# How to Build a Model Atom.

Q:
I need to make a 3 dimensional model of an atom. Can you help with some ideas of constructing this. Thanks
- Troy Reynolds
Jenkins Middle School, Palatka, Florida USA
A:
Troy -

Cool project! The basic structure of an atom is that it has little things called neutrons and protons that are stuck together in a ball (called a nucleus) in the middle, with electrons in a bigger fuzzy ball around that. Neutrons and protons are about the same size, and electrons are much much much smaller. You can use different colors to show which are neutrons, protons, or electrons. Neutral atoms have the same number of protons and electrons. If a neutral atom loses or gains some electrons it is called an ion. Atoms also tend to have similar numbers of neutrons and protons, though the trend is for heavier atoms to have have more neutrons than protons. A normal gold atom, for example, has 79 protons and 118 neutrons.

An interesting fact is that although the "cloud" of electrons that surround the nucleus is much much much bigger than the nucleus itself, most of the mass of the atom (more than 99%) is due to the nucleus.

The number of protons that an atom has is called its atomic number. For example, Hydrogen has one proton so its atomic number is 1. Some other elements are Helium (2), Lithium (3), Beryllium (4), Boron (5), Carbon (6), Nitrogen (7), and Oxygen (8). So far, scientists have discovered elements with atomic numbers of even more than 100! For more information on different elements, check out this . You can click on any element to find information about it, and the atomic numbers are listed on the table itself, so they're easy to find.

As for what to build your atom out of, be creative!

-Tamara /(mods by mbw)

(published on 10/22/2007)

## Follow-Up #1: models of atoms

Q:
i am not sure how to do this project my teacher asked of the class. i am searching on the internet to find a step by step insructional paper on how to make a 3-D model of an atom. Do you have any kinds of resource like what i just explained?
- Becky (age 13)
crosby,tx
A:
We don’t have any special resources for that. More importantly, we have something strange to say about it. To the extent that we understand the small-scale world, including atoms, it has quantum-mechanical properties which are completely unlike any model you can build. For example, the electrons in an atom don’t really  exist at some particular place at any time. Their state is smeared out around the atom’s nucleus. The usual sorts of models people like to display show the electrons as whizzing around like little planets, but that isn’t right.

Mike W.

(published on 10/22/2007)

## Follow-Up #2: What is an atom?

Q:
Hi, I guess the assignment was turned in... I would suggest selecting any kind of object that is roughly sphere shaped from styrofoam balls to jelly beans. Use 3 colors. One color to represent protons, one for neutrons and a third for electrons (preferably much smaller than the p & n particles) Next, use the atomic number for the number of protons and electrons. Subtract the atomic number from the atomic weight to get the number of neutrons. Now glue the protons and neutrons together into a blob. That's the atomic nucleus. Then put the electrons in orbit around the nucleus. You could do this be strining them on a stiff wire wrapped in a circle or maybe draw a circle on a piece of poster board and glue the electrons to the circle, glue the nucleus to the middle of the paper. The atom should roughly resemble planets circling the sun.
- Sue (age >25)
A:
It's true that students could do that, and some of what it would convey about atoms would be true. However, at least as much would be false. For example, a planet circling the Sun is at a particular place and has a particular orbital velocity. The electrons in atoms are not in particular places and do not have particular orbital velocities, except when the orbital velocity is exactly zero. Then there is some indefinite velocity, but it's radial, i.e. toward and away from the nucleus.  That's true of the electrons in hydrogen, helium, and some of the electrons in other elements. That's not a possibility for planetary motion. If the orbital velocity were too small (say zero, for example), the planet would fall into the Sun.

If you were to imagine that the electrons were little classical particles in orbit, they would radiate electromagnetic waves, losing energy,  and the atom would collapse in about a billionth of a second. That was a big puzzle before the discovery of the quantum laws that describe small things.

We love to give simple explanations and pictures when it's possible, but when it's not maybe it's best just to tell students that to understand some mysteries they have to continue their educations.

Mike W.

(published on 11/04/2007)

## Follow-Up #3: cloudy models

Q:
There are two questions from students on how to create a 3-d model of an atom and no real answer for them. How frustrating for us. The second answer is telling us that it isn"t "real" so can"t be done, that is not an answer, the project doesn"t go away for us, we have to do it. Some suggestions like, styrofoam, clay, etc would of been appreciated. Thanks for nothing!
- Ginny
San Diego
A:
We’re trying here to get across both a little of what science has actually discovered and some of the methods used to find things out. Sometimes teachers give assignments that don’t fit well with those goals.

Still, if you have to make models, you have to. Why not use a BB for the dense little nucleus at the center of the atom? Maybe a cotton ball would be usable to convey some of the 'cloudiness' of the electrons, although nothing directly visible really shares the strange behavior of quantum-scale stuff.

Mike W.

(published on 12/10/2007)

## Follow-Up #4: How to make an atom?

Q:
how to make an atom .with the simple things.
- huthashini (age 14)
wgl.Ap.India
A:
Dear Huthashini,
This is a very difficult question to answer.  First of all it is a bit ambiguous.  If you want to manufacture an atom,  you can't go down to the store and buy the necessary materials.  It would be extremely difficult, but in principle possible, to build a complex atom at a high energy accelerator although simple hydrogen-like atoms have been seen at the accelerator at CERN. If you mean by your question how to make a stick-and-ball model of an atom, that is something you can do; although resultant physical model would only vaguely resemble the actual atom.   The reason is that at the atomic scale you have to take into account the quantum mechanical aspects of the individual particles, which behave not as billiard balls but as spread out wave functions.      I hope I haven't confused you too much.  Keep studying physics.

LeeH

(published on 06/26/2008)

## Follow-Up #5: picturing atoms?

Q:
Jeez, These are middle school students asking for help! They don't need to know schrodinger's model yet. Why are you confusing them more than they already are? I understand that they are building a "false" model, but their undertsnading of the atom will require a building and breakdown process. Don't you remember that YOU learned it this way too?
- Jim Lotarski (age 37)
St. Charles, IL USA
A:
Yeah, as you can see we heard similar complaints from some others. It's often a tough call to decide when it's ok to present a falsely simplified answer. We're happy to give Newtonian answers to mechanics questions where relativistic effects can be neglected. We're unwilling to give classical explanations for why some materials are magnetic since one literally cannot even start to say anything meaningful without quantum mechanics. The 'atom picture' questions fall in between.

Here's our rationale for emphasizing the mystery. Almost all the students have seen the toy pictures of atoms with little dots whizzing around. We don't have anything to add to that, and we don't want to use a site which some people treat as a reference source to be saying that's accurate. The only real contribution we can make beyond what the kids are getting in school is to give a hint that there's something weirdly mysterious about the world at that level, and that maybe someday they can understand it.

At any rate a BB and a cotton ball are not such exotic materials.

And no, I didn't learn the Bohr atom, but maybe it is useful for some kids.

Mike W.

(published on 09/08/2008)

## Follow-Up #6: another atom model view

Q:
You guys dont help at all in question 1 through question 5 You are so useless Maybe you should delete this whole web page.....THANKS 4 NOTHING Stupid people I hope You Die!!!!!!! Please help us set up a 3d model of an atom!! R u Mentally Challenged People?????
- Bri (age 13)
A:
Here's another part of the spectrum of responses.

Mike W.

(published on 10/03/2008)

## Follow-Up #7: atom models

Q:
This isn't a question but as you can see I am putting it anyway. Mike W. you seem kind of stuck up. I don't know if its because you are a college proffeseor or if you are just tightly wound. I am in 8th grade and I need help making a "fake" atom model. You were absolutly no help at all. The only help I might have gotten from this site was from other people who have written in this question box. I hope this makes you see how not noce it is to confuse already confused 7th and/or 8th graders. So please next time a middle schooler askes a middle school question please give a middle school answer, or don't reply. Because it is absolutly no help to hear about how confusing an atom really is. Seriously.
- Crystal (age 14)
Norwalk, WI, US
A:
OK, we disagree. I think it's sort of fun that the world is a mixture of parts we understand and parts we don't understand. It gives something to look forward to.

