Understanding the particulate nature of matter - ACS Publications

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Understanding the Particulate Nature of Matter Dorothy L. Gabel and K. V. Samuel Indiana University, Bloomington, IN 47405 Diana Hunn lndiana University at Kokomo, Kokomo, IN 46902 Recent studies of students' conceptual knowledge of chemistry indicate that students do not understand some of the fundamental ideas that form the basis of the discipline. Misconce~tionsabout physical and chemical changes on the three leveis that chemistduse to describe chemical phenomena are common. On the macroscopic level, Osborne and Cosgrove (I) in a study on the changes of states of water found that 25% of their sample of 17-year-old chemistry students thought that the bubbles in boiling water were who examined stumade of air. Shepherd and Renner (3, dent's perceptin& of the states of matter on the microscopic level, found none of the high school students in their sample had a sound understanding of the particulate nature of gases, liquids, and solids, and that only 43% had a partial understanding. This lack of understanding of the particulate nature of matter is confirmed by Novick and Nusshaum (3) who found that although misconceptions diminish with schooling, they still persist in university students. They found that among students in the university and in high school, 50%did not attribute the uniformity of particle distribution in gases to inherent particle motion, and over 60% did not space in a gaseous medium. In addition to the prevalence of misconceptions on the macroscopic and microscopic levels, students do not understand the meaning of the symbols chemists use to represent the macroscopic and microscopic levels. Eylon, Ben-Zvi, and Silherstein (4) found that when given a chemical formula for a relatively simple molecule, 35%of the high school chemistry students were unable to represent i t correctly using circles representing atoms. These students had an additive view of chemical reactions rather than an interactive one. Ben-zvi.. Evlon. and Silherstein (5) also found that many . students perceive a chemical formula as representing one unit of a substance rather than a collection of molecules. Of those that did perceive the formula as representing a number of particles in a solid, only two-thirds drew the particles in an ordered fashion. Students are able to use formulas in equations and even balance equations correctly without understanding the meaning of the formula in terms of particles that the symhols represent. Yarroch (6) found that of the 14 high school students whom he interviewed, only half were able to represent the correct linkages of atoms in molecules. For example, in the equation, Nz + 3 ~ 2 2NH3,students donot differentiate between 3H7 as 00 00 00 and 000000. This lack of understanding of the particulate nature of matter on the part of chemistry students may he related to their lack of formal operational development (7-10) or to their poor visualization ability (11-13). On the other hand it is more likely due to their lack of differentiation of concepts such as solids, liquids, gases, elements, compounds, substances, mixtures,soluti&, etc., and to the lack of instruction in which these terms are related to the particulate nat , w e of matter The ability to represent matter a t the particulate level is imnortant in exolainine ~henomeuaor chemical reactions, changes in state and the gas laws, stoichiometric relationships, and solution chemistry. It is fundamental to the uature of chemistry itself.

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lnstructlon on the Particulate Nature of Matter The age level a t which people should he introduced to the particulate nature of matter is somewhat questionable. If elementary science texts are examined, atoms and molecules are depicted in even the primary grades. The Introductory Physical Science (IPS) text (141, a ninth-grade course devised in the late '60's, introduced the particulate nature of matter at the end of the year from an experimental viewpoint after students undeistood mass, volume, density, and other macroscopic properties of matter. This approach . . would appear to he more appropriate since children in elementary classrooms fail to distinguish between melting and dissolv&, mass and volume, chemical and physical changes, liters and meters, etc. It would seem if children knew more about the "what" of chemical phenomena, they would have the basis to understand the "why" when i t is presented a t t h e secondarv level. However, it is areality thatthe microscopic level is depicted in elementam science texts. This, coupled with the fact that elementariteachers would he familiar with the particulate nature of matter in order to make sense of every day phenomena that they encounter and teach to children, explains the inclusion of the topic as a part of a Basic Science Skills course a t Indiana University. An additional reason for inclusion of the topic is to show students how theories and modelsare an outgrowth of theother science prucrsi skills of h e r v a t i o n , inferring, predicting, hvpofhrsiring, experimenting, etc. ~~~~

Study of Preservlce Teachers Vlews In order to determine prospective elementary teachers views of the oarticulate nature of matter before instruction on the topic, a 14-item Nature of Matter Inventory was devised. The test showed pictures of matter with atoms and molecules depicted as cikles of various sizes and shades. Students were asked to draw a new picture after a chemical c,r p11,siral change occurred. I n ord& to perform well un the test studenti would nred rube ahlt to dLrinyuish elrmenrs, compounds, mixtures, substances, solutions, homogeneous matter, heteroaeneous matter, solids, liquids, gases, and chemicd and physical changes in terms of the particulate view of matter. An example of an item is shown in the figure. No clues were given to students on how the inventories would he scored.

o =Molecule Typical item on the Nature of Matter Inventory.

