Elements Old and New - ACS Publications - American Chemical Society

Chapter 10

Downloaded by UNIVERSITE DE SHERBROOKE on March 12, 2018 | https://pubs.acs.org Publication Date (Web): October 30, 2017 | doi: 10.1021/bk-2017-1263.ch010

Element 118: Teaching A New Element to New Students Justin Pothoof,1 Grace Nguyen,1 Dawn Archey,2 E. Prasad Venugopal,1 and Mark A. Benvenuto*,1 1Department

of Chemistry and Biochemistry, University of Detroit Mercy, 4001 W. McNichols Road, Detroit, Michigan 48221-3038, United States 2Department of Mathematics and Software Engineering, University of Detroit Mercy, 4001 W. McNichols Road, Detroit, Michigan 48221-3038, United States *E-mail: [email protected].

The paper discusses how the discovery and naming of the newest elements can be brought into the discussion of the general chemistry class, with an emphasis on Element 118. These two exercises challenge students to use their knowledge of general chemistry as well as mathematics and physics to explain the existence of element 118, and to predict some of its physical properties.

Introduction To the youthful eyes of new students, the periodic table looks like a hydra of numbers and symbols. Unfortunately for those with that point of view, this monster is indispensable to the understanding of science and the reactions that occur on a daily basis in our bodies, on the Earth, and throughout the universe. Therefore, an understanding of the elements, their properties, and their relationship to other elements is stressed in introductory chemistry courses. Perhaps though there are better methods in which to explore, understand, and interpret this monster of science. The current style of teaching the periodic table, elements, and their nuclei gives a skewed vision of their true existence. For instance, Bohr atom images have continuously been used to teach the idea of an atom to students since it was first constructed. The use of this image inaccurately teaches students that electrons © 2017 American Chemical Society

Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


are the same size as protons and neutrons and that they exist in a continuous orbit around the nucleus, which is composed of the neutrons and protons of an atom and account for 99% of the mass in an atom. More accurately, electrons exist within a cloud, but their location cannot be accurately determined. Realistically, what a student is focused on is memorizing elemental symbols and understanding the correlation of atomic number with proton number for their next quiz. It would be fruitful for the method of teaching to evolve with the periodic table. Students are told that the nucleus contains the protons and neutrons, as stated before, and simply accept the fact rather than interpret it. The question that can be asked is: “What does a nucleus look like?” and to have an image of that, the understanding of the forces at the nuclear level should first be known (1–4). Simply stated, the strong force, or nuclear force, serves to hold the nucleus together; it is an attractive force between protons and neutrons, neutrons and neutrons, and, strangely enough, protons and protons. The electrostatic force acts in the opposite direction as the positive charged protons repel one another. Ideally, the nucleus would be shaped in a way that separates protons away from each other enough to minimize electrostatic forces and maximizes nuclear forces. The periodic table is constantly expanding, with four recently-named newly synthesized elements: nihonium (Nh, 113), muscovium (Mc 115), tennessine (Ts, 117) and oganesson (Og, 118) (5–7). The evolution of the table can with relative ease be correlated to the importance of understanding elemental functionality within groups on the table. Seeing where the elements are placed on the table gives indications as to what characteristics and properties they possess, or can at least give a prediction of them. Ideally, the time in which we are living is intriguing enough to make students contemplate the nature of these newly discovered elements in some other-than-class time. This can also be considered wishful thinking on the part of educators, though. Yet teachers can try to challenge young minds by presenting them with this prompt: what does a cup of element 118 look like? This question has of late created a unique opportunity for students to use their knowledge and creativity to produce responses.

The Traditional Presentation of Periodicity The periodic table has certainly been taught to students in one form or another for over a century. For the student seeing this for the first time, it is fair to say there is a lot of memorization involved. The nomenclature of the elements does not follow any system, at least not in any western language, with several names going back to ancient times, a large number of them having been assigned in the eighteenth and nineteenth century, and the transuranic elements and heavier being assigned after the Second World War. Curiously, an examination of the periodic table in Mandarin Chinese does show something of a systematic approach to it, with the wind character being used in the names of all elements that are gases at ambient temperature, and the character for gold in the names of the elements that are metals (this may be because the first transliterations of a growing periodic table into Chinese were undertaken in the nineteenth century as a collaboration between scientists within the Chinese Empire and western missionaries. 196



In whatever way the periodic table is now presented and learned by students and others, memorization has a primary role, and discussions of periodicity often include some explanation of nuclear particles, protons and neutrons, as tiny balls or hard spheres with the protons being positively charged, and the neutrons possessing mass but no charge. Physicists debate the nature and “look” of the nucleus, but most teachers recognize that it is easy to conceptualize a nucleus as some aggregation of small, hard spheres surrounded by shells or clouds of electrons. The continued build-up of nuclear particles, and their orbiting electrons with negative charges to balance the positively charged nucleus, aids in understanding the table in terms of trends in the columns and rows of different elements.