Mike W.

(published on 03/24/2009)

## Follow-Up #8: atoms and MM

Q:
As a teacher, I can say you have not been very helpful to the young people accessing your site for simple help to build a simple atom model!! Kids, three round objects, each a different colour. Two of the round items should be about the same size; the other should be smaller. For example, an apple, an orange and an MM. The larger two objects could be hung or connected together to form the nucleus(proton & neutron), and the small item could be hung, or glued on a dotted line to represent the electron. Hey presto! You've built a simple model of a Hydrogen atom - the smallest of the atoms. Well done!! Now check your Periodic Table to choose a larger atom you'd like to build for more of a challenge, and have fun eating the MM's you don't have to glue onto your model. :)
- Ms. B (age old)
Australia
A:
You're clearly in the majority on this. A few points in our defense:

1. The model you describe is not actually for hydrogen but for deuterium. If you ate the orange, you'd have a hydrogen model left. Since oranges are tasty and good for you,  it would be a win-win move.

2. As we pointed out previously, models of this type are easy to picture but get almost all the basic features of an atom wrong.

3. If students were clamoring to build models of atoms, then teachers would have a good reason to try to supply something, even if it's pretty inaccurate. What we're objecting to is not the students but the teachers, who have decided to make students spend time learning something wrong. The world is full of interesting and challenging things that young students could learn right.

Mike W.

(published on 04/24/2009)

## Follow-Up #9: back to Bohr

Q:
I fully appreciate that the model that is described has inaccuracies. But as far as teaching pupils things that are wrong I disagree. 1) Ideas often have to be simplified for pupils to have a chance at grasping them, jumping in woth oribtal theory just doesn't work. 2) Pupils understand the difference between a model and real life and a valuable skill for them to learn is evaluating. I would encourage any model to have it's strengths and weaknesses identified. 3) I don't know about in the states but in the UK it's the examing boards that dictate what students have to learn not the teachers. 4) This somple model of the atom explains many of the trends and patterns of Group 1,2,7 and 8 of the periodic table at the level they need to understand it. Unfortunately we're not all born with the ability to understand degree level work at birth.
- Mrs B
A:
Thanks for the thoughtful remarks.

Points (1) and (2) are hard to disagree with.

On (3), here in the US, teachers usually have much more autonomy, except for on preparations for the No Child Left Behind tests, unfortunately those don't include science.

On (4), I think the Bohr atom actually leaves the properties of the periodic table extremely mysterious. They don't seem to come in any natural way from the model, so complicated unnatural assumptions about 'shells' etc. are added. That's where it's different from, say, Newtonian physics, which is internally consistent and explanatory over a broad range of phenomena. Bohr leads to trouble right away. It's good at predicting spectral lines of hydrogen, but the students probably weren't worried about those to begin with.

Mike W.

(published on 06/05/2009)

## Follow-Up #10: A comment on atom model building

Q:
As the mother of a middle school student who likes science, I agree with Mike regarding the futility of building models of atoms. Science teachers need to understand that today's middle school students are capable of understanding the general concept of electron clouds, and the impossibility of simultaeously fixing an electron's velocity and position, if it is explained in a straightforward manner as it is in Natalie Angier's popular science book, The Canon. Moreover, it is exactly the kind of bizarre and fascinating fare on which kids this age thrive! Clinging to a mini-solar system model of the atom post-Bohr misses the whole point of the radical changes in physics in the 20th century. It makes as much sense a having students construct geo-centric models of planetary motion post-Galileo. As long as average adult Americans shy away from the sciences, science teachers will not be held to a higher standard. And as long as science teachers are not held to a higher standard, their students will grow up to replenish the ranks of average adult Americans who shy away from the sciences...
- Mary
Connecticut USA
A:
Dear Mary,
Thank you for your comments on this issue.  We have received a variety of others not so favorable to our point of view.    By the way I agree with your praise of Natalie Angier, a science writer for the New York Times.  She tells it like it is, and has won a Pulitzer Prize for her reporting.

LeeH

(published on 06/09/2009)

## Follow-Up #11: atom models redux

Q:
I feel compelled to point out that the individual who indicated that US teachers have far more autonomy than was describe in a prior comment is flatly incorrect. This is particularly true in California where every single lesson must be bound to a Standard in the approved state curriculum. The standardized CAT-9 tests test directly from this standard, and in many school districts, teachers are being instructed to organize their lessons to address the specificity of the exam. In other words, they must teach to the test. This, of course, results in students lacking in critical and creative thinking ability once they leave the K-12 system. I think an assignment such as the one described is actually a terrific opportunity to promote both creativity and critical thinking precisely because it is not possible to construct such a model accurately. My 6th grader asked me to help her find a way to make a model of an atom. After reading about the complexity of such a task on this site, she is more determined than ever to do so. She wasn't happy with the cotton ball idea, because she doesn't think that it does a good enough job of representing the nebulous nature that Mike described. Can anyone think of another way to represent this? Maybe something that catches light randomly?
- Mrs. E (age 45)
A:
Thanks for the thoughtful letter. It's interesting to hear that the traditional autonomy of individual teachers here is gradually being reduced. It's also great that you and your daughter are using the problems with the assignment as a base to do something extra with it.

As for ways of somehow somehow visually representing a bit of the elusive, random nature of atoms, perhaps one could add some little sparkles to a cotton ball. or to some clear gelatinous material. That way light would glint off different parts at different times, sort of randomly. It's not quantum, but fits in with the creative spirit with which your daughter is approaching the job- looking for suggestive visuals, not intended to be a real model.

Mike W.

(published on 08/31/2009)

## Follow-Up #12: atom model

Q:
Hey guys thanks for all the info though there were no direct answers to the "how to make a model" thing but you guys mike mrs b etc. gave me enough reference guides about atomic model like the atomic cloud or bohrs decision i can make my science project and it may end up in our science project exhibit THANKS A LOT =D
- Ferdinand
Laguna Philippines
A:

mike w

(published on 09/04/2009)

## Follow-Up #13: back to models

Q:
My som came home with this exact project (make a 3d model of an atom) today. I am not a scientist or a science teacher but I have an idea about how to make an acceptable model. Elementary school teachers would most likely not be looking for the things mentioned in some of the replies here. Here is what we are doing - I purchased a clear plastic christmas ball that snaps in half. My son then filled this ornament with colored (only 2 colors) gumballs to represent the protons and the neutrons and snapped it back together. On the outside of the ornament is a hole that sticks out - this is where you would usually hang the ball - he made sure that he snapped it back together with half of the hole at opposite ends. He then looped craft wire to form a ring on which he put small beads to represent the electrons. I thnk it looks fine and I am sure his teacher will find it VERY acceptable! I just thought it might help someone else looking for a way to build a model atom for elementary school classes.
- Heidi
United States
A:
This is a very popular topic.

Your model sounds very well designed for pleasing the teacher. It still would be nice to see something more fuzzy and spread-out, like a cotton ball, for the electrons, to start to suggest their actual behavior. On an atomic scale those little bead-like things literally wouldn't last a nanosecond.

Mike W.

(published on 09/22/2009)

## Follow-Up #14: atom models redux

Q:
Mike W you need to get a life or become a professional arguer. The mom with the beads puts out a practical and cheap model and you can't let it go.
- Johnny Ramone (age 53)
NYC USA
A:
Why would someone with 'a life'  be answering questions from strangers?

Mike W.

