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darnoconrad

Chemistry: Quantum Atomic Model for Atoms

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Hello,

I am starting to study Chemistry and have come across a hump. The book I am learning from uses a Quantum Mechanical Model to describe atoms... Is it necessary to learn this in order to understand chemistry? or should I be looking for a new book to learn from?

The author of the book does not even give a good reason why they use this.

"Early models of the atom had electrons going around the nucleus in a random fashion. But as scientists discovered more about the atom, they found that this representation probably wasn't accurate."

... And Ayn was probably right...

Please help! I am eager to learn but do not want to get stuck on this point. Please tell me if I should learn it and move on or find a better book so that I can be firmly grounded in the beginning of my studies.

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If it helps to ease your pressure, how much you need to learn about quantum mechanics (or anything else) for chemistry depends a lot on what you will specialize in:

Organic Chemists function get by just fine by memorizing piles and piles of information about how different functional groups like to interact, and it's amazing how far that kind of information can get them without even needing to understand much QM at all.

Inorganic Chemistry may involve more abstraction, mathematics, and more involvement of QM concepts. Advanced Inorganic Chemistry may get pretty mathy, where you do some serious QM paper and pencil problems, or use symmetry theory to estimate what the molecular orbitals in some molecule could look like.

Solid State Chemistry requires a good understanding of crystallography.

Analytical Chemistry needs some qualitative (and maybe quantitative) understanding of the physics concepts underlying a particular instrument. For example, if it's an NMR you should probably learn a little about nuclear spin-states and about how currents can be excited in the electron cloud which can shield the nucleus from applied magnetic fields. If you are doing Microwave spectroscopy you should probably learn about the application of QM to study rotational states in small molecules.

I'm giving you this information not to overwhelm you but to show how varied chemistry is. Chemistry is a big wide world and there's something for everybody depending on their skills and interests. For people who do lots of synthesis work in the lab (especially organic synthesis) what's most important is that they develop a good chemical intuition, which comes more from memorizing information and working in the lab than from QM.

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I am starting to study Chemistry and have come across a hump. The book I am learning from uses a Quantum Mechanical Model to describe atoms... Is it necessary to learn this in order to understand chemistry? or should I be looking for a new book to learn from?

There are some genuinely bad textbooks out there, and you need to be assertive in finding good materials to learn from if those provided by your instructors are lacking. In the modern university, especially in science programs, you cannot just trust that your professors will choose the right books and teach the courses in the right way to foster learning. Learning the material will probably take a considerable independent effort.
The author of the book does not even give a good reason why they use this.

"Early models of the atom had electrons going around the nucleus in a random fashion. But as scientists discovered more about the atom, they found that this representation probably wasn't accurate."

There are much better books to be found than "Chemistry Essentials for Dummies". By trying to dumb down the material to make it easier for the reader to understand, all the book is actually doing is presenting concepts in vague ways that are totally incomprehensible for learning.

When I needed to start learning chemistry what I found very valuable was older chemistry texts (from the 60's, 70's, etc).

Please help! I am eager to learn but do not want to get stuck on this point. Please tell me if I should learn it and move on or find a better book so that I can be firmly grounded in the beginning of my studies.

What stage are you in your studies?

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When I needed to learn chemistry what I found most useful in the beginning was learning simple experimental things, like what is the formal definition of the ionization potential (also known as ionization energy) and how does it change as you move across a row or move down a column in the periodic table? Understanding this and the electron affinity (and how it changes across the periodic table) are crucial for developing the concept of electronegativity.

But at the end of the day learning some concepts about Quantum Mechanics is necessary. You need to understand what orbitals are, how electrons fill the orbitals, how atomic orbitals mix to form molecular orbitals, etc. Those basic concepts are crucial, and can be grasped without much math at all.

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The author of the book does not even give a good reason why they use this.

