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Quantum Chemistry or Quantum Physics?

  1. Jun 17, 2008 #1
    I was wondering if someone could tell me what exactly is the difference between Quantum Chemistry and Quantum Physics? Whenever I look in a Chemistry textbook, I see Quantum Chemistry and the latter is true for Physics - yet strangely enough I see most of the information is quite similar. Although maybe I have never delved deeply enough into the texts to be able to see the difference.

    So is there any big difference or do the two fields just approach the topic of Quantum theory differently?
  2. jcsd
  3. Jun 17, 2008 #2
    Well quantum chemistry and quantum physics definetly overlap but a quantum chemistry book will most likely be less theoretical and less concerned with mathematical rigour and more concerned with 'real world' applications and such. And might for example spend a lot more time talking about the zeeman effect and NMR where a quantum physics book might spend more time talking about rigged hilbert space and operator theory
  4. Jun 17, 2008 #3
    Oh I see, that makes sense. Would you say that someone studying chemistry (specifically Biotechnology/Biochemistry) could benefit with some study of the Physics of such topics, or is this more of a waste of time?
  5. Jun 17, 2008 #4
    I'd say it's a waste of time. Physicists always complain about the lack of rigour (and the lack of a strong theoretical framework) in things like bio (and mathematicians complain about lack or rigour in physics) but the truth is bio students don't learn physical theory (and instead are often taught incorrect but ultimately 'good enough' rules of thumb and such) because it takes a long time to teach it and there are few fields of bio where it will ever come up.
  6. Jun 17, 2008 #5
    That being said, I still reserve the right to scoff at things like drawing a lipid bilayer as a bunch of balls with squigly tails and saying 'like the squigly line hates water and like the ball likes it'. :)

  7. Jun 17, 2008 #6

    Tom Mattson

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    I've taken both quantum chemistry and quantum physics. Both started out with basic wave mechanics, but then the chem course focused on atoms and molecules while the physics course went into the dirac formalism, time evolution, angular momentum, symmetry, and scattering. Both courses contained perturbation theory and the variational method.
  8. Jun 17, 2008 #7
    Tom thanks for the input, now I can generally see that Quantum Physics is something more of what I would like to study.
  9. Jun 17, 2008 #8
    Really? The quantum chem course didn't teach Bra-Ket notation?
  10. Jun 18, 2008 #9
    maverick_starstrider: Dear Sir, I must object to the notion that biochemists doesn't need QC or QM.

    It is actually very useful and explains such random things like why lykopene is red/orange and stuff like that.

    For the more hardcore stuff, it's very useful for the pharmaceutical industry and calculations on bio-molecules that tend to be very big.

    Biocore: I think you should take a QC course. You will find it useful.
  11. Jun 18, 2008 #10
    ...I had that stuff in my first year general physics course. o_O

    You may not need quantum physics, but quantum chemistry (or physical chemistry as it's sometimes labeled) should be a strong consideration for anyone in a chemical program if it's not already required. You can add the QM physics courses later (or earlier) if you have a strong interest.
  12. Jun 19, 2008 #11
    Quantum chemistry is applying quantum mechanics to chemical problems. Quantum physics gives you the whole story in a more mathematical form. I'd say study some quantum chemistry if you're in bio, and even that is over kill. Doing quantum physics is over over kill, and most of it you won't find very useful because it is highly abstract and not very practical. So chemists devised their own spin where you study only the stuff needed for chemistry.

    As an analogy, do you need the foundations of language and linguistics to read and write english? Certainly not. Neither do you need quantum mechanics to be working with atoms. Ofcourse, every bit helps if you really want to change the world. But that should be studied independently, and not as something to deter you from your main goal - biology.
  13. Jun 19, 2008 #12
    Some of it, which is why they traditionally bother with things like Greek and Latin roots.
  14. Jun 19, 2008 #13


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    chemistry is just a big sub-branch of physics.. atoms and molecules etc. :approve:
  15. Jun 19, 2008 #14


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    Thats strange because English is a Germanic language.

    To the OP. Both courses will be similar. You obviously need a foundation in quantum mechanics before you can apply it to anything so that will most likely be exactly the same as a lower undergrad physics course. Where things will chage however is that quantum chemistry will remain focused on applications (i.e. molecular quantum mechanics) physics classes will move on to QCD and QFT and perhaps re-introduce the subject in terms of a more modern derivation along the lines of Sakurai's book rather than the historical approach.
  16. Jun 19, 2008 #15
    have you considered Quantum Quantum?
  17. Jun 19, 2008 #16
    Wrong. Most of chemistry makes no refrence to physics. Atoms were known to exist before any quantum mechanics were used to describe them. Reactions were studied by measuring relative masses of different compounds, and crystals were used to deduce structures. In fact, that is how most of chemistry is continued to be studied.

    Physical chemistry is a sub-branch of physics. This is where we deal with physical notions of thermodynamics and electricity, and study the motion of molecules via quantum theory. Using your logic, biology is a sub-branch of chemistry (pfft, atoms and enzymes) and physics is a sub-branch of math(pfft equations and numbers). Physicists known squat about chemistry.
    Last edited: Jun 19, 2008
  18. Jun 19, 2008 #17


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    Still took a physicist to sort out the periodic table of elements for you. :tongue:
  19. Jun 19, 2008 #18
    Chemists need to leave trivial stuff to physicists to make them feel important.
  20. Jun 19, 2008 #19
    Dont forget that math is just a sub branch of philosophy (pfft just logic and crap)
  21. Jun 20, 2008 #20


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    i) Chemistry is a sub-branch of physics in that sense that chemistry deals with the electromagnetic force. All atoms and molecules etc. are interacting due to this force, and every reaction in chemistry can in principle be formulated as interactions on electrodynamical basis. Chemistry has, however, developed more efficient methods to deal with many of these reactions. A chemical reaction is just electrons chaning configuration in energy-space.

    This is from wikipedia:
    "Chemistry (from Egyptian kēme (chem), meaning "earth"[1]) is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.[2] Historically, modern chemistry evolved out of alchemy following the chemical revolution (1773). Chemistry is a physical science related to studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination, which incorporates the concepts of energy and entropy in relation to the spontaneity of chemical processes.

    Disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the energy related studies of chemical systems at macro, molecular and submolecular scales; analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system (see subdisciplines)."

    Measuring the mass of something, isn't mass a physical quantity?... ;-)

    ii) Physics is not a sub-branch of math, math is the language of physics. Physics deal with the real world, physics is also an experimental science. Math is just constructing a coherent logical 'language' to describe and relate quantities.

    So saying physics is a subbranch of math, is like saying that politics is just a subbranch of English..
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