Wichita State University Wichita. KS 67208
Dozen, Gross, Nerds, Moles, and Sons Allon J. Banks Southwest Texas State University San Marcos, TX 78666 If you have had the opportunity to teach general chemistry a t least once then you have most likely seen a haze form over some of your student's eyes as you talk about moles. During the past two semesters I have used a technique for demonstrating the mole concept that seems to work effectively for my students. I beein - mv.discussion of matter bv discussine.- atoms and molecules-a common approach, to say the least. Inevitably this discussion includes the minuscule proportions attrihut. . ahle to m e atom or one molerule of a ;uhrtanw. I'resenting the "rohlwn of working with only one atom or molentle. I attempt to elicit from students the convenience of using several atoms or molecules. Almost invariably the next question to arise is "How many should we use?" A dozen is a common answer. Pointing out that only 12 objects of atomic dimensions are still of an awkward size.. I sueeest -- the utilitv of larger "counting units". Invariably someone suggests a gross. At this point I usually display 144 objects of uniform size, reminding them once again of the minuscule proportions of atoms and molecules. Next stop-Avoaadra's number! The haze descends as students wrestle wiih the magnitude of that imposing number. I t seemed to me that providing an intermediate "counting unit" might help this transition for the students. Enter my son, Jonathan.. .. While shopping with me one afternoon, my son requested that I buy some Nerds. After the initial shock of learning that this word referred to a type of candy (copyright 1984, Willy Wonka Brands), I discovered that these very small candies are sold in containers resembling. a t least in mv mind, an oddly shaped frog (see figure). ~ f f k inspecting r thk size of these candies, I inveigled my son to count the candies contained in several of the frog-shaped containers. When promised that he could eventually eat all the candies in the several packages I purchased, he eagerly began counting candv. In each of the four containers of Nerds, he counted apprbximately 620 candies. I was now ready to propose an intermediate counting unit!
Armed with several of the plastic creations filled with the tiny candies, I began my lecture on moles, but I didn't talk countine unit of about moles. I introduced the "Nerd"-a 620 things. Following the initial twittering over theunusual name. we discussed the mass of one nerd of X and proceeded to use a nerd of molecules of X in a typical dikussion of reaction stoichiometrv. The plastic containers fit nicely on the stage of an overhead proiector, making i t easy to "ise a nerd of X" in a reaction that had been written on the screen. The extrapolation to a counting unit of Avogadro's numher seemed much easier following .this foray into "unusual units". There is a lack of uniformity in the masses of these candies, providing the lecturer an opportunity to discuss the subject of isotopes-albeit to a limited extent.
my
A nerd container.
956
Journal of Chemical Education
"Million" Ideas Avogardro's number is so large that many teachers of beginning chemistry students use the concept of the size of a million as a steppingstone to the visualization of a mole.
The Mllllon Actlvlty Clark J. Godshall (Penn Yan Central Schools, Penn Yan, NY). The need to conceptualize large quantities such as a million is important to the study of matter, mass, molarity, atomic weiahts, and measurement. Help students visu. your . alize the quantity of a million by preparing a single sheet of 8% x ll-in. paper with asterisks (*) on your word processor. (You can also do this on a typewriter with a little additional work.) Approximately 1,350 can be typed on a page. Make enough duplicate copies of the page to acquire one million dots. It will take 741 of the sheets described above. Tape the pages on a large classroom or hallway wall to display the million dots in an impressive and memorable way. If you remove the copies carefully they can he saved for another year to save duplicating costs. J i l l Herrick (Middleburg Heights School, Cleveland, OH) had her students collect one million bottle caps in a large bin with transparent sides t o help them see how large a million really is. Kevin vander Water, a student a t Downers Grove South Hiph School. Na~orville. . IL.. wrote a microcom~utersoftware pnyrsm that stacks paper from earth LO Pinto, unly to iind that it taker six million of these hridaes to mitke a mole. This program is available from the project SERAPHIM, Eastern Michigan University, Ypsilanti, MI, 48197. The editor's advanced chemistry students decided to make one million paper punches. I t was a t 250,000 that they decided that they would graduate before reaching one million. They thus reached an appreciation of the size of the quantity.