"Early models of the atom had electrons going around the nucleus in a random fashion. But as scientists discovered more about the atom, they found that this representation probably wasn't accurate."

Quantum Mechanics was needed because classical physics theory failed spectacularly when things moved to the atomic level.

For example, classical physics could not account for the discrete spectrum of energies that atoms displayed. In an atom, an electron orbiting the nucleus isn't allowed to take on any energy and any trajectory in the same sense that a planet orbiting a star can. Instead the energy is quantized and the electron's location is confined to orbitals. The reason for this is purely quantum mechanical, and can be formally derived by working out the math for the hydrogen atom. For practical purposes in Chemistry it won't be necessary to delve into the math of this; instead what is important is that you get a firm qualitative grasp of the relevant concepts.

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A good, free, internet resource that may be helpful for you is hyperphysics:

For example, here is a concept tree of chemistry:

http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/chemcon.html (you can click the bubbles to take off down different branches)

Here is one for quantum mechanics:

http://hyperphysics.phy-astr.gsu.edu/hbase/quacon.html#quacon

Under "Failures of Classical Physics" they provide a nice discussion of why the quantum theory was needed

http://hyperphysics.phy-astr.gsu.edu/hbase/qapp.html#c3

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I am starting to study Chemistry and have come across a hump. The book I am learning from uses a Quantum Mechanical Model to describe atoms... Is it necessary to learn this in order to understand chemistry? or should I be looking for a new book to learn from? ...

Please help! I am eager to learn but do not want to get stuck on this point. Please tell me if I should learn it and move on or find a better book so that I can be firmly grounded in the beginning of my studies.

It's not clear how you wound up with a chemistry book to "start" a study of chemistry which requires quantum mechanics as a prerequisite in order to "use" it. Did you pick the book? Are you missing background knowledge required to read the book, or does the book only purport to require a very elementary, beginning concept of quantum mechanics which is included in the book? Is your problem with the book a missing background, or only that you don't sufficiently understand an introduction to quantum mechanics included in the book you have?

Yes, quantum mechanics is required to understand the atom and chemical bonds, and a lot more, but not everything in chemistry. Where it is required it cannot be bypassed pedagogically and you should not try to avoid it.

You do not, however, require a full course in quantum mechanics as a prerequisite if you are only beginning to learn some elementary concepts of chemistry. Unless you already have a background in math and physics that far exceeds the level of your current beginning knowledge of chemistry, it would not be possible for you to jump into a full quantum mechanics course/book at this time because it is too advanced in the hierarchy of knowledge which you are not far enough into yet. You would not yet be able to understand quantum mechanics at that level.

In almost any course you learn (self-taught or not) it is very useful to use more than one book in order to obtain insights into the material from different perspectives, depths, and scopes than are included in a single text. This may solve your problem.

The Linus Pauling text re-issued as a Dover paperback cited by Carlos is a classic and is one reference you should have if you are serious about the subject (I wish I had known to use it), but it's impossible to tell from your description if it would help you at the level of understanding you currently have and are trying to achieve from whatever the book is that you are using.

Another supplemental book you could consider is another older one, which I used as a college freshman, Fundamental Chemistry by Andrews and Kokes. It is now out of print and you can buy a used copy very inexpensively. It begins with elementary quantum mechanics at the level required to understand the basic principles of chemical bonding and the structure of the periodic table of the elements, and would probably be worth having if only for most of those first half dozen or so chapters to supplement whatever else you have.

But you should realize that no account of quantum mechanics and the associated physics at that introductory level will be able to satisfy the kind of understanding and "firm grounding" that you want. It will only be introductory, referring to results whose reasons you would not yet be able to fully understand, but it will introduce you to important scientific principles (as opposed to dogma handed down) and serve as a motivation to learn more later when you can, leaving you for now with a lot of unanswered questions of where the elementary quantum mechanics you begin with comes from. Always keep in mind the hierarchy of knowledge -- with what depends on what, how you know what you have learned so far, and what gaps you need to fill in later for a fuller understanding because you have only been told of certain results without the detailed reasons for them.

