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In High School chem wrong like HS Physics?

by KingNothing
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KingNothing
#1
Nov30-04, 12:01 AM
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When I took physics in high school, it was prett fun partly because of the fact that there were better theories and that mainly what we were learnign was ultimately wrong.

I'm in honors chemistry now, and the class isn't giving me any trouble, however I would absolutely love it if I could come up with a few examples and/or theories that would sort of disprove what we are learning. From what we've learned (we are studying electron configurations now, atomic radii and we represent energy levels as rings around a nucleus) what we are studying is basically "classic" model of molecules. Is there anything I can bring up in class that generally is more accurate than our classic models? (i.e. relativity in physics when studying newtonian mechanics)
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Loren Booda
#2
Nov30-04, 12:33 AM
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Beyond the valence model is the more accurate, but harder to visualize electron cloud probability model. The latter gives a continuously changing picture of probabilities, based on quantum mechanics, that electrons would occupy spatial points around a given nucleus. Demonstrating it, though, can often be like trying to map the positions of condensation within a three-dimensional weather cloud on a two-dimensional page.
Gokul43201
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Nov30-04, 12:39 AM
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Ah, so you want to one-up your teacher, eh ?

You are only being taught something that's roughly equivalent to the Bohr model for the atom. According to what you're learning, levels (or shells) of higher energy are farther away from the nucleus. So, it would seem to make sense that all the electrons in the n=4 shell have more energy than those in the n=3 shell. But this is not true. So, in fact, there are some electrons in the 3rd shell that are at a higher energy the some of the electrons in the 4th. Within shells, there are things called orbitals, and these orbitals have different shapes.

For a more accurate understanding of the behavior of electrons in an atom, one must solve what is known as the Schrodinger Equation (which is a technique of Quantum Mechanics). But really, the Bohr model does surprisingly well for things like atomic spectra.

gravenewworld
#4
Nov30-04, 01:05 AM
P: 1,405
In High School chem wrong like HS Physics?

In HS all you need is the Bohr model, it should work just fine. Although solving the Schrodinger equation will tell you everything there is to know about that system, it can only be solved for the hydrogen and hydrogen like atoms nothing more. There are still over 100 elements left that the Schrodinger equation must be solved for. The electronic congifigurations you are learning 1s2 2s2 etc... are merely approximations since the schrodinger equation can not be solved for an atom with more than 1 electron.
so-crates
#5
Nov30-04, 04:11 AM
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Its not really that major, but Hund's rule fails for the Lanthanides and Actinides, due to complications in the electron picture described by previous posters. In other words, the configuration for Cerium (atomic # 58) is [Xe] 4f1 5d1 6s2 and not [Xe] 5d2 6s2 as one might expect - the 4f1 electron is a lower energy state than the 5d2 electron.

There are many exceptions to the octet rule - particularly with sulfur and phosphorus. And it doesn't really make much sense metal compounds (alloys)
ZapperZ
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Nov30-04, 06:36 AM
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Quote Quote by KingNothing
When I took physics in high school, it was prett fun partly because of the fact that there were better theories and that mainly what we were learnign was ultimately wrong.

I'm in honors chemistry now, and the class isn't giving me any trouble, however I would absolutely love it if I could come up with a few examples and/or theories that would sort of disprove what we are learning. From what we've learned (we are studying electron configurations now, atomic radii and we represent energy levels as rings around a nucleus) what we are studying is basically "classic" model of molecules. Is there anything I can bring up in class that generally is more accurate than our classic models? (i.e. relativity in physics when studying newtonian mechanics)
I want to emphasize that, if what you meant by "wrong" is the newtonian mechanics, then you are incorrect. If you think newtonian mechanics are wrong, then you should quickly evacuate the building you are in, because it was constructed by structural engineers who used newtonian mechanics.

Let's get this very clear: Newtonian mechanics is NOT wrong. It just has a region of applicability. We know when we can safely use it, and we know when we can't. In fact, anyone who thinks we should use SR or QM to construct a house is a menace to society and should be quickly institutionalized.

Zz.
altered-gravity
#7
Nov30-04, 02:02 PM
P: 62
Quote Quote by KingNothing
I'm in honors chemistry now, and the class isn't giving me any trouble, however I would absolutely love it if I could come up with a few examples and/or theories that would sort of disprove what we are learning. From what we've learned (we are studying electron configurations now, atomic radii and we represent energy levels as rings around a nucleus) what we are studying is basically "classic" model of molecules. Is there anything I can bring up in class that generally is more accurate than our classic models? (i.e. relativity in physics when studying newtonian mechanics)
Be patient, those models you are studying now are inaccurate but will help you to understand "pure quantum" chemistry methods. Anyway, if you canīt stop your curiosity, congratulatins!. I recommend you Ira Levineīs Quantum Chemistry (with another book of introduction to QM that you choose). Wellcome!
KingNothing
#8
Nov30-04, 08:13 PM
P: 949
Quote Quote by ZapperZ
I want to emphasize that, if what you meant by "wrong" is the newtonian mechanics, then you are incorrect. If you think newtonian mechanics are wrong, then you should quickly evacuate the building you are in, because it was constructed by structural engineers who used newtonian mechanics.