(published on 09/27/2009)

## Follow-Up #15: electrons, etc.

Q:
I get how to build it but, what is the smallest atom there is? How do I know how much protons, Neutrons and Electrons to have on my model. I know a normal gold atom has 79 protons and 118 nuetron's but, I dont know how many electrons. Even if I did. I dont have enough items to have have hundreds of nuetrons, protons and electrons. Get my delema?
- Chris Kalonji (age 13)
Portland, Oregon
A:
We have one useful point to make. In any atom, the number of electrons exactly matches the number of protons. They have opposite electrical charges, so the total charge is zero. If the atom picks up or loses some electrons, it becomes a charged particle called an ion.

The smallest atom (fewest parts) is a hydrogen atom. It just has one proton and one electron

As a practical matter, it's a nuisance to build even an unrealistic model of an atom which has lots of electrons.

Mike W.

(published on 10/04/2009)

## Follow-Up #16: atom models redux

Q:
Mike W u dnt need to be sooooo technical.... u could dumb it down a little so us not so smart people could make a project to without getting overly confused about atoms when we are barley starting to learn and understand physics! i do apperciate ideas given by other question askers though... thx for that!
- limecoke
US
A:
ok

(published on 10/06/2009)

## Follow-Up #17: atom models redux

Q:
Thank you for giving students something to think about - middle school is not too early to present the "falsity" of physical models. Kids should be aware of this early, and you've presented this clearly and accurately. My daughter has this assignment, and I'll insist she read your explanation and have a thorough understanding of what she is indeed building (and that it doesn't accurately represent an atom). KUDOS.
- Teresa Gresham (age 39)
Mapleton, IL, USA
A:
Teresa- Thanks for this kind note. It's been hard to convey to people that this site is about helping people think scientifically about the world, not about helping do school assignments.  Just for entertainment purposes, I'll post some less favorable responses.

Mike W.

(published on 10/12/2009)

## Follow-Up #18: atomic teaching

Q:
What an interesting discussion! I'm amazed at how emphatic some people about their points of view. As a middle school science teacher, I love this project for the purpose of presenting inaccurate models. As a few people have mentioned already, middle school is a GREAT time to get students thinking critically about scientific concepts. Just as the Bohr model was historically used as a stepping stone to our better understanding of atomic structure, I think it's an essential part of a student's understanding of this structure. Yet despite how much we might like the simplicity of this model, it's important for students to take that next step. Even after completing an assignment of constructing a 3-D Bohr model, middle school students are usually curious enough about the world around them to be fascinated by the more current understanding we have. A discussion about how this could be modeled in 3-D would be very interesting. This is where I like to share computer-generated models with my students. Not only will students be able to better grasp the idea of the electron cloud but these models generally also include motion which can help students to see the more erratic movement of electrons within this cloud. Thanks to everyone who has contributed to this conversation! It has certainly informed me as a teacher about the sometimes unspoken repercussions of assignments I give. Mike--you'd be amazed at how little academic freedom is given to public school teachers these days. We do our best to keep things interesting and meaningful for students but in many cases the concept of educational "standards" has taken on a new meaning of what/how/why things are taught in today's classrooms.
- Mr. P (age 23)
Miami, FL
A:
Mr. P. -

Thanks for keeping up the good work in a tough situation. Have you seen this set of computer simulations?

It is amazing to somebody who went through the public school system many decades ago that the structure has changed so much. It's even a big change since my kids went through.

Mike W.

(published on 10/20/2009)

## Follow-Up #19: philosophy of teaching

Q:
I am a chemistry teacher. I hold a B.S. in biochemistry, an M.S. in nutritional sciences, and an M.A.T. in science education. I am mortified and livid every day at the substandard product my middle and elementary school teachers send me. I want kids to know HOW to think, not WHAT to think. I am sick to death of trying to reteach students good ideas and thoughts based on the lies about atoms they learn in middle school. This is akin to being a biology teacher. Why don't we teach kids how good it is to put leeches on their bodies, or about black bile, phlegm, blood, and green bile, and then send them to high school to learn how things really work? It's easy to be lazy and teach kids lies. I am glad they don't do that in my district. Oh, and by the way, I taught college at an R1 university too (actually two of them, both land grant schools.) I am mortified at the misconceptions our science students have there as well. Don't do our kids a disservice and lie to them. Scaffold them properly. Examine evidence. Do some experiments. Show them Rutherford. Do math (kids can do ratios). But don't lie to them. They are the ones going to Mars.....don't they deserve better?
- Scott (age 41)
Chemistry Teacher, USA
A:
Thanks for joining the discussion.

Mike W.

(published on 10/22/2009)

## Follow-Up #20: atom models again

Q:
Not so much a question, but I think the reason a lot of people have problems with your answer is that they think the Bohr model is basically right, and there are just some esoteric tweaks necessary to make it compatible with quantum mechanics. To them, it seems like you're criticizing a child's model of the solar system because he's drawn the planets' orbits as circles, rather than ellipses. They don't get that the Bohr model is in fact almost totally wrong, and in fact badly misleading, since it implies that subatomic particles behave just like macroscopic objects, only on a very small scale. Of course, it could be just the usual case of people getting upset when scientists tell them things that are hard to understand. I would have assumed that someone asking this website this question would want a more knowledgeable answer than "glue little colored balls and sticks together" - it doesn't take a PhD physicist to tell kids to do that.
- Eric (age 37)
Los Angeles, CA, USA
A:
Thanks,

Mike W.

(published on 11/01/2009)

## Follow-Up #21: thoughts on education

Q:
My 6th grade son came home with this assignment. Some here have said this is a lame assignment. However, you have to begin somewhere. There is only so much you can do at this level. At least it gets them thinking and using their imaginations a bit. I think most of us forget what it is like to be that age. We were no Einsteins then. There is almost no experimentation or hands on stuff in school right now. Every moment is scripted. I used to volunteer to do math games every other week with my kids classes, now they don't have time to spend an hour every two weeks. State requirements dictate every minute. I went to high school in the 70s and learned about the atom the "old" way, but have become educated in the real world way from my own curiosity. I don't leave my kids' educations up to the schools. Be active in their and supplement what they learn at school.
- John
A:
One thing I've definitely learned from this whole question is that there's a major unmet need for some sort of forum in which teachers, students, and parents can thrash out issues in education. We're happy to accidentally supply that for this particular issue. Maybe we can encourage our friends in the Ed School to do something more systematic.

Mike W.

(published on 11/05/2009)

## Follow-Up #22: Bohr model

Q:
I would also like to add a comment. I have heard a lot about how wrong this model is. However, this was a step in discovering how the atom looked. I show my students what Democritus and Dalton thought the model looked like. We discuss Thompson's Plum Pudding model and Rutherford's gold foil experiment. We talk about Bohr's model, then get into the current quantum physics model. This is all with 14 and 15 year old kids! I let them make a Bohr model of an atom for extra credit, but I do feel that this is a useful project. It illustrates the nature of the nucleus and at least gives the kids the ideal of what the energy levels mean and where the valence electrons are, etc. No, it does not accurately depict the current model as far as the electron cloud. But I would not attempt to teach my students general relativity without a background in Newtonian mechanics and I would not want to teach atomic structure without some discussion of the Bohr model. What people need to remember is that most of our high school students struggle with the concept of the electron cloud. Our text doesn't even discuss the Schrodinger model or the Heisenberg Uncertainty principle, it is considered too deep by the experts that write the books. I introduce it, but all too often all I get are blank stares from my students. If someone can come up with a better way of teaching this to 9th graders, I would welcome the advice.
- Kevin (age 43)
Duluth, MN USA
A:
Agreed, it's tough to make this leap. Historically, it was heroic of Bohr to propose his incoherent half-way model, probably a necessary step toward quantum theory. It's tough to know whether it serves more as a bridge or a dead end in modern teaching.

We share your wish for better ways of teaching this material.

Mike W.