The alternative to dealing with such gaps in reasoning now would be an overly historical account that would leave other gaps, confusions and ambiguities along the way of your learning, and which you would still have to come back to later with even more inefficiency in the learning process. Understand what you can, keeping firmly in mind what you know and what you don't, with the goal of revisiting it all later with both more detailed and advanced accounts and the historical development to fully understand how it was all put together over time and what the justifications are in the hierarchy of dependencies. That is what will ultimately give you the "firm grounding" you require. The science you are trying to understand has been a very complex and convoluted progression over a long period of time, and there is no simple, deductive way to learn it in a "straight line".

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Hi guys,

Thanks for the replies.

I'm just starting from scratch and my mathematics is not that strong(which I've learned on my own as well). I failed math and science in high school but now am 10 years later and want to learn and see if I can make a career out of it. I am trying to learn on my own, at least the basics, before enrolling into a university course/program. I figure this will give me at least some kind of advantage when I try to enroll.

Which kind of chemistry? I don't particularly know. I will see which one I can understand before pinning myself down.

You got it Carlos, I've purchased Chem for Dummies, I didn't know where else to start. Now I've ordered the Linus Pauling book.(thanks ewv)

The reason I asked about the quantum mechanical model is because it kind of sounds to me like an answer when no better answer is available; kind of like Copernicus' Epicycles. Copernicus figured it was the sun at the center of the solar system but still could't account for all the movements of the planets, so he devised complicated models in order to attempt the describe the motions of the planets. However I am willing to bite the bullet as it seems there's no way around, at least at the current level of understanding of chemistry.

Learning math throughout my childhood was difficult and I think I know why. 1. I was in French Immersion, and math was in french when my primary language was english(no wonder none of my peers developed careers outside the humanities) 2. Lack of respect for hierarchy in high school. 3. Teachers never giving concrete examples of how it applies to reality, everything seemed like a floating abstraction.

Learning Objectivism, for me, was the easiest thing I've ever done (when I was age 23). I am very confident in my own ability to integrate and find that this is what gives me the most joy. My goal in pursuing chemistry is to develop a fundamental understanding of math and science and use that knowledge specifically in chemistry in order to develop new advances in the field. I don't look only to applying what I know to repetitive tasks but I look to innovate. At this stage only time will tell if I will be able to accomplish this. However, I do believe it will be an uphill battle.

Do you guys know any Objectivist scientists in the Toronto area?

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The reason I asked about the quantum mechanical model is because it kind of sounds to me like an answer when no better answer is available; kind of like Copernicus' Epicycles. Copernicus figured it was the sun at the center of the solar system but still could't account for all the movements of the planets, so he devised complicated models in order to attempt the describe the motions of the planets. However I am willing to bite the bullet as it seems there's no way around, at least at the current level of understanding of chemistry.

Quantum electrodynamics is accurate to 12 decimal places.

Copernicus, although he was right about the earth traveling about the sun, assumed -circular orbits- for the planets. This made the Copernican theory less accurate than the Ptolemaic theory and epi-cycles had to be introduced to correct the errors.

Kepler finally got it right. He fitted elliptical orbits to Tycho Brahe's data. In particular he got the motion of Mars pretty well. No more epicycles were required. Newton complete the breakthrough that Kepler made by providing a force law to account for the motion of the planets about the sun. Newton's gravitational theory was very accurate but it failed to account for the motion of Mercury. The precession of the perihelion of Mercury was off about 43 arc seconds a century. This defect was remedied by Einstein's General Theory of Relativity which is really a theory of gravitation.

Einstein's theory was not a minor fix to Newton's theory. Einstein postulated a totally different theory of space and time (space-time, actually). Newton assumed a "flat" Euclidean geometry for space and time independent of the motion of bodies from which time intervals were measured.

