DOUGLAS D. SMITH
Avogadro's Number One of the conceDts in hiih school chemistw that is initiallv difficult for students to understand is ~vogadro'snumber. Recentlv. when involved in this struggle -- a new a.~.p r o a c h(to me, at least) was discovered. Since most of the students had little previous knowledge of atomic structure, they needed the fundamentals explained: (1) that the atoms of elements are made up and - of protons neutrons in the nucleus, (2) the nucleus is surrounded by a rapidly moving cloud of electrons of equal and opposite charge to the protons in the nucleus, (3) neutrons have no charge, and the atomic mass is concentrated in the nucleus with protons and neutrons heine of about eoual mass-1.66 X 10-24 e. For convenience, 1.66 X 10-24 g is called one atomic mass unit (emu). Thus the masses of atoms can be expressed in amu which would roughly represent the sum of thk protons plus neutrons in the nucleus. In order to have quantities that are manageable in chemistry laboratories, it is necessary to deal with amounts of material that can be seen and measured. For elements, a convenient hulk amount is the gram atomic weight or gram atomic mass (G.A.M.). This is the number of grams of the element numerically the same as its atomic mass in amu. (For example, the atomic mass of gold is 196.97 amu; therefore, 196.97 grams of gold is one G.A.M.) If we take one G.A.M. of
any element and divide i t by the mass of the average atom of the element, we will get the number of atoms present in one G.A.M. This number of atoms, 6.02 X 1023,we call Avogadro's numher. In other words, when we have a G.A.M. of any element we have 6.02 X loz3atoms. Students have always remained skeptical as various calculations were tried to convince them that one G.A.M. of any element contains the same number of atoms as a G.A.M. of any other element. A solution occurred when a student suggested that the problem be set up as follow atomslg Cs 'latom~s 1amu 132.9 amu 1.66 X 10-24g gCs1G.A.M. r atoms x - 132'9g Cs = 6.02 X 10231 G.A.M. G.A.M. Since the 132.9 (or the atomic mass of any other element) will always divide out, it becomes quite clear that this number must be the same for all elements,
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Kenneth L. Retherford Warren Central High School Indianapolis, I N 46229
New Element? Puns, gag definitions, cartoons, and jokes are among the items teachers use in order to change the pace of their instruction. Here is an example from the P a s t w e r e they male chauvinists or just preoccupied in 1925.' A New Element = Woman
Symhol-Wo A member of the Human familv. O r c u r r e n w ('an hs found whrrevrr man exists. Seldum occurs in the free or native state. ()unlity depends un the atate in whwh it is state found. With the erceptm of Maszachusertsslate, t h omh~ned ~ is to he preferred. Physical Properties: All colors and sizes. Always appears in disguised condition. Surface of face seldom unprotected by coating of paint or film of powder (composition immaterial). Boils at nothing
and may freeze at any moment. However, it melts when properly treated. Very hitter if not used correctly. Chemical Properties: Extremely active. Possesses a great affinity for gold, silver, platinum, and precious stones of all kinds. Violent reaction when left alone by men. Ability to absorb all sorts of expensive food at anti time. Undissolved bv. liauids. . . but activitv. is ereatlv .. . inrreau~dwhen saturated with spirit solutionr. Sometrmes yields to pressure. Tumn green when plavtd neat to a brrter appearing sample. Ages wry rapidly. Fresh variety has great magnetic artractiun. Note: Hiehlv and likelytn be dangerous in inexperienced - .exnloaive . bands. (Letters will not be replied to without self-addressed enuelopes.) 1 J. CHEM. EDUC., 2,1044
(1925)
Lead Poisoning and the Fall of Rome Lecture Notes: or Students Remember the Illustration Longer Than the Principle Gilfillanl reasons that lead poisoning was a major reason For the fall of Rome. His areuments. reasonine. -. information and conclusions fit into many discussions or lectures as interestine illustrations. A maior mint is that there was no direct observ&le connection between the means of building up of 334 1 Journal of Chemical Education
lead in the body and resulting complications that developed over a period of years. We may currently be getting a quarter of the 1mg daily that mav he daneerous. Fortunatelv. .. we can secrete this amount, but a larger amount results in a buildup in our bodies espen t - while in the ciallv in the hones. Lead does no a .~.~ a r edamage bones but may cause poisoning when an excess occurs or an
acid condition arises i n t h e body (alcoholic excess or illness). I. Conclusions: 1) A major factor in the fall of Rome was the slow, self-poisoning with lead. 2) Lead poisoning affected only the wealthy, who became disabled and almost childless, (thus leaving more responsibility to less educated). 11. Why wealthy and not the poor? 1) Chief sources oflead were found in foods which were not as plentiful to the poor (wine, olive oil, grape syrup, honey, preserved fruits). 2) Lead pipes (which were not very plentiful in the rural areas) were used to store and transnort water. 3) Well-to-doused lead or lead lined pots. A ) Roman pottery was weak, ponm, and a poor ronductor of heat. B) Copper pots turned green when used with acid fwds while lead did not. C) Food left in copper containers tasted had and brought on sickness while lead produced salts that are light colored, tasteless or sweet, and produced no immediate comnlieations. D) Lead wnseawer to work wth and cheaper thanother known metals of s~lver,tm, gold, mercury, and iron. 4) Cosmetics were used only by the wealthy. Galena was used for black eyebrow paint and ceruse (PbC03) as a face ~
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powder. (Inhalation is 10-100 worse than swallowing). Physicians used lead based salts in some medicines. The poor did not have access to physicians. 111. Reactivity of lead resulted when 1) lead salts were oroduced with acid foods in lead containem. 2) heating containers increased lead's chemical activity. 3) lead found its way into wine and grape syrups. A) Wine was warmed on cold days hefore drinking. B) Grape syrup was made by boiling down grape juice to be used a) as sweetener. b) to preserve fruits and grapes as lead poisons micro-organisms that caused fermentation and souring. c) when grape syrup was too sour and lead oxide wa. arlrlpd -. --. -.
IV. Evidence 1) In 1906 skeleton remains from the ancient world were analyzed end four from Roman Carthage showed lead while the other 18remains (which were found outside the Roman Empire) showed no lead poisoning. 2) An exoeriment where a lead nlate was used in a container wher;grape juice was boiledto half 1q1. volume produced enmgh lead cvntent to do severe damage if only one tsblespoon aday wasconsumed over an ~xtendedparind of time. ~
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Gilfillan, S. C., Mankind Quarterly, 5,131, (1965)
More on Lead C h e m 13 N e w s ' reports that lead poisoning is still a major area of concern. In the United States 201) children still die of lead poison~ngwhile 12,000 t t ~16,000 are treaced and survlve. At Ira51 one-fourth of tho.? treated suffer Dermanent i n w -a.
T h e greatest cause of lead poisoning is t h e eating of leadbased paint by children. T h e second most common source is illicit liquor (moonshine) t h a t is m a d e from makeshift distil-
lation equipment. Even if persons are shielded from the abov6 sources, lead is present in cigarettes, drinking water, f w d , anc air. Evidence has been building on the increased concentratior of lead in people living near freeways, presumably d u e t o tht lead from leaded gasolines.
Donaldson, et al., Chem 13News, 92,1, (1978).
Volume 55, Number 5, May 1978 1 335