Volume 64

Number 8

August 1987

695

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and, had this been done, they would have done better. Undouhtedlv this is also true. But the point is this: when students are-not given guidelines they forget about the conservation of particles and they do a poor job in representing matter and physical and chemical changes it undergoes. On the other hand, if chemists completed the inventory, they might make the same mistakes that these students made due to lack of attentiveness to detail or by focusing on a different attribute. Although chemists might not conserve particles or might enlarge the individual atoms unwittingly they would not make e&rs in representing chemical and physical changes! The information obtained from this study has serious implicationsfor the teaching of chemistry. In the past few years there has been an increased interest of science education researchers on problem solving. Instructors of introductory courses know that many students do not understand how to solve problems and frequently resort to algorithmic solutions. In order to he a successful problem solver in chemistry, many factors are involved. Some of these have been summarized hv Reif (17.18).In order to solve a problem correctly, the concepts iovol\.ed in the problems must he understuml and must bt.reculled without prompting. After a preliminnr). description of the problem ismadein terms of what is given and what is sought, the problem needs to be redescribed according to the problem solver's frame of reference. This is frequently done by sketching the physical phenomena invol;ed i n t h e prohlem. For example, in physics acceleration problems it is helpful to sketch first the physical situation and then the forces acting via the vectors. In chemistry i t would appear that depicting the physical phenomena in terms of the articulate nature of matter would also be helpful. The f&lowing examples illustrate just a few of the cases in which the particulate nature of matter sketches might enhance problem solving. Research (19) and experience have shown that many students disregard the fact that 22.4 L is the volume of 1mol of an ideal gas at STP. Students not only disregard ideal gas but also STP. They apply the 22.4 L to solids and liquids as well. If students were reauired to make a sketch of 1 mol of an ideal aas at STP usinz Avogadro's Hypothesis and Dalton's Law of Partial Pressureswould he mare meaningful if sketches were used in solving prohlems. At a recent science fair, a youngster mistakenly reported that

the volume of oxygen produced in the decomposition of water was greater than the volume of hydrogen. The youngster gave a perfectly logical explanation that the oxygen gas would take up mare space because its atoms with eight protons and eight electrons were larger than those of hvdroeen with one nroton and one electron! Disreaard Chemistry students find solution problems involving dilutions and additions of solute very difficult. How can these problems he solved successfullywithout picturing how the addition of the solute to the solvent causes the solute particles to became closer together and the solution more concentrated? The findings from this study and other research about students' views of the particulate nature of matter are cause for concern. Even after the study of chemistry, students cannot distinguish between some of the fundamental concepts on which all of chemistry is based such as solids, liquids, and gases or elements, mixtures, and compounds in terms of the particle model. An increased emphasis on the narticulate nature of matter in introductorv chemistry ) thk courses, such as suggested by James and ~ e l s o d ( 2 0and careful representation of particles by chemists when they are used in instruction might bring about not only an increased ahilitv to solve chemistrv problems hut i t may also help to make" chemistry more Liderstandable by providing-the framework underlying the discipline. Literature Clted (11 osborne,R.J.; Casgrove. M. M. J.Res.Sei.Teach. 1983.22.825. (2) Shepherd,D.L.: Rennor,J.W . Sch.Sci.Malh.1982,82,650. (3) Nnvick.S.:Nusshaum. J.Sci.Educ. 1981.65.187. (4) Eylon.B.;Bon-Zvi. R.: Silberstein. J. NARST. 1982. (51 Ben-Zvi R.; Eylm, B.; Sitherstein, J. NARST, 1982. (61 Yarrock, W. L. J.Rer.Sci. Troin. 1985.22, 449. (71 Herron. J. K. J. ChemEduc. 1978.55.165. (81 Goodstein, M. P.: Howe,A.C. J. Chem. Educ. 1978.171. (9)Milnhohky,L.:Patterson.H. 0.J. Chrm.Educ. 1978,56,87. 110) Good.R.: Kromhout.R. A.:Mellun.E. K . J . Chem. Educ. 1979.56.426. (11) Cosfelio. S. J. NARST, 1982. 1121 Ta1ley.L. H. J. Res.Sri. Teoch. l973,10,263. (131 Small. M Y . ; Mono". M.J. Colie8aSei. Teoch. 1983.41. (141 Hahor-Schaim. U.;Cross, J.R.;Abegg,G.L.;Dodge,J. H.: Walter.J.A.lntroducing Physical Scienec: Prentice: Englewood Cliffs, NJ. 1967. (15) Tobin. K. G.:Capie,E. Edur.Ps~chMms.1981.41.413. (16) G u y , R.; Mc Daniel. E. "Correlate of Performance on Spatial Aptitude Test"; U. S. Army Research Inst., 1978. (171 Reif,F.il C h ~ m E d u c 1983.60.948. . 118) ~ e iF.t Cugnitiv~st~uctureondconceptuai Change; We3t.L.H.;Pines,A. L.,Eds.; Academic: Ollandu. 198b:pp 131-151. (19) Cervellat!. R.:Monturchi. A,: Perugini. D.;Grimellini-Tomasini, N.: Balandi. B. P. J. C h r m Educ. 1982.59.852. (201 James. H. J.; N&on.S. L. J. C h m E d u r . 1981.58.476.

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Number 6 August 1987

697