(published on 12/08/2009)

## Follow-Up #23: atoms and art

Q:
What a great discussion. My 8th grade daughter and I are here because she too was given the assignment to create an atomic model for gold. I myself was frustrated. This assignment is as old as dirt (I did the same thing in 8th grade) and I view this assignment as narrow minded busy work, with a grading rubric(200 pts!)that resembles more an art project than a scientific project. The students are not encouraged to explore and gain an understanding (however rudimentary) of quantum physics, which I wish I would have had a better understanding of in school. For extra credit, she was told to show the atom in a molecule....what?!?!I am still frustrated with the assignment, but at least it brought us to this site and very informative discussion. This will all be a great help in completing a successful art, er science project, and we both learned something new here. Thank you.
- Mary, mom & former bio teacher (age 45)
chgo, IL
A:
Thanks!

Mike W.

(published on 12/10/2009)

## Follow-Up #24: atom models with balloons

Q:
Given the same challenge for my middle school child and their atom model extra credit project, I knew immediately that I did not want her to just make another planetary model atom. So this website was the first I came and I certainly got some ideas about what _not to do that amplified my desire to try and teach her something more in line with current thinking on this topic. What we ended up modeling was the carbon atom using the sp^3 hybrid orbitals depicted with four balloons as lobes in a tetrahedral configuration. The inner 1s shell was depicted with another sphere, in the middle, with an over-sized nucleus; for illustration (I felt a little uneasy about that part); in the center, with six neutrons and six protons. Although I understand that the orbital hybridization theory fails to predict experimental outcomes in all cases. This quantum model of carbon at least depicts the electron clouds in a snapshot of one state and it has a geometry that can be appreciated at a macroscopic level; the tetrahedral bonds in methane or diamond. What do you think? David
- David Galloway (age 44)
Seattle, WA, USA
A:
I think you did a great job. There are of course further layers of quantum mystery which cannot be captured in a classical model, but you've done a wonderful job of capturing that the electrons exist as clouds in interesting wave-like patterns which then show up in chemical properties.

Mike W.

(published on 01/12/2010)

## Follow-Up #25: atoms

Q:
Wow. I came in search of an idea for having my kids make a model of an atom and came away with a HUGE education. Isn't the internet an amazing place? This homeschooling family is scrapping its plans for today and doing some serious and real research about atoms. The things we take for granted... You linked one site on a previous response. Any others you'd recommend for us? Thank you so much.
- Sue S. (age 45)
Illinois
A:
I can't think of any other sites as good as that one (). It has a lot of different programs you can run, looking at the behavior of a variety of different wave functions.

Mike W,

(published on 01/27/2010)

## Follow-Up #26: freezing atom in time?

Q:
Your website was a huge help with simple easy to follow instructions. Not really! Not even close! The audience you are attempting to communicate with are only in 7th or 8th grade. Thank you to the teacher who did explain it in easy enough terms, and the M&M's were a nice touch. Granted, these kids are not truly building an "atom". They are building a free-form model of an atom; frozen at one point in time. So in theory, no cotton ball - it truly is just hanging there in planetary mode. Good luck to others who are struggling with how to teach CHILDREN (not college kids) the basics.
- Ash's Mom (age 42)
Utah
A:
One of the reasons that we didn't want to endorse the various atom model ideas is that they really convey wrong answers. The idea that at some particular point in time the electrons are actually at particular places is the most importantly wrong of those ideas. Their spread is not just an average property of little things running around over time. The electron state really is spread out.

So, whether it is good or bad for students to make these models as a first step in understanding, this site, which is used by various people as an information source, shouldn't be the place to give those incorrect pictures.

Mike W.

(published on 01/30/2010)

## Follow-Up #27: Bohr and quantum chemistry

Q:
I'm a teacher who has asked her students in Grade 8 to do the following project. Like a previous teacher, we have done an atomic theory timeline showing how different scientists ideas have contributed to our ideas of what an atom 'looks' like from Democritus to Schroedingers. And they are all contributions after all. Being a physical (quantm) chemist, I have emphasized the 'mystery' in the electron cloud and the complicated mahts that goes into it. But beyond that it would be difficut for a student to understand at that stage. However, Bohr's model is still useful to chemists when it comes to explaining bonding behaviour. It also lets them think about the currency of atoms in terms of protons, neturons and electrons. An interesting idea would be to have the students critique their own models afterwards for inaccuracies, or proportions they were unable to represent. Or try to recreate the timeline by having students work on the different models, Rutherford, Bohr, modern-day etc. Thanks for the thoughts, just thought that shooting down Bohr's model completely is not fully fair?
- Anonymous
A:
Another thoughtful contribution.

Thanks, Mike W.

(published on 02/24/2010)

## Follow-Up #28: atom models

Q:
Bravo! I was searching for ideas to teach my gifted third graders the concept of atoms. Yes, I was only looking for the standard "how to build a model atom". Not anymore! I am off to do some more research. Thanks for the information.
- Ms. A (age 40 ish)
VA
A:
welcome!
Mike W

(published on 02/25/2010)

## Follow-Up #29: atom models

Q:
We're another homeschooling family now rethinking our science lesson for the day! I am teaching my two second-graders about atoms, but I think we'll dispense with the model for now! Thank you for the education.
- C. Peterson (age 37)
WA, USA
A:

Mike W.

(published on 02/25/2010)

## Follow-Up #30: model details

Q:
I'm another 8th grader stuck on an atom model. I've read all the follow ups on the previous questions and i am doing muy project. But the thing is, i'm stuck on whether to put the nucleus in a semi ball (one side open to see the inside) and place the protons and neutrons inside, or whether to just put the protons and neutrons together without placeing them inside an semi-ball. Today is saturday, prject due monday. Can you reply by then? Thank You!
- Tracey (age 13)
U.S
A:
There's no particular reason to use a semi-ball. The plain cluster of nucleons isn't very accurate, but if the 'ball' conveys anything, it probably makes the result less accurate. I'd keep it simple.

Mike W.

(published on 02/27/2010)

## Follow-Up #31: going atomic

Q:
I received this project for school and decided to do some research. I came across this website and I only benefitted from the questions. Mike W, you suck.
- Anonymous
A:
There's been a range of views on that issue.

Mike W.

(published on 03/06/2010)

## Follow-Up #32: emotional support

Q:
Wow! I can't believe all the flak the Physics Van is taking for generously offering the time and energy to answer this question. (Although I admit I didn't read all of the follow-ups - there are just too many.) My question. How do you feel when you've thrown time, energy and passion (and proabaly a career) into something like physics, when in your passion for learning you try to help strangers, but fellow humans, by trying to answer questions and sharing what you know, and yet a few people respond to your altruistic efforts with little more than an indignant sense of entitlement that you didn't do their homework assignment for them the way they wanted? [Just wondering. Perhaps the question is rhetorical - I think it would make me wish I had gone into APPLIED physics ... maybe weapons systems ...] Anyway, thanks for sharing your interest and knowledge. I've appreciated your contributions in the past.
- Scott (age 41)
CO
A:
Yeah, it can be a bummer. The thing that really sticks in my mind though is that the very idea of trying to learn about things, as opposed to trying to just do what you're told, is unfamiliar to a lot of the students. You can see where, if they have been taught for years that their job is to follow orders, they would be confused and angered if some authority figure didn't help clarify the orders but instead started going on about how there was a flaw in the orders. It would really be interesting to know how the reactions correlate with other measures of personality traits.

Mike W.

It's no big deal. The polemics really don't bother me.  It's water off a duck's back.  There is a fundamental pedagogical question here though:  do you increase or decrease overall understanding by first introducing a model (Bohr atom, for example) that is not the complete answer but a step in the right direction. Even the physics community embraced it in the 1910's and 20's.

LeeH

Lee- True, good point. But  there's also the question  of what is the particular role of this sort of site, providing information which seems to be taken as reliable. Mike.