Student Exercise: A Greater Understanding of the Nucleus Nuclear chemistry is not often stressed in the undergraduate chemistry curriculum. Rather, in the general chemistry and inorganic chemistry classes, an understanding of nucleophilicity, electron movement, and loss, gain, and sharing of electrons is heavily emphasized. While some alpha and beta particle interactions may be covered in a general chemistry classroom setting, the understanding of nuclear transmutations tends to be limited to this, an exercise that is really little more than counting nucleons. So the idea of an exercise in which students developed a model of a 118 proton nucleus, using nothing more than geometry and geometric shapes, has an appeal. It can deepen student understanding of how nucleons can come together, and how they can do so with minimal proton – proton interactions. Element 118 was the element of focus in this exercise because it is one of the most recent, least understood, and possibly controversial elements to be synthesized (since less than 10 atoms were detected). Element 118, which has recently been named “oganneson,” was first produced by a team of Russian and American scientists in 2002 at the Joint Institute of Nuclear Research in Dubna, Moscow, Russia; already world renowned for the successful synthesis of nobelium, copernicium, and elements 113, 114, 115, 116, and 117. Element 118 was produced by collisions of californium-249 atoms and calcium-48 ions. It was found to be relatively unstable with a half-life of 0.89 milliseconds. Its rate of decay helps illustrate the idea of an island of stability when compared to a period of time where the half-life of an isotope spikes to 0.16 seconds (flerovium), before dropping back to 1.9 milliseconds (copernicium). Using nothing but a basic geometric model, students were asked to construct a nucleus containing 118 protons, starting with a proton as a central point from which a three-dimensional shape can grow, as well as starting with a neutron as the central point. Using the first starting point, and placing neutrons at the x, y, and z coordinates results in an octahedron with neutrons at the outer six points. This shape has eight faces, which are the next logical positions at which to place nucleons, which would now be protons. Figure 1 shows an example of this. Placing a proton on each of the eight faces of the octahedron results in the outermost points being a cube. The now larger cube has six faces, which can again 197



have neutrons placed on them. This is also shown in Figure 1, and shows the first layer of a repeating pattern, one that can be represented: 1-6-8-6-8… and that can be repeated until 118 protons are in the layers of this growing shape. When students are presented with this exercise, they do eventually come to the realization that just under 15 layers of octahedron – cube repeating layers will eventually occupy all 118 protons, if the starting point is a proton, and the points of each cube are protons. If the starting point is a neutron, the points of each octahedron are occupied by protons, and with only six points at each layer of protons, it will require almost 20 layers to place all 118 protons. Since this is an exercise to aid students in understanding atomic nuclei in some greater depth, it does not matter if the start point for the shape is a proton or a neutron. The idea is that students construct a model of a nucleus that utilizes or occupies the required number of protons. The two different possible outcomes actually encourage class discussion about what a nucleus actually looks like (a concept that is still debatable among physicists). Class discussions about this exercise routinely pull analogies from the macroscopic world. Students can “see” this model better when they think of how fruit is stacked in a grocery store, or how cannon balls are stacked at a war memorial or national park. It is emphasized that these analogies are linked to a belief that protons and neutrons exist as tiny, hard spheres, which is not something upon which all physicists and chemists agree. Yet it provides students with a starting point to a greater understanding of the properties of a heavy atomic nucleus. While students do not tend to turn in a graphic image of a repeating point-octahedron-cube figure that expands to include 15 layers, many of them do produce diagrams that look much like larger versions of Figure 1. In some cases the assignment is hand written, in others some graphics program has been used. Routinely though, an explanation is provided along with the graphic, indicating how many repeat layers of octahedra and cubes are required to reach a total of 118 protons.

Figure 1. Constructing A 118 Proton Nucleus Starting from A Central Proton.

Student Exercise: Predicting Element 118 Properties Another idea presented to students is that the elements exist within groups or families on the periodic table, and within these families are shared properties. Many students are told this and accept it as true, but are never given the opportunity to apply and test this idea. 198 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


The reports and press coverage of the four new elements include Element 118, but because of the small number of atoms made, and the short half-life of them, there has been no chemical or physical behavior to report, as of the present. Thus, a student exercise was developed whereby certain physical properties of the known noble gases could be used to make predictions of the properties of Element 118. These are comparisons of: 1. 2. 3. 4.

Melting points Boiling points Molar volumes Atomic densities

Students were asked to find the known values for each, then construct graphs and extrapolate to estimate the property for Element 118. No restrictions were placed on what type of graph was to be constructed, since line graphs, scatter plots, and bar graphs all provide similar enough representations of the physical property in question that it is easy to see. Figure 2 and 3 show the first two of these four physical properties, with the temperature, in Kelvin, as the y-axis.

Figure 2. Melting Points for Elements in Column 18 of the Periodic Table (y-axis is degree K).

Both of the physical properties graphed in Figures 2 and 3 are well known to students, and they come to a freshmen-level chemistry class with a familiarity of temperatures, knowing for instance the melting and boiling point of water, the temperature of a winter and summer day in their locale, and the ambient temperature of a household. This graphing exercise allows them to predict what the melting and boiling point of Element 118 might be, and even to come to the 199 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


realization that if enough of it were ever made, it could in theory be cooled to the point of being what might be called a noble liquid or a noble solid.

Figure 3. Boiling Points for Elements in Column 18 of the Periodic Table (y-axid is degree K).

Graphing molar volumes and molar densities reinforce an understanding of the physical properties of these elements, including Element 118. Although it is perhaps obvious that students have less basic understanding of molar volume of different materials, or how dense different gases are (a statement that may also be true for the scientists and the general public, as well), the exercise is still a useful one for training students how to make a predictive comparison.

Conclusions These two student exercises were initiated only in 2016, but appear to have proven that even in the freshmen-level general chemistry class, a deeper understanding of the periodic table and the atomic nucleus can be taught than that which comes simply from rote memorization (1, 2). Thus, an understanding of the table becomes more than just how to memorize pieces of the table. Our exercise in using geometric shapes to construct a 118 proton nucleus makes connections between the concepts learned in a chemistry class and those in mathematics classes. As well, the fact that there is more than one “correct” answer to such an exercise opens a larger discussion of what a nucleus actually looks like. Our second exercise uses tools students are already familiar with – graphing – to teach how properties of an element can be predicted. Overall, both exercises bring relevance to the teaching of the periodic table, and can be easily incorporated into chemistry, mathematics, and physics classes. 200


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201 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

Elements Old and New - ACS Publications - American Chemical Society

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