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I am a 6th Grade Science teacher and I have been teaching Kid Physics to this grade level for at least 5 years now. One of the 6th grade standards is to describe atom using atomic model. I am wondering whether to teach my students the Bohr model or the most current one which is electron cloud model. I feel confident teaching Bohr's model because the electrons are arranged specifically on the shells but I believe that electron cloud model is more current. Thanks for your help. =))

Hi Angelina,
You pose an excellent question. We want the models we use to help inform instruction and not creat new misconceptions. Personally, I teach the history of atomic models and include Dalton, Thomson, Rutherford, Bohr, etc. There is a lesson plan that you may be excited about in this article: Reactions to Atomic Structure
The teacher has her middle school students creating their own models of elements. The article includes the student information/instruction sheet and a grading rubric. How models can add to students' confusion is another interesting tidbit of information that is shared.
Best of luck in planning an engaging unit for your students!
Carolyn

Hi Angelina, While you may not want to go into a great deal of detailed about the electron cloud model, you should at least mention that it is the current accepted model. Your high school chemistry teacher can pick it up from there.

I really agree with the others who commented and say to teach the Bohr model while discussing the electron cloud. The Bohr model sets the stage for understanding of bonding as well as electron excitation (needed to understand light as a particle). If you're able to add some history that shows how technology and science help improve each other more the better! Vanessa

I teach the development of atomic models based on the problems presented and solved. Here is a list of video that consider this perspective Episode 2 of In Search of Giants: Dr Brian Cox takes us on a journey through the history of particle physics. In this episode we learn how J.J. Thomson discovered the fist subatomic particle - the electron https://www.youtube.com/watch?v=IdTxGJjA4Jw&feature=relmfu Episode 3 of In Search of Giants: Dr Brian Cox takes us on a journey through the history of particle physics. In this episode we learn how Ernest Rutherford conducted a historical experiment that revealed that most of the mass of an atom is concentrated in a tiny nucleus made of protons and neutrons. https://www.youtube.com/watch?v=wzALbzTdnc8 Episode 4 of In Search of Giants: Dr Brian Cox takes us on a journey through the history of particle physics. In this episode we learn how Murray Gell-Mann predicted the existence of quarks. https://www.youtube.com/watch?v=3l_h8t_uAnE&feature=channel&list=UL Episode 5 of In Search of Giants: Dr Brian Cox takes us on a journey through the history of particle physics. In this episode we learn how particle physicists have developed a theory that can explain almost everything in the universe in terms of just 12 particles. https://www.youtube.com/watch?v=yPWeJFs5xjc&feature=relmfu Episode 9 of In Search of Giants: Dr Brian Cox takes us on a journey through the history of particle physics. In this episode we learn how the string and weak nuclear forces were discovered. https://www.youtube.com/watch?v=41-LdIFvC9I

You could probably teach both. You can use the Bohr model and say that this is really just an estimation of where the electrons may be found. Then just show the shapes of the electron cloud orbitals and just state the electrons are floating around there. I think the most important thing to say is that there are different energy levels and that electrons repel each other. So if there are 2 electrons they would not be hanging out next to each other.

In the past teaching physical science I have assigned groups a scientist where they had to make a powerpoint regarding that scientists contribution to the atomic theory. I've found this fairly ineffective. I was wondering if anyone has ever tried having the students make an atomic theory brochure, where they have to create a brochure showcasing the contributions of the main scientists to the modern atomic theory from Dalton to the Cloud...or does anyone have any ideas to help formulate this?

Would someone look over this brochure project for me and make suggestions? You can either leave them on here or email me at [email protected]. Thank you!!

Attachments

Atomic_Theory_Brochure_Project.docx (0.02 Mb)