(published on 03/09/2010)

## Follow-Up #33: teaching about the atom

Q:
Wow! I remember feeling betrayed when I found out Columbus did not discover America and it just keeps on going! The comments I have read lead me to believe people underestimate what children are capable of understanding. This will be my first year teaching my boys (homeschooled) formal science. Until now we have just focused on observing nature and talking about whatever comes up. They have done some experiments, but self-directed and designed to answer some question they have. I decided to start with the atom (backwards according to public school "standards"). I may attempt to make some kind of model (maybe use some kind of spray for the electron cloud?) but I intend to do some more research and explain how can never be a real representation of an atom and why it is such a mystery. I know my kids can understand this and they are not unusual except that creativity and freedom of thought are encouraged. I love your honesty. When I do research so that I may teach, I am not looking for lies or information "watered down" to a "kid level."
- Christina
Indiana
A:
Christina-

Thanks,

Mike W.

(published on 08/12/2010)

## Follow-Up #34: my defense

Q:
Honestly some of yall need to leave Mike alone because with all of you coming an asking him questions like how to make a 3d model its kinda like wow like he's only one person and if ur not gonna accept his idea then leave, dont complain about it. I think he has helped me out, see me i just used clay,toothpicks,strings,straws,or anything that i could find around the house that was similar to the picture of the atom my highschool teacher gave me. But I do think the project of making a 3d atom is kind of weird but oh well
- Aliyah (age 15)
Louisana
A:
Yeah, like Aliyah said.

Mike W.

(published on 09/22/2010)

## Follow-Up #35: ancient china etc.

Q:
I read this discussion with a great deal of amusement. I teach 6th grade science, and although we discussed the atomic model, I am never in my life going to ask them to build a 3D version...thanks to these postings! I actually came to this site to look for information on understanding the atomic model in order to write a udl book for an assistive technology class...after hearing all of the controversy, I think I'll write my book on the contrasting roles of men and women in ancient China instead! Keep your head up, Mike...you're doing fine! I can assure you, public school teachers in America are doing their best to keep rigor in the classroom!
- andie
keaau, HI
A:
Thanks, Andie.

I didn't mean to drive people away from science questions, just toward focus on ones where we can give decent answers.

Here's a for-instance of a visual sort of thing. Take a somewhat filled balloon. You can dip it in warm water and see it expand. Or cold water and see it contract. You can discuss with the kids a model of little particles inside slamming against the rubber, more when they're hot and less when they're cold.

If you have some dry ice you can put a little inside a balloon and let it evaporate, filling the balloon. Then you can discuss how molecules can pack together in a crystal or run free as a gas. Little 3-D models of that don't distort the important parts of the picture too much.

These are problems for which kids can play with and make decent models which convey something important about how the world works.

Mike W.

(published on 10/06/2010)

## Follow-Up #36: Where is the electron, really?

Q:
Hi Mike, In FollowUp#33, you said that the electron state really is spread out. What did you mean by that? Someone else earlier described it as a smear. The electron is a particle isn't it? So it must exist in a specific location within the cloud at any specific point in time even if we cant predict exactly where that will be? Or have I missed something fundamental? Looking forward to your reply. This has got me thinking.
- Tsp (age 40)
A:
You've put your finger on the central question and most common misconception. As for whether "the electron is a particle", I'm not sure what that abstract phrase means. However, your next description has the meat of the question: whether or not an electron "must exist in a specific location". The answer is no, as we explain below.

The question applies generally to all sorts of quantum variables which can give a range of possible outcomes when measured, not just the positions of one particular type of "particle". For many years it was widely assumed that even when quantum mechanics couldn't tell us what results we'd get in such a measurement, an actual value did exist. Then, in the mid 1960's, John Bell made some simple, beautiful arguments that showed that any description based on that common-sense assumption would give different results than quantum mechanics for certain categories of experiments. Quantum mechanics violates what are now known as the Bell Inequalities, relations obeyed by any local realist theory, including but not limited to ones which assume electrons have actual positions. (Local realist theories are ones in which outcomes have local causes, i.e. actual values of the variables which are measured.)

So what about actual nature? It took some years for the experimental tests to be done, but by now they have become undergraduate laboratory exercises. Nature violates the Bell Inequalities, just the way quantum mechanics predicts. Local realism is false. An electron has no specific position.

Thanks for giving me an opportunity to clarify this central point of modern physics.

Mike W.

(published on 11/22/2010)

## Follow-Up #37: confusing?

Q:
I'm sorry to say this, but it's not a totally 'incorrect' method of bouilding an atom. Maybe teachers want students to understand the principle of the Bohr Modle to let students grasp the idea of atoms. I mean we even studied the plum pudding model(also called chocolate chip cookie model), and it's definatly wrong! Please stop confusing middle schoolers like me. We don't need to know quantum macanics yet! (please excuse my spelling)
- Rebecca (age 13)
A:
Hi Rebecca- We don't want to confuse anybody. It's hard for us to know what the best steps are in teaching this material. You make a nice case that it's good to go through a variety of models. However, we don't want this particular site, which sometimes is taken to be an accurate source for information, to be the source for scrambled ideas, even if it turns out they're a useful learning step.

Mike W.

(published on 12/02/2010)

## Follow-Up #38: specific model-building ideas

Q:
Well, All I've got to say is, that Mike W, your ideas and theories are great and useful, but for the kids, I'd say that they should follow the teacher's directions, but if you like Mike W's ideas, you can add soe spark to your project. Im into science myself, and for my project, I did this for the element Neon: I used a styrophome ball, and stuck 10 red coloured balls and 10 blue coloured balls all around it. and then using thick wire, I stuck two out going random directions with a short wire, and eight others with a tall wire. Just an idea ro help your developing brain. Do you approve of my idea, Mike? Cheryl Hi folks, Oh, Mike I'm sorry, I fogot to say that I used cotton balls for the electrons by fluffing them out so that they loook more like tufts of wind. And also, Children, Mike is only trying to help you. Give him a chance, will you? you all seem very bright, knowing to come to a site for help. oh dear, the cat is calling for her milk. I must go to Kentucky. They do have the best gourmet milk, you know. farewell! feel free to call me Cheerful Cherry! ~Cheryl
- Cheryl T. (age (Elderly))
Atlanta, Georgia
A:
Cheryl- I've combined your two notes into one for ease of reading.

I think I can picture your idea, and of course find the cotton-ball part appealing as a way to suggest the fuzziness of where the electrons are located.. Plus you've put in some suggestion of randomness. So this seems to be getting at the idea of suggesting something unusual at the atomic scale.

Mike W.

(published on 01/03/2011)

## Follow-Up #39: atom frustration

Q:
Dear Mr. Mike W, I looked at your site in an effort to find ideas/instructions on how to build an atom model. I am very disappointed by your level of "unhelpfulness." Your responses are a joke and a waste of time. Frustrated Parent
- Frustrated Parent (age 21+)
A:
Dear FP: What I'm wondering about is how this note and the next one to come in (which ended up posted just above), submitted very shortly afterward,  managed to coordinate on the word "joke". Is this a coincidence or is one of our friends pulling somebody's leg?

Mike W.

(published on 01/09/2011)

## Follow-Up #40: joke?

Q:
This isn't a question.(sorry for still checking the box ..lol) But I would like to applaud your answers to all of the kids who asked about building models. Sometimes simply knowing the answer, or how to "do" something isn't as useful as sitting back and pondering the intricacies of a question, or at least being aware of the intricacies that exist. If just answering a question or doing a project eliminates the possibility to be intrigued and interested in scientific concepts. And consequently when you get to higher education you get overwhelmed by detail and complexity because as a kid you never where exposed to the "truth" about science. Anywho keep up the good work. And thanks for the site.
- joke (age 20)
cambridge,massachusetts
A:
OK, I have a lot of friends in Cambridge, so maybe this is from one of you? Was the almost-simultaneous note on the other side of the issue, also referring to "joke",  maybe a set up for this one?

