards might be. In 1986, theOccupational Safety & Health Administration(OSHA) established the Hazard Communica-tion Standard. The standard requires that

• Chemical manufacturers and importersmust evaluate the hazards of the chemi-cals they produce or import, and preparelabels and MSDSs to convey the hazardinformation to their customers.

• All employers with hazardous chemicalsin their workplaces must have labels andMSDSs for their exposed workers andtrain them to handle the chemicals safely.Although the Hazard Communication

Standard does not apply to state and localgovernment, most states have enacted similarlegislation or have endorsed the OSHA stan-dards. Therefore, public and private schoolsmust pay attention to MSDSs as well. As aresult, many high school chemistry teachersreceive instruction on how to read a MSDS aspart of their general safety training for work inthe laboratory.

But in order for an MSDS to be helpful,they must be accurate. That means beingconsistent and reasonable in stating the hazards associated with the materials inquestion.

A recent article by Stephen Ritter inChemical & Engineering News highlightedsome of the issues. The article cites an exam-ple of a MSDS for deionized water, hardly hazardous by most standards, but a common

item for use in research and academic labs.Information on the MSDS included the solubil-ity of water in water, a recommendation towear gloves when dealing with it, and storingit in a cool, dry place! When getting deionizedwater in the eyes, one sheet recommended“irrigate with water”.

To be fair, it is important to note that thevast majority of MSDSs are probably accurateand helpful, but users are well advised not torely on them without cross-checking.

The American Chemical Society Commit-tee on Chemical Safety publishes ChemicalSafety for Teachers and Their Supervisors,Grades 7–12. It notes, “Usually, MSDSs arenot written for the laypersons: they requireinterpretation by persons familiar with thetechnical terms used. Often, an overemphasisis placed on the toxic characteristics of thesubject chemical. There may also be vague orinsufficient information regarding other haz-ards that the subject chemical presents.”

So, how is it that so many MSDSs areinaccurate or inappropriate? The primaryreason is that there is no one to check thequality of MSDS content. After passing thelegislation creating the MSDS, OSHApromptly excused itself from enforcing anylevel of quality in the sheets, instead leavingit to the manufacturers themselves to assessthe hazards and write high-quality MSDSs.As Chemical Safety for Teachers and TheirSupervisors puts it, “Generally speaking,MSDSs from well-known, established sup-pliers of laboratory chemicals are likely to bebetter and more reliable than MSDSs fromother sources. Often, a comparison ofMSDSs for the same chemical from a varietyof suppliers will suggest a source of MSDSsthat is likely to be the most authoritative.”

OSHA recently responded to these con-cerns with a study of the Hazard Communica-tion Standards. The report, HazardCommunication in the 21st Century Work-place was published in March 2004. It makesa number of recommendations, including anew short course to train those who write theMSDSs and a checklist to help review the content of the MSDS.

Perhaps, most importantly, OSHA staffwill begin to critically review the MSDS for 10chemicals, working with manufacturers tomake certain they are accurate and reasonable.

So, perhaps things will get better. In themeantime, consult your teacher if you have

any concernsabout chemi-cals in the lab.And you mightwant to bemindful of youroutdoor activi-ties, especiallywhen it comesto dealing withsand. If you follow the

advice from one MSDS and avoid making contact with your skin or clothing, it is goingto put a real damper on your time at thebeach!

Michael Tinnesand is the Associate Director ofAcademic Programs at ACS. His most recent arti-cle, “The Dog Ate My Homework and Other Gut-Wrenching Tales”, appeared in the April 2006 issueof ChemMatters.

JUPI

TERI

MAG

ES

When working with chemicals, be aware of thehazards involved. Know where the MSDSs arekept and how to interpret them.

MIK

E CI

ESIE

LSKI

1155 Sixteenth Street, NWWashington, DC 20036-4800

Reach Us on the Web at chemistry.org/education/chemmatters.html

A publication of the Education Division of the American Chemical Society

As part of the National Chemistry Week 2006 celebration and in recognition of its theme, "Your Home—It’s All Built on Chemistry", theAmerican Chemical Society (ACS) is sponsoring a poster contest for high school students.

Students are invited to create a poster that will serve as a public serviceannouncement emphasizing the role of science/chemistry in the home.

Prizes!1st Place: $200 Gift Certificate to amazon.com2nd Place: $100 Gift Certificate to amazon.comThere are also prizes for other categories (K-8),

and for the teachers of winning students.

For important information about the contest, go to chemistry.org/ncw, orcontact the American Chemical Society, Office of Community Activitiesat 800-227-5558, ext. 6097 or e-mail [email protected].

National Chemistry Week October 22–28, 2006

National Chemistry Week 2006Poster Contest

“ Your Home—It’s All Built on Chemistry ”

YOUR HOME—It’s All Builton Chemistry

Also Inside:Chemistry Builds

a Green Home

®OCTOBER 2006

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