Chris What are your learning objectives for this project? Since completing a class in project based learning , I always like to begin with the end in mind. As I read through this brochure, I feel that students will learn about the scientists more than the science. Could you design a project that focused on the development of atomic theory that considers the theories more than the scientist? So if we start with Dalton What was the theory? What did it explain? What did it NOT explain? How were these weaknesses in explanation addressed and corrected? Dalton's theory was based on the premise that the atoms of different elements could be distinguished by differences in their weights. He stated his theory in a lecture to the Royal Institution in 1803. The theory proposed a number of basic ideas: All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements. Using his theory, Dalton rationalised the various laws of chemical combination which were in existence at that time. However, he made a mistake in assuming that the simplest compound of two elements must be binary, formed from atoms of each element in a 1:1 ratio, and his system of atomic weights was not very accurate - he gave oxygen an atomic weight of seven instead of eight. The next development required a bit of gas law chemistry Gay Lussac formulated his law of combining volumes following experiments exploding together given volumes of Hydrogen and Oxygen and discovering that water comprised two volumes of hydrogen to one volume of oxygen. His law states that when gases react they do so in volumes bearing a simple ratio to one another and to the volumes of their gaseous products provided that temperature and pressure remain constant. Dalton refused to accept the new law as it appeared to contradict his theory of the atom. The difference between the atom and molecule was not clearly understood until the work of Avogadro in 1811. At this point it might be useful to have students explain why Dalton had trouble with this new piece of information. If is also a good time to talk about the difference between atoms and molecules and why a clear understanding of this is important for the development of atomic theory. Diatomic elements were especially problematic. Next Avogadro's Law States that under equal conditions of temperature and pressure, equal volumes of gases contain an equal number of molecules. This hypothesis was not acknowledged in Avogadro's lifetime and it wasn't until Stanislao Cannizzaro, in 1860, demonstrated that it was the solution to the problem of atomic and molecular weights that Avogadro's Law became widely accepted. In 1869 Mendeleev published his periodic table The electron is discovered, J J Thomson publishes his discovery of a sub atomic particle common to all matter. When investigating cathode rays using a highly evacuated discharge tube he was able to use the calculated velocity and deflection of the beam to calculate the ratio of electric charge to mass of the cathode ray. This was found to be constant regardless of the gas used in the tube and the metal of the cathode and was approximately 1000 times less than the value calculated for hydrogen ions in the electrolysis of liquids. Thomson presented three hypotheses about cathode rays based on his 1897 experiments: Cathode rays are charged particles (which he called "corpuscles"). These corpuscles are constituents of the atom. These corpuscles are the only constituents of the atom. http://www.aip.org/history/electron/jjhome.htm http://www.aip.org/history/electron/jjrays.htm http://www.aip.org/history/electron/jj1897.htm http://www.aip.org/history/electron/jjelectr.htm 1911 Ernest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting them using screens coated with zinc sulfide (a scintillator). Rutherford found that although the vast majority of particles passed straight through the foil approximately 1 in 8000 were deflected leading him to his theory that most of the atom was made up of 'empty space'. This model creates lot of problems (1) why don't electrons fall into the nucleus and (2) How does the positively charged nucleus stay together.

OK I got cut off mid sentence without warning and now need to reconstruct a bit :( Booo to this 1913 Niels Bohr applies quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. The energy of the particles in the Bohr atom is restricted to certain discrete values. One says that the energy is quantized. This means that only certain orbits with certain radii are allowed; orbits in between simply don't exist. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit. http://csep10.phys.utk.edu/astr162/lect/light/bohr.html This is a great time for a flame test lab Also on 1913 Frederick Soddy formulates the concept of isotopes, which states that certain elements exist in two or more forms which have different atomic weights but which are indistinguishable chemically. Hmmm so now we have another problem what causes this? If the number of protons in the nucleus defines the element how does this happen? 1925 Austrian physicist Erwin Schrödinger lays the foundations of quantum wave mechanics. In a series papers he describes his partial differential equation that is the basic equation of quantum mechanics and bears the same relation to the mechanics of the atom as Newton's equations of motion bear to planetary astronomy. 1925 Paul Adrien Maurice Dirac, makes a major contribution to physics by devising a form of quantum mechanics, the laws of motion that govern atomic particles. Dirac had the revolutionary idea that the electron could be described by four wave functions, (hence 4 quantum numbers) satisfying four simultaneous differential equations. It followed from these equations that the electron must rotate on its axis, an idea that had been developed by other physicists, and also that there must be states of negative energy. Here is a nice understandable history of quantum mechanics http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/The_Quantum_age_begins.html 1927 Werner Karl Heisenberg (1901-1976) stated in 1927 that certain specific pairs of variables cannot be measured simultaneously with high accuracy. Most importantly, he pointed out that within an atom, it is possible to measure the position, or the momentum, of a subatomic particle such as an electron. However, it is not possible to measure both of them at the same time, because the measuring process interferes to a substantial degree with what is being measured.

OK since I got bit once with a long post cutting off I am now working in bits. 1932 The Neutron James Chadwick used scattering data to calculate the mass of this neutral particle. Since the time of Rutherford it had been known that the atomic mass number A of nuclei is a bit more than twice the atomic number Z for most atoms and that essentially all the mass of the atom is concentrated in the relatively tiny nucleus. As of about 1930 it was presumed that the fundamental particles were protons and electrons, but that required that somehow a number of electrons were bound in the nucleus to partially cancel the charge of A protons. But by this time it was known from the uncertainty principle and from "particle-in-a-box" type confinement calculations that there just wasn't enough energy available to contain electrons in the nucleus. http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrondis.html Various The Strong Force While I do introduce the strong force in my classes, I do not go into the detail 0 albeit provided here (broadly) The existence of the strong force was predicted in 1935 by Yukawa He proposed that the short range strong force came about from the exchange of a massive particle which he called a meson. By observing that the effective range of the nuclear force was on the order of a fermi, a mass for the exchange particle could be predicted using the uncertainty principle. The predicted particle mass was about 100 MeV. It did not receive immediate attention since no one knew of a particle which fit that description. In 1947, Lattes, Muirhead, Occhialini and Powell conducted a high altitude experiment, flying photographic emulsions at 3000 meters. These emulsions revealed the pion, which met all the requirements of the Yukawa particle. We now know that the pion is a meson, a composite particle, and the current view is that the strong interaction is an interaction between quarks. http://aether.lbl.gov/elements/stellar/strong/strong.html Since the protons and neutrons which make up the nucleus are themselves considered to be made up of quarks, and the quarks are considered to be held together by the color force, the strong force between nucleons may be considered to be a residual color force. In the standard model, therefore, the basic exchange particle is the gluon which mediates the forces between quarks. Since the individual gluons and quarks are contained within the proton or neutron, the masses attributed to them cannot be used in the range relationship to predict the range of the force. When something is viewed as emerging from a proton or neutron, then it must be at least a quark-antiquark pair, so it is then plausible that the pion as the lightest meson should serve as a predictor of the maximum range of the strong force between nucleons.