I suppose we should track IP addresses, but that's too much hassle.

Anyway, thanks for the very thoughtful support.

Mike W.

(published on 01/09/2011)

## Follow-Up #41: further atom thoughts

Q:
Mike~ Thankyou. Yes, I think that by randomizing the position of the electrons, protons, and neutorns, it helps the better understanding that there isnt just a straight line of electrons, and the neutrons and protons should be clustered. Those are just some ideas to help the children. ~Cheryl
- Cheryl (age (Elderly))
Atlanta, Georgia
A:

Mike W.

(published on 01/10/2011)

## Follow-Up #42: old questions

Q:
- Mehran (age 60)
Miami
A:
Thanks for pointing out those old items, Mehran. Your questions hit right at the heart of these issues.

It was alarming, however, to notice your age on the form, and realize how long we've both been at this.

Mike W.

(published on 01/17/2011)

## Follow-Up #43: home-schooling quantum physics

Q:
- Monica (age 46)
central New York
A:
Monica- That site didn't open properly yet on either a Mac or Wintel.   Meanwhile, it's hard to resist posting your very encouraging words.

Aha- That site seemed to open fairly well in another browser. My impression is that it has a lot of useful vocabulary but not much science. If students remember the vocabulary, it will help them to know what people are talking about sometimes.  At some point, if they want to learn some science, they'll need to pick some smaller set of topics and think about them enough to get a feel for how the models connect to things people observe.

The actual pictures on the site show the electrons as dots moving around. They aren't like that in several regards:
1. They aren't at particular places, even temporarily.
2. They do not have particular velocities even temporarily.
3. The positions of their fuzzy clouds typically are not changing in time.
4. Their fuzzy distributions of velocities typically are not changing in time.

Mike W.

(published on 02/08/2011)

## Follow-Up #44: How to teach about atoms?

Q:
While I agree that learning a particular method or idea only to have to un-learn portions of that method or idea later is a travesty, I think the problem with attempting to describe the quantum nature of atoms is, at its heart, the inability for younger children to grasp more abstract concepts. Middle schoolers need more concrete examples, diagrams, and models to help them understand the world, whereas high schoolers and college students are much more capable of sitting back and imagining what something might look like based on a vague description. So I suppose my question is this: how do you propose to teach a middle-school student (in the most accurate way possible) about the nature of an atom's structure in a way that they can grasp? We simply can't ask them to sit just sit around and ponder such an abstract concept, can we? Models are not (quite obviously!) the way to go, so how can we best pass on what we understand?
- The Woodsman (age 26)
Normal, IL, USA
A:
Good question. I don't know of much research on what works best for this. It may well be that heading down the planetary model path and then unlearning it is as good as anything. (It still wouldn't make sense for us to be trying to push a planetary model here.)

For middle-school kids perhaps it's possible to just say that particles are fuzzed out. The electron fuzz is pulled in toward the nucleus, sort of like how the earth is pulled in toward the sun. It just gets too hard to squash it in, so that's why it stays fuzzed out.

Mike W.

(published on 02/23/2011)

## Follow-Up #45: Kerri from Knoxville

Q:
Sorry, yet another person without a question (because you answered it so wonderfully already). What at treat to go looking for real information and find it. Mike W. you are my hero: I wish I could be as even-keeled when people throw tomatoes at me. If those students who came here looking for answers would actually read the posts and your incredibly thought-provoking responses, they really would learn something. First, they would discover that there are plenty of simple ideas for how they can just do the project they have been told to do. Second, they might just get their minds blown, like I did! My daughter will be reading this thread when she comes home, before making her model with a BB and cotton balls (because the bottom line is she has to make the darn thing), and she will be able to explain to her teacher why she choose to represent an atom of Argon in that manner. Awesome!
- Kerri (age 46)
Knoxville, TN
A:
Kerri- Seriously, notes like yours make life seem worthwhile.

many thanks,

Mike W.

p.s. Don't forget, a few sequins embedded in the cotton ball will help hint at the strange quantum behavior, where the fuzzed-out electron can briefly get much less fuzzy, if probed the right way.

(published on 03/10/2011)

## Follow-Up #46: slave labor

Q:
Funny stuff. I laughed until I cried. My wife (see above) sent me the link. My favorites are #7 and #13. You are clearly a graduate student or other form of legal slave labor.
- Paul (age 47)
Knoxville, TN
A:
My favorite is #37, because it finally focuses in on the core weirdness.

Actually, the state retirement system pays Lee and me to do nothing, at least until the state goes more broke. We do this for fun.

Mike W.

(published on 03/10/2011)

## Follow-Up #47: bigger atom models

Q:
I agree that it's great to think of electron clouds, and the cotton ball is a good idea. But with a cotton ball how do you get across the idea that H has 1 electron, Na has 11, and I has 53? Maybe larger cotton balls for bigger atoms, but what if I'm in charge of Na only and all my classmates are a "Bohr?" 11 sequins? That doesn't seem very satisfying.
- matt (age 56)
Boston, MA
A:
Tough question. As we mentioned in the previous discussions, it's impossible in principle to make a classical model of even a simple quantum system such as a hydrogen atom. Thanks to some creative readers, we came up with some sorts of kluges which suggest some quantum behavior.

Now you raise a different question- the kluges are just plain difficult to construct for atoms with many electrons. I guess you could imagine taking bunches of cotton thread and dying it different colors to stand for different electrons. Then you could sort of weave it together so that the different colors had the shape and scaled size of different orbitals. Ok, this is way too hard, even for a fairly small number of electrons, and you mentioned 53.

We're stumped.  Maybe a sort of jello (clear silicone, so that it doesn't just fall apart or get eaten by the Bohring classmates) with a number of sequins equal to the number of electrons? A terrible model, but we live in an imperfect world.

Mike W.

(published on 04/09/2011)

## Follow-Up #48: arsenic models

Q:
ok so i am in high school nd i am making a 3-d model of an atom nd i was wondering how many protons nd neutrons would go on an atom for the element arsenic.? or i was taking to my uncle bcuz we were both sitting here reading some of the answers to the questions nd we were wondering if u can send us insturtions or a picture of an model so we can get an idea of how to make one.? sence u guys seem to know how they are made. why cant you guys just help out instead of telling us tht the way tht were making them is wrong bcuz even tho it is wrong it is still teaching us abt an atom model. were only in middle nd high school we are not expected to make an real model. the whole point of us to make these models is to learn nd understand the atom model, not how its made.
- kayla (age 15)
mi
A:
We can help with one thing: the stable version of the arsenic nucleus has 33 protons and 42 neutrons.

Beyond that, we don't have much to add to the long discussion above. Just to repeat the main point, what this site is about is just to help people learn a little of what we know about the world and a little about how we know it. Sometimes that goes along nicely with school assignments but sometimes it doesn't.

Mike W.

(published on 04/10/2011)

## Follow-Up #49: Bromine model

Q:
- Rebecca (age 14)
Seattle, WA, US
A:
Rebecca- The problem here is that, even if I drop any attempt to act like a responsible physics instructor, I can't think of how to do that assignment. Bromine has 35 electrons. You can count up the numbers of 1s (2), 2s (2), 2p (6).... You can then decide how to model them. S's should be represented by some sort of spherical ball. The p's get a two-lobed loop. Some of the d's can get a sort of cloverleaf pattern. The ones with low numbers (say 1s) should be small, bigger numbers (say 2s) bigger. You can get a nice picture from this site:

How to actually get this all put together is way beyond me. I was no good at that sort of stuff in school.  If you figure out how to do this, it seems that lots of others would like to hear about it. Sorry to be of so little help, but we wish you good luck.

Mike W.