Thus far Einstein's theories are the current reigning champions.

ruveyn

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ruveyn,

Awesome summary :) My question is: is the quantum mechanical model(QMM) just correcting previous inaccuracies? or is it 100% consistent with what is happening, explains everything without contradiction, and the reasons are understood?

Regardless, since from what I've read here, in order to deal with the world of chemistry I need to know the QMM. Thus, I will do learning it.

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ruveyn,

Awesome summary :) My question is: is the quantum mechanical model(QMM) just correcting previous inaccuracies?

Quantum Mechanics is a lot more than just a "model" that corrects failures of older theories. It is an entire new theory of mechanics which successfully describes and predicts atomic level phenomena. It is the foundation of any theoretical understanding of chemistry: the periodic table of the elements is periodic because of the nature of the solutions one obtains for the hydrogenic atom in QM.

For spectroscopy, QM provides the theoretical framework needed to understand what people are seeing in the laboratory when they do, for example, rotational spectroscopy or Raman scattering:

http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/rotrig.html

http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/vibrot.html

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/raman.html

QM gives us the chemical origins of ferromagnetism, or weird and interesting things like why Mercury is a silvery liquid while Gold is a golden solid.

or is it 100% consistent with what is happening, explains everything without contradiction, and the reasons are understood?

QM calculations gives us numbers which can match those of experiments very well. What QM means on a deeper level though, I'm not sure anyone really understands that at all...

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Carlos,

Thank you for your very complete answer. You don't live in Toronto do you? :) Or for that matter anyone replying to this topic so far. hehe. I think my uphill battle would be a lot easier with mentors like you.

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Right now in my infancy of the study of chemistry I believe I will be leaning toward inorganic chem as opposed to organic chem (although I read that they have a lot of overlaps).

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Carlos,

Thank you for your very complete answer. You don't live in Toronto do you? :)

Negative :(

Or for that matter anyone replying to this topic so far. hehe. I think my uphill battle would be a lot easier with mentors like you.

The mentors you need are people like Linus Pauling, Robert Mulliken, and Paul Dirac. Try to find good old books/articles/etc written by some of the older "giants" who pioneered these fields.

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Right now in my infancy of the study of chemistry I believe I will be leaning toward inorganic chem as opposed to organic chem (although I read that they have a lot of overlaps).

Be careful to constrain yourself too early on. When I started in physics I just "knew" I was interested in astrophysics and that I "hated" anything involving computers and chemistry. Now though I do computational chemical physics (also known as "quantum chemistry") and love it...

Read and immerse yourself and let your interests take you where they will.

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Be careful to constrain yourself too early on.

That was supposed to be, "Be careful NOT to constrain yourself too early on".

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ruveyn,

Awesome summary :) My question is: is the quantum mechanical model(QMM) just correcting previous inaccuracies? or is it 100% consistent with what is happening, explains everything without contradiction, and the reasons are understood?

Regardless, since from what I've read here, in order to deal with the world of chemistry I need to know the QMM. Thus, I will do learning it.

Classical mechanics and classical (non-quantum) electrodynamics is totally unable to account for the doings of atoms at a small scale. It cannot account for the spectrum of heated gasses. It cannot account for the tunneling of electrons through a potential barrier. At a small scale classical physics is an utter failure. Atoms cannot be understood, semi-conductors cannot be understood except in quantum mechanical terms.

ruveyn

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There are much better books to be found than "Chemistry Essentials for Dummies".

For example, a little perusing on amazon.com yielded this:

http://www.amazon.co...8266168&sr=8-13

I haven't read it but the book is about ten dollars and has good reviews as an undergraduate introductory text.

I'm working through this book now. On Chap 3.

Do you know if there is a Answers/Solutions for this book?

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I'm working through this book now. On Chap 3.

Good, I hope it's useful!

Do you know if there is a Answers/Solutions for this book?

Sorry I have no idea.

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