Hi Chris, Tell me some more about your assignment. Is this brochure going to be an introduction to the unit on the development of today's current atomic model or is it going to be an end of the unit assessment? Ruth

It is to be an introduction to the atomic theory and development. Thank you for all the feedback so far Pamela. Like I said, I kinda want this to be an Intro...I need to get the kids doing something else besides listening to me and doing labs. I think with the point system I put into place, that I tried to make sure that they didn't just focus on the scienctists. The scientist information is worth only 2 of the 10 points...so if they just do that, they will not do well on the project.

Hi Chris, I think as an introduction to the unit it is a nice assignment. Just make sure that you focus on method and conclusion of the experiments. So many times, students just learn scientists and dates like they were in a history course. There is nothing wrong about learning science history as long as students are also learning the ways the atomic models changed and why. Write back and share some student samples when you are done with your unit.

Check out this classic BBC documentary http://www.dailymotion.com/video/xq96un_atom-the-clash-of-titans_tech

Does anyone have a good "Cathode Ray Tube" type activity or a "Gold Foil Experiment" activity. I'm also wondering if anyone has a good power point over the Modern Atomic Theory.

Gisella, I would really like to see your powerpoints...can you post them on here...or email them to me. [email protected]

Chris wrote, "[i]Does anyone have a good "Cathode Ray Tube" type activity or a "Gold Foil Experiment" activity?[/i]" Hi Chris, I have an antique cathode ray tube, but I don't have a high voltage power source. When I teach about Thomson's experiment with the cathode ray, I first show my students the cathode ray tube and give a little history. Then I use two video clips. First I use [url=http://www.youtube.com/watch?v=XU8nMKkzbT8]this video.[/url] I let them watch the first 37 seconds of the video. Next, I pause the movie and allow my students to make a sketch of the tube and the cathode ray. Then I play until 55 seconds and have the students sketch the tube, cathode rays, and magnet. I have them predict what they will will happen if the magnet is reversed. I play the rest of the video, pause it again, and allow my students to draw the results of reversing the magnet. Next, I turn on an old CRT computer monitor that is hooked up to my laptop. I let the student distort the CRT screen with a magnet. We talk about similarities and differences to the video they had just viewed. We discuss how Thomson used the results of his experiment to deduce the charge of the electron and the mass to charge ratio. I wrap up the lesson by showing a clip with Dr. Brian Cox about [url=http://www.youtube.com/watch?v=IdTxGJjA4Jw]The Discovery of the Electron[/url]. Before we talk about Rutherford's gold foil experiment, I have my students play battleship on a 10 square X 10 square piece of graph paper. (This activity is from Arthur Eisenkraft's [u]Active Chemistry[/u] text.) Then we discuss how much more difficult it would be to find the object if we decreased the size on the object to one square and increased the size of the board to 1000 squares X 1000 squares. Next I explain the set-up for Rutherford's gold foil experiment. We talk about the results and how Rutherford was puzzled at first with his findings. I show [url=http://www.youtube.com/watch?v=wzALbzTdnc8&feature=relmfu]The Discovery of the Nucleus[/url] and [url=http://www.youtube.com/watch?v=XBqHkraf8iE&feature=related]Backstage Science's Rutherford Goil Foil Experiment[/url]. Then we talk the angle of scattering and what it means. I have the students draw an image of Rutherford's apparatus and label the angles of scattering.

How big of a "ship" do you use for the battleship game?

Chris wrote, 'How big of a 'ship' do you use for the battleship game?'

Hi Chris,
Sorry, I didn't mention the size of ship. For the first part of the activity, the ship is four connecting squares. The ship can be any design as long as the squares are touching.

How did your students like the introduction powerpoint that you were going to use as an unit opener?

The Bohr's model is definitely very interesting topic.The Bohr model gives almost exact results only for a system where two charged points orbit each other at speeds much less than that of light and this is what really fascinates me so much.

Hi, I am just starting a unit on Atoms and Chemistry. My thought is to introduce atoms by using paper clips dividing 8 of them half until we cut a final one in half so it no longer has the properties of a paper clip (like an atom) I was then going to introduce the components of an atom using skittles - red are protons, green neutrons, and yellow are electrons. I photocopied handouts of and atom where the students can place the candy. Also does anyone have a good site where I can get an accurate easy to read copy of a periodic table of the elements? Thanks Kare