Purpose: Students will work in groups to research, create and present different models of the atom that show the evolution of physicists’ understanding of atomic structure. The class also will learn about the standard model of particle physics and brainstorm how it could be shown in two or three dimensions.
Procedural overview: This activity is designed for three class periods and includes two homework assignments. To prepare for the first class, students will read the online Science News article “How matter’s hidden complexity unleashed the power of nuclear physics,” and answer three questions for homework.
During the first class, students will work in groups to research a classic atomic model and begin preparing a presentation about it. For homework, students can work with their groups or individually to create a 2-D or 3-D physical model of their group’s classic model. During the second class, the groups can finalize their physical models and make their presentations to the rest of the class.
In the final session for this activity, teachers will discuss the standard model of particle physics and have the students brainstorm ways they might create a 2-D or 3-D interpretation of it. To develop their ideas, the class should draw on current scientific knowledge and use resources such as CERN: The Standard Model.
Approximate class time: 3 class periods
Want to make it a virtual lesson? This activity can be delivered remotely using meeting software that allows you to convene the whole class and also to divide students into groups.
Various building materials (examples could include beans, candies. cotton balls, pipe cleaners, packing materials, yarn, tennis balls, baseballs, baggies and other items that can be found at home or in school)
“Dig into atomic models” student worksheet
A projector (optional)
Directions for teachers:
Before the first class for this activity, have students read the online Science News article “How matter’s hidden complexity unleashed the power of nuclear physics” and answer the first set of questions on the student worksheet for homework. A version of the story, “Cracking the atom,” appears in the April 10, 2021 issue of Science News.
1. What is an atom and why do we care about its structure?
Atoms make up matter; they are the building blocks of chemistry. The basic components of atoms are protons, neutrons and electrons. Knowing how many protons, neutrons and electrons a particular atom has will tell you what chemical element it is and how it will behave with atoms of different elements. Atomic structure helps scientists understand and predict the properties of matter.
2. Why has the model of the atom changed over time?
As scientists do experiments and make discoveries, they change their models to reflect new knowledge.
3. What are some practical implications of knowing the structure of the atom?
Answers will vary. Students may note that knowing the structure of atoms can help scientists determine how chemicals will react with each other. For instance, chemists can predict melting and freezing points for chemicals they create when they know the structures of their starting molecules. Knowing the structure of atoms also aids in the design of medicines and materials such as those used in environmental monitoring equipment and solar panels.
After reviewing the homework answers, divide the students into groups. Assign one of the classic models — Dalton, Thomson, Rutherford, Bohr and Schrödinger — to each group.
The groups will work in class and if needed, at home, to research and prepare 5- to 7-minute presentations about their models, to be delivered at the next class. Each presentation should include a description of the model’s appearance, information about the scientists that developed the model and what was known about atoms at the time the model was developed. Groups should build physical representations of their assigned models to incorporate in their presentations. Creativity is encouraged, but students should still aim for accuracy. Alternatively, you could assign model building to students individually. When students bring their models to class, each group can come together to learn from each member’s attempt and put forth the best model or models for their presentation.
As students develop their presentations and build their models, have groups answer the following questions. You can use the questions to evaluate the presentations.
1. What other names have been used to describe the model assigned to you, and why did the model receive the names it did?
Answers will vary depending on the model assigned. The Dalton model is called the billiard ball model or the solid sphere model. Dalton thought of atoms as solid spheres that could not be broken down into smaller parts. The Thomson model is known as the plum pudding model. He thought that electrons were studded over a “sea of positive charge” — something like plums in an English plum pudding. The Rutherford and Bohr models are called planetary models because both have electrons orbiting around an atomic nucleus similar to how planets orbit a star. The Schrödinger model is known as the quantum mechanical model because it incorporates the uncertainty inherent in quantum mechanics. Schrödinger used mathematics to predict the likely location of electrons in atoms.
2. When was your assigned model developed?
Answers will vary depending on the model assigned. The Dalton model was proposed in 1803, the Thomson model was proposed in 1904, the Rutherford model was advanced in 1911, the Bohr model was developed in 1913, and the Schrödinger model was developed in 1926.
