Movement of electrons in atomic orbitals

Discussion in 'Chemistry' started by Muzaffar, Jul 1, 2013.

  1. Muzaffar Registered Member

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    I've actually started AS level Chemistry and I think I lack an understanding of this basic concept.
    This is what I know:-

    Orbitals are regions where there is high probability of finding an electron.
    's' orbitals have a spherical shape and 'p' have a dumbbell one.
    But how do electrons move within the orbitals? Do electrons in the 's' orbitals move in a relatively 'circular' sort of motion or is it completely random within the orbital?
    What about the 'p' orbital? I do know that it has two "sections"(the two balloons) Does each section contain an electron each? and how does it move wthin the 'p' orbital?
    Just to be clear. I initially believed that electrons moved around nuclei just as planets move around the sun (rotation that is). But what is the concept of orbitals then?

    I know these are a lot of questions :confused: but any help or references are appreciated.
     
  2. arauca Banned Banned

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    My explanation is in parables : Think about the satellites the earthlings have placed above the earth some go around the equator some go around the pols they are placed in some particular orbits, and if you look in coordination ( x,Y,Z ) so there are many ways around and so are the orbits. Now if you think that the earth exerts gravitational pool . The gravitational force is related to the distance from the big mass and so the strongest attraction nearest to the mass so is the s orbital and by Pxyz then d orbital and so on .
    I am sure some other intellectual over here will explain you in a more scientific language .
     
  3. AlexG Like nailing Jello to a tree Valued Senior Member

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    The electrons don't 'move' in the orbitals. They have a probability of being somewhere within the obital.

    I usually don't like referencing something like yahoo.answers, but in this case it's a good answer.

    http://in.answers.yahoo.com/question/index?qid=20070118034625AAqsxrF
     
  4. exchemist Valued Senior Member

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    1,700
    In Quantum Mechanics, which is needed to explain how matter at the atomic scale behaves, the concept of a "particle" becomes problematic. Instead, one deals with "wave-particles", which behave in some respects like a particle and in others like a wave. The concept of the "orbital" was developed to replace the old Rutherford-Bohr idea of the "orbit" of an electron, moving round the nucleus like a planet around the sun, with something that recognised the wave-like aspect. The orbital is like a "probability wave", the probability being the likelihood of finding the electron at various points in space. The electron in an orbital has kinetic and potential energy, so is a bit like an orbiting planet. It also has a "spin", a bit (though not wholly) like a planet spinning on its axis. However, unlike an orbiting planet it may or may not have any angular momentum! Electrons in s orbitals have no angular momentum, while those in p, d, f etc orbitals do.

    It is impossible to track a trajectory for an electron in any of these orbitals: all one can say is there is a probability of finding them at a certain point, given by the mod square of the amplitude of the "wavefunction" (a.k.a. state function or eigenfunction) at that point. One knows less about the motion of a "particle" in QM than one would in classical mechanics. This is most famously encapsulated in Heisenberg's Uncertainty Principle, which sets limits on what information one can have simultaneously about a QM wave-particle.

    The various types of orbital can be compared with a standing wave, e.g. in the fundamental and harmonics of a resonating vibrating string. The 1s orbital has only +ve phase (fundamental) while the 2 s (1st "radial" harmonic) has 2 concentric spherical shells, one of +ve phase and one of -ve phase. The 2p has one lobe of +ve phase and one of -ve phase, so this too is an "harmonic" but angular rather than radial this time, so "vibrating" differently in space. (Incidentally a vibrating rubber ball will have rather similar resonant modes of vibration.) Each orbital can contain 2 electrons, with opposed spin orientations (the Pauli Exclusion Principle limits it to 2). Each electron occupies the full orbital however.

    Some of this is very counterintuitive, which is why I found (and still find) it so fascinating. If any of this is unclear I'll do my best to try to find alternative ways to describe it to make it clearer.
     
  5. arauca Banned Banned

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    You better stop reading and reviewing , because it makes you seam sophisticate but it does not say about to make an individual wants to understand . Come back as a chemist .. ha ha
     
  6. Brett Registered Member

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    Nothing is random, as everything is determined. if you were to observe the moving electrons, you will notice that something else needs to be moving too, or, exerting force upon the electron.

    To