Let's get this very clear: Newtonian mechanics is NOT wrong. It just has a region of applicability. We know when we can safely use it, and we know when we can't. In fact, anyone who thinks we should use SR or QM to construct a house is a menace to society and should be quickly institutionalized.

Zz.
Yes, yes, I'm aware that it's 'less accurate' a.k.a. 'region of applicability' a.k.a. 'region of wrongness'...however you want to say it. I know that even less accurate theories have their place. I knew that before. Sorry if you were mislead by the title.

Anyway, back to chemistry. We talked in class about ionization energy, reactivity, and atomic radiuses and how they relate to the electron configuration. Like for example, my teacher explained that elements' ionization energy varies with the atomic radius because if the radius is greater, then the valence electrons are farther from the nucleus and thus require less power to be pulled away...or something to that effect. How would something like that be explained with quantum mechanics?

In my head I'm kinda thinking about how to convert the Bohr model to QM model, and so far I just kinda take electrons and throw them in a big cloud where they move around like minnows in a bucket...but how do I incorporate something like a valence shell or an atomic radius?
Gokul43201
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Dec1-04, 12:11 AM
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You can't try to understand QM at this level. Just be patient and you'll learn some of in it college.
Jimm
#10
Dec1-04, 02:08 AM
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wait until uni / college and it really all becomes clear........
GCT
#11
Dec1-04, 07:51 PM
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Study the shapes of the suborbitals, their orientations, size, and distance from the nucleus, these are somewhat related to the positional probability and you can more skillfully understand such concepts as you mentioned. This will be more applicable when you enter organic chemistry (which hybrid orbital sp3, sp2, sp, offers more stability for its anion, using the factors I mentioned in the beginning of this post? etc.......)
pack_rat2
#12
Dec1-04, 11:18 PM
P: 183
Quote Quote by KingNothing
When I took physics in high school, it was prett fun partly because of the fact that there were better theories and that mainly what we were learnign was ultimately wrong....
I'm curious about what you studied in physics that was wrong. If it really was, then teachers, parents and students need to raise a stink with the company that publishes that text, and the school for adopting it.
Loren Booda
#13
Dec2-04, 10:47 AM
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Even some leading philosophers have contended that all theories are ultimately wrong.
Up_Creek
#14
Dec2-04, 02:05 PM
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If/when someone disproves the theory of atoms/molecules ect i'll be there to laugh. But then i'll probably stop, since it would ultimately ruin the world. Can you imagine what it would be like if that happened? Almost everything we know would be wrong...

That would be a bit of a trip heh

Jordan Veale


With the sad state of affairs in the world today, maybe it would be best of some people learned they were wrong all along...
ZapperZ
#15
Dec2-04, 02:32 PM
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Quote Quote by Loren Booda
Even some leading philosophers have contended that all theories are ultimately wrong.
.... and yet you (and them) do not see the irony in THAT theory.

Zz.
Loren Booda
#16
Dec2-04, 06:16 PM
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ZapperZ,

I said it was a contention, not a theory. I also mentioned that this is true ultimately, not necessarily now. No doubt our statements, like any other, are vulnerable to paradox in their finiteness. I'm sorry to have steered off onto the path to philosophy.
Loren Booda
#17
Dec2-04, 06:23 PM
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Up_Creek,

There are realists, among them Bas C. van Fraassen I believe, who propound that atoms are theoretical, not real, entities, because they are not directly observable. I'm no expert in the subject, though.
ZapperZ
#18
Dec2-04, 08:15 PM
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Quote Quote by Loren Booda
Up_Creek,

There are realists, among them Bas C. van Fraassen I believe, who propound that atoms are theoretical, not real, entities, because they are not directly observable. I'm no expert in the subject, though.
Man! You weren't kidding when you said "No doubt our statements, like any other, are vulnerable to paradox in their finiteness.". Right after you felt sorry for "steering" this thread into philosophy, you immediately turn around and contradict yourself.

$10 says that this "Bas C. van Fraassen" has never done a single experimental physics measurement on an "atom". And yet, he has managed to sucker enough people to actually pay MORE attention to his ignorant statements than what ALL of physics has to say.

Zz.


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