3. Although each classic model is named after the scientist who proposed it, these scientists either worked with or were influenced by other scientists. Name some of the influencers.
Answers will vary based on the model assigned. Dalton based his model partly on the work of Antoine Lavoisier and Joseph Proust. The Thomson model is named for Sir J. J. Thomson, who discovered the electron. A physicist named George Johnstone Stoney proposed the existence of electrons in 1874. The Rutherford model was derived from work Ernest Rutherford performed with his colleagues Hans Geiger and Ernest Marsden. Niels Bohr, for whom the Bohr model is named, was influenced by the work of Albert Einstein, Max Planck, Wolfgang Pauli and others. Erwin Schrödinger was influenced by the work Louis de Broglie, Werner Heisenberg and other physicists.
4. What discoveries or new evidence led to the development of this model?
Answers will vary depending on the model assigned. For instance, the Thomson model was developed after the discovery of the electron, while the Rutherford model was created after an experiment yielded results that contradicted the Thomson model. Rutherford and colleagues shot alpha particles at a piece of gold foil and found that some of the particles bounced off the foil instead of passing straight through it as predicted by the Thomson model. The finding led Rutherford to realize that the atom had to have a nucleus of positively charged particles.
5. How is the model that you were assigned different from previous models?
Answers will vary depending on the model assigned. For instance, the Bohr model incorporated the knowledge that electrons tend to occupy specific, discrete energy levels, while the Rutherford model assumed all electrons have the same energy potential. This was conveyed by having the electrons appear to orbit the nucleus in rings akin to planets around the sun instead of equally sized elliptical orbits around the nucleus as it was in the Rutherford model.
6. Are there places your assigned model is still used, and where have you seen it before?
You can still see influences of the Dalton model in depictions of molecules. Atoms that make up the molecule are shown as solid circles or spheres that are bonded together. The Thomson model is not often referenced these days. The Rutherford model is commonly used in popular media. The Bohr model is often used to teach students about electron shells. Students may learn the basics of the Schrödinger model when classes talk about quantum numbers.
At the start of the second class, have the groups finalize their presentations and models. While the students are working, you can walk around to evaluate the models and offer guidance. If there are several good models made by individuals in the group, you can help the students figure out which components to use from the different models to make an improved group model.
The presentations should be given in the order that the models were developed during the 19th and 20th centuries. Doing the presentations chronologically will help the students better understand how the field advanced.
In the third class, introduce students to the standard model of particle physics and the current science that supports it. If you need more information to prepare for this lesson, go to CERN: The Standard Model and DOE Explains…the Standard Model of Particle Physics.
Have the class brainstorm a way to visualize the standard model. Students can use paper, a computer with internet access and a whiteboard for their brainstorming work.
Cover the following questions in the discussion.
1. What is the standard model of particle physics? What are some key things to know about the standard model?
The standard model is a well-established theory in particle physics that describes elementary particles (also called fundamental particles) and explains how these particles behave. The model accounts for three forces in nature: electromagnetism, the strong nuclear force and the weak nuclear force. Elementary particles called quarks make up the protons and neutrons in an atom’s nucleus. Electrons are a kind of lepton, another type of elementary particle. There are force-carrying elementary particles called bosons that allow other particles to interact. For example, a boson called gluon transmits the strong nuclear force, which keeps the quarks in protons and neutrons “glued” together. There are 17 known elementary particles.
2. How is antimatter different from matter? Give an example of each.
Many elementary particles have an antimatter counterpart. Those counterparts have the same mass, but the opposite charge. For example, the antimatter counterpart of the electron is the positron. The electron has a negative charge, and the positron has a positive charge. One of the puzzling things about matter and antimatter is they are not present in equal amounts in the universe. Physicists are trying to understand why there is so much more matter than antimatter.
3. Who developed the standard model of particle physics?
The standard model of particle physics was not the work of one scientist. Many physicists investigating the structure and interactions of subatomic particles did the experimental and theoretical work that made the standard model possible. Notable contributors include James Chadwick, Paul Dirac, Carl Anderson, Enrico Fermi, Peter Higgs and Sheldon Glashow.