(published on 06/10/2011)

## Follow-Up #50: On teaching science

Q:
This is not a question, but I am an English teacher. I have noticed that your responses seem quite controversial, but I have just been given a science class to teach and have no idea how to do so. I was trying to figure out a way to assign students the same assignment I saw other science classes giving with building a model for an atom. I realize your answers do seem confusing for an 8th grader, but as a teacher, I really appreciate them! I now know what NOT to do. Thanks for the information.
- Shanna (age 45)
A:
Shanna- Thanks for the note. It's kind of rough to be thrown in suddenly to teach a science class. If there's any way we can help, we'd like to. For example, if some question comes up where we might be able to contribute, maybe put "Teacher needs help" at the beginning of the question, and we'll try to get to it right away.

I remember from a year when my wife taught middle school how difficult that job can be.

Mike W.

(published on 09/03/2011)

## Follow-Up #51: on science education

Q:
- Rebecca (age 40s)
Tampa, FL USA
A:
Rebecca- Thanks for this passionate contribution. It's great to hear of people engaged with the real content more than the school assignments.

Mike W.

(published on 11/19/2011)

## Follow-Up #52: edible atoms

Q:
Let's get serious here. Here's a photo of my daughter's project: brown and yellow raisins, dried cranberries, an aluminum foil ball, toothpicks, coathangers, string. http://www.facebook.com/media/set/?set=a.10150261841477713.318008.546997712&type=3&l=42037a301d
- Ellen (age 50)
Arlington, VA
A:
Ellen- I appreciate that this note is significantly more polite than the anonymous one that came in at about the same time. To be somewhat repetitive, cranberries have properties that are radically, qualitatively, different from electrons or any other small objects. See above (search for "Bell") for more explanation.

Mike W.

(published on 01/31/2012)

## Follow-Up #53: against quantum mechanics

Q:
Mike W, Shut the **** UP!!!!! Nobody wants 2 hear what u have to say!!!! Just shut up u complicated a**hole!! Can't u see u just confuse everybody more?!?!?! SHUT THE **** UP u son of a B*TCH!!!
- Anonymous (age ?)
???
A:
Unfortunately the constraints of posting on a university site required that your comments be slightly edited. Nevertheless I believe most readers will still be able to grasp the general drift of your feelings.

Mike W.

(published on 02/01/2012)

## Follow-Up #54: Bohr for the masses

Q:
This article discusses the same topic as the atom model disagreements here. http://blogs.scientificamerican.com/cocktail-party-physics/2012/02/09/dont-be-dissin-the-bohr-model/ What is your opinion? Can't we all just get along?
- Marc (age 31)
Urbana, IL, USA
A:
Good question. We don't know whether it's a good idea to teach the Bohr model on the way to learning quantum mechanics or whether it clogs up the mental pathways.We're committed to trying to get things right on this site, so even if that model were a good intermediate teaching step, we wouldn't be presenting it here. As for the article you cited, it is written from the perspective of a non-scientist who doesn't quite fully acknowledge how wrong the Bohr model is both in principle and for most practical calculations.

Your last question is of course the most important one in general. We can at least hope.

Mike W.

(published on 02/10/2012)

## Follow-Up #55: atoms in quantum field theory

Q:
My teacher made it clear the Bohr model was a useful intuitive model, but was only a historical stepping stone to a more complete understanding. She strongly encouraged us to also learn in what ways it is wrong. Your article is helpful, but my dad and I are still trying to figure this stuff out. May dad tried to explain some parts of quantum mechanics and field theory without math using some popular science books we got from the library, but it is only more confusing. Can you help? ((1)) Quantum particle question: So if we could measure the charge distribution of a helium atom, it sounds like it would show the electrons are spread around. It is also said electrons are indistinguishable. But my dad said (from a book) the electrons don't move as if they feel this entire charge distribution. They only feel the charge from the nucleus and the _other_ electron. But that seems to say the electrons can distinguish which charge distribution is due to which electron!? Yet to drive home that the electrons are indistinguishable, another book mentioned it is possible to actually write the quantum mechanics without artificially labeling the electrons and instead just using the overall charge density. But then this seems to mean the electrons would _have_ to feel the entire charge distribution, or how else would that work? Is the charge spread out around the atom or not? ((2)) Quantum field question: It sounds like the vacuum is actually full of electrons and positrons popping in and out of existence. If N_e is the number of electrons and N_p is the number of positrons, then since they pop out in pairs, can we at least say for certain that in a hydrogen atom Ne-Np = 1? But is the question 'How many electrons are in a hydrogen atom?' or 'How many positrons are in a hydrogen atom?' actually undefined according to the quantum field theory because the state includes with non-zero probability any number of electrons or positrons due to all these particles popping in and out of the vacuum? ((3)) Is there a name for the model of atoms that is the current physics understanding? Is it this quantum field model? That's what the books seem to say. Or would you teach it some other way?
- Nick (age 12)
Houston, Tx
A:
Nick- Let me take those questions in reverse order.

3. Yes, quantum field theory (specifically quantum electrodynamics, for the most part) provides the current understanding of atoms. No, we usually just teach non-relativistic pictures (the Schroedinger equation) to start with. Unlike the Bohr model, the Schroedinger picture captures a great deal of the real properties of the quantum world. We aren't fanatics about always teaching everything at the highest level of current understanding, which would be impossible for many reasons, including gaps in our own knowledge. What we try to teach are models with broad domains of applicability. Newtonian mechanics is a good example. Non-relativistic quantum mechanics works well for most problems in which the relevant energies are small compared to the rest energies of the particles. The binding energies in small atoms are small compared to the electron rest energy.

2. The H atom is indeed in a state with a definite value for Ne-Np. This state does not quite have a definite value for either number separately, just as you say. Again, however, given the rest mass of the electron, it's not a bad approximation at all to simply say Ne=1, Np = 0.
Despite the way we often talk, in any state with definite energy nothing is popping in or out. In a state with definite energy, nothing at all physical is happening, just abstract rotation of a quantum phase.

1. This one is tough without math. We've written a tiny bit about it before: .  When one writes the energy expression (Hamiltonian operator) in terms of the creation and annihilation operators for electrons one finds that there's no single-electron self-repulsion, without having to put in any explicit labeling of the electrons.

Mike W.

(published on 02/28/2012)

## Follow-Up #56: relativistic atoms

Q:
- Haley (age 14)
Jensen, OH
A:
Haley- it sounds like you could use this information soon, so that's why I'm posting this place-holder answer. I don't know enough atomic physics to answer your question with the level of confidence we try to reach on this site.

In heavy atoms like uranium the electron energies become large enough for relativistic effects to become important. Spin-orbit coupling, for example, becomes large. However, I think (with not much confidence) the the spread in the expected number of electrons around the expectation value (i.e. the intensity of the cloud of virtual electron-positron pairs) remains very small.  I'll have to check that with somebody more knowledgeable.

Mike W.

(published on 03/02/2012)

## Follow-Up #57: more on relativistic atoms

Q:
- Haley (age 14)
Jensen, OH
A:

Hi Haley- Yes, our question reader deletes all sorts of control characters, I think as a precaution against malware. It often leads to hassles for formatted inputs.

The Lamb shift does indeed come from photon effects, the quantization of the electromagnetic field. You can think of this as coming from a vacuum cloud of photon possibilities. The reason those effects are measurable rather directly in atoms but not the effects from the background cloud of electron-positron pairs is that the electron-positron pair has significant rest mass. It's not cheap to create a pair, unlike photons which have no rest mass.

Just to try to find something I know that's dimly related to your question, the electron-positron pair creation does become prominent when a heavy nucleus is bare, stripped of electrons. Then its electric field is so big that it causes sparking of the vacuum- pulling electrons out of nothing and spitting out positrons. That quickly reduces the field and the process stops. In an atom, the electrons are already present, suppressing such effects.