4. When was the standard model developed?
From the 1930s onward, physicists began finding more subatomic particles. They wanted to understand what the particles had to do with each other and determine which ones were fundamental (or elementary) particles. Using mathematics and theoretical and experimental work, physicists were able to establish the standard model of particle physics as a theory by the mid-1970s. Since then, more elementary particles predicted by the theory have been discovered. The most recent was in 2012. It is called the Higgs boson.
5. Are there any other common names for the standard model?
6.What discoveries or ideas contributed to the standard model?
Many scientists’ work contributed to the standard model. Here are a few examples. Chadwick discovered the neutron, which helped explain isotopes and broke physics out of the two-particle model of atoms made from only electrons and protons. Fermi advanced the idea that beta decay, the decay of a neutron into a proton within an atom, created an electron and another particle now called an antineutrino. Fermi also discovered many subatomic particles using first natural cosmic rays and then particle accelerators. Higgs and others independently developed a theory for how particles obtain mass in the 1960s; their theory was confirmed in 2012 with the discovery of the Higgs boson, the last of the elementary particles to be discovered.
7. How is the standard model different from the classic models you have studied?
The standard model of particle physics is much more complex than the atomic models that preceded it. Even the most complicated classic models included only three components: electrons, protons and neutrons. There are 17 elementary particles in the standard model — most of them probably unimagined by earlier generations of scientists. The standard model accounts for matter and antimatter, and it contains particles that transmit forces within atoms.
8. What are some weaknesses of the standard model?
The standard model does not take into account gravity, the fourth force of nature, and does not answer why there is more matter than antimatter in the universe. The model also does not explain dark matter, an unidentified, invisible type of matter in the universe. Dark matter appears to interact weakly with all regular matter except through gravity.
9. What visual depictions of the standard model have you seen, and what do you think of them?
Student answers will vary. Visual representations are rare. Most often, the standard model is represented as a “periodic table” of elementary particles with no mention of how they combine to create electrons, neutrons and protons (CERN: The Standard Model). The U.S. Department of Energy website uses a graphic that places the Higgs boson in the center surrounded by a ring of bosons with leptons and quarks in an outer ring (DOE Explains…the Standard Model of Particle Physics).
10. If you were doing a 2-D or 3-D visualization of the standard model, would you include all of the known elementary particles? Why or why not?
Student answers will vary. For instance, a student may say that it would be too complicated to use all of the elementary particles in a 3-D visualization of the standard model. It would be like trying to make a 3-D version of the periodic table. Also, many of these particles disappear quickly, so it would be particularly hard to depict them. Instead, the student may say they would focus on a few elementary particles.
11. Describe how you would depict the standard model.
Student answers will vary. An example answer is provided below:
In my depiction, I want to focus on the basic atom. I think it is important to know that protons are made up of 2 up quarks and one down quark and that neutrons are made up on one up quark and two down quarks. In my 3-D visualization, I would use Starbursts (in their wrappers) to represent the quarks. The up quark would be yellow; the down quark would be red. The proton would have one yellow Starburst (up quark) on each end and the red one (down quark) would be in the middle. The neutrons would be shown with red Starbursts (down quarks) on the ends and a yellow one (up quark). I’d use glitter glue to hold my “protons” and “neutrons” together. The glue represents the gluon, the boson that holds the particles together. I will use tiny zip-lock bags to hold my “atomic nuclei.” The bag can represent the electrons around each “atomic nucleus.”
To convey the idea of antiquarks and positrons, I would again use yellow and red Starbursts and tiny baggies, but everything would be marked with an “A” so the people will know they represent antimatter. To get across the idea that there is a lot less antimatter in the universe than matter, I would put my antiatoms in a quart zip-lock bag and my atoms in a garbage bag. The two bags would be connected with tape or string so people viewing my model would know there is a relationship between the two. The difference in the scale of the two bags is a visual reminder that matter is more common than antimatter.
12. How would you convey the interactions among the various elementary particles?
Student answers will vary. For instance, a student may say that they don’t think the interactions can be shown in a physical model because those interactions happen very fast and some elementary particles don’t last very long. The student may suggest that the concepts covered by the standard model could instead be explained in an animated film.