Mike W.

p.s. I finally remembered to get some help from a colleague on this. The positron density even in uranium is "very low". The reason is that it costs so much energy (1 MeV) to make an electron-positron pair. My colleague (Eduardo Fradkin) say that the math for calculating the positron density is similar to the math for calculating the carrier density in an intrinsic semiconductor, with that 1 MeV playing a role similar to the band gap. The concentration of positrons falls off exponentially with the size of that gap. He says it's much less than 1% even for uranium. For higher atomic numbers the field gets larger near the nucleus and the energy scale goes up , so you start getting the sparking we described above, and actually make real electron-photon pairs.

(published on 03/03/2012)

## Follow-Up #58: malicious atom models

Q:
Would it be a good idea to use the concept of malicious compliance to complete the atom model assignment? All That is required is a nucleus model including an appropriate number of good sized balls of two different colors. Perhaps the teacher won't understand so include a note that points out that the nucleus is about 99.97% of the atom's mass. If over 99% isn't good enough the student can point out that you can't tell were the electrons are, they are vanishingly small even at this scale, and that since the size of an atom is about 18,000 times the size of the nucleus the electrons are probably miles away right now. Richard Feynman, who had a gift for explanation of complex subjects, pointed out that "If an apple was magnified to the size of the Earth, then the atoms in the apple would be approximately the size of the original apple." Yes I have been in trouble for most of my life for my attitude.
- Tim Weber (age 63)
Lomita, CA
A:

Whoops, this slipped between the cracks some time ago. It's a relief to see readers with even worse attitudes than ourr own. Needless to say, this approach would be risky to a student's grade.

Mike W.

(published on 04/26/2012)

## Follow-Up #59: a student's perspective on atom models

Q:
- Audrey (age 13)
Texas
A:

Your note helps remind us of how things look from a student's perspective.

Thanks,

Mike W.

(published on 10/10/2012)

## Follow-Up #60: What do electrons really do?

Q:
- Mary (age 53)
Bay Village, OH
A:
Mary- Thanks, it's great to see someone following this discussion and heading right for the core issues.

I just gave a talk that sort of addresses (I can't claim it answers) your questions. The slides are posted, and the actual video should be available fairly soon.

On the Bohr model, now that you mention it, it's actually more wrong than saying the sun orbits the earth. In general relativity there are legitimate, although awkward, reference frames in which the earth stands still. These make no false predictions. The Bohr model makes a number of false predictions starting with the prediction that the minimum orbital angular momentum is h/2π, rather than the actual value of zero.

There are certainly some people (e.g David Deutsch) who claim to fully understand all the issues of quantum mechanics. Most of us believe mysteries remain. Here's a little bit of the part of the story we think we understand.  There's a wave-like equation, saying how the quantum state for a collection of things changes as a function of time. It seems like things always stay in a wave-like quantum state. However, parts of that state come to represent really different outcomes- a live cat or a dead cat in the classic example. Up to that point, we really do understand things (we think) just by taking the wave-like math seriously as a representation of the only ingredients of reality. Next, however, we never see more than one of those different outcomes. There are several radically different "interpretations" of why that is, and why the probability rule for seeing each of the different outcomes looks the way it does.

Mike W.

(published on 03/02/2013)

## Follow-Up #61: model of modern quantum theory of atom

Q:
okay, i'm also trying to build an atom model but this year my teacher said we can now only do the modern theory or quantum theory.. any help? oh and Mike W, do you like own this website because your the one answering all these questions. I pose no offense, just wondering.
- Ariana P (age 14)
California
A:
Hi Ariana- It might be a good idea to ask your teacher what he or she meant by  "the modern theory or quantum theory". If they mean something like the actual theory now used, then the electron state would be represented by a sort of fuzzy cloud, maybe made of a cotton ball. You might represent the possibility of the electron then showing up in smaller regions by some sort of sparkly thing embedded in the cotton. It's possible, however, that your teacher meant something else, perhaps one of the theories that were used before 1925.

Mike W.

p.s. The Physics Department at the University of Illinois "owns" this site, but Lee and I do most of the answering and are responsible for the current content.

(published on 03/27/2013)

## Follow-Up #62: tips on atom models

Q:
Thought the kid's looking to make a 3D model needed some help so here I go! Take I 3 inch Styrofoam ball roll it in THIN glue. Use two different colored SMALL pompoms (craft store) AND ADD THE CORRECT AMOUNT USING ONE COLOR FOR PROTONS, DIFFERENT COLOR FOR NUETRONS. you nucleus is done. connect pipe cleaners in a circular fashion and glue different colored electrons for each "shell". Each shell "circle" can be attached by a thin piece of wire. push conneting wire or additional pipe cleaner into the nucleus to attach. I have helped the kids with plenty of these, Relatively inexpensive to make and not difficult.
- debra (age 53)
michigan
A:
I can't say I like it, but kids have to get through school somehow.

Mike W.

(published on 04/15/2013)

## Follow-Up #63: looking back on atom models

Q:
I just finished reading through all of these follow-ups. Nearly three years of talk, that's cool. As a middle school student who seems to old for my age, I can honestly say that you've been a great help to me and everyone who has accepted it, Mike W. I'm here doing an atom model project now, and it was only when I found this site that I realized what I was doing was perhaps off, but other people's responses have disappointed me. I'm glad to see the fair arguments against you(which you have responded in kind), but some of these others. I don't think any one person deserves that type of "hate", especially when he's only trying to help. I'm only speaking what my mind is spewing right now, but Mike W, you've been a great help. I wonder if someday we kids WILL be taught the correct things?
- John (age 13)
Texas
A:

John- Thanks for your kind note. It's alwauys encouraging to hear that some of the old answers are still being read with real interest.

The atom model question is just one little piece, not the most important one, of the whole issue of how best to teach science and math. My wife teaches a massive elementary statistics course, perhaps the most important technical topic for most people who aren't going on in specialized fields. There's a dispute there between teaching a big set of formulas and teaching somewhat less but with more thorough understanding. It's an interesting case, because, unlike the quantum atom, the deeper way of teaching doesn't rely on students having special preparation.  She's on the side of understanding, which turns out to be popular with most students, but is not the way of most statistics teachers.

Mike W.

(published on 11/29/2013)

## Follow-Up #64: Is answering physics questions boring?

Q:
Wow...you've been at this a long time mike. Do you really enjoy it? It's kind of a boring job. Anyway, I'm doing a project and have found this q and a site super helpful.
- Anonymous (age 13)
America
A:

Lee and I and the other volunteers here aren't paid. So we only answer what we want when we want. So it seems we do enjoy it.

We're delighted that you found it useful. That adds to the enjoyment.

Mike W.

(published on 12/01/2014)

## Follow-Up #65: atomic weirdness?

Q:
Wow, everyone was really going after each other XDWhat's even weirder is that it started almost 7 years ago!
Texas, US
A:

Let's blame it on the atoms. They started the weirdness.

Mike W.

(published on 10/31/2015)

## Follow-Up #66: model of strontium

Q:
Hi Dr. Van, I really enjoyed the questions so far and your explanations. I have a middle school student with the same project. Like one the previous comments, I immediately started talking with her about the electron cloud, shells, etc. We even talked about doing boron since that is the first that breaks the spherical symmetry. My plan was to use jelly or colored ice for the clouds. We need something with structure and that is transparent (somewhat). However, the teacher give out point based on the atomic number. To get an A, she needs to do at least Strontium. Without having to ask favors of folks with 3 D printers, any suggestions on how to actually make a physical model?
Maryland
A:

Wow, that's not easy. I guess you can put 38 sparkles into some sort of gel. That captures some of the flavor, but not the structure of those wave functions. Even with a 3-D printer, those overlapping states aren't so easy. Printers don't do negative ψ!

It's interesting that strontium was picked as the one to do. Since it's got filled shells the overall state is spherically symmetric. I wonder if the teacher would accept that overall symmetry and allow a spherical model?

Mike W.

(published on 11/02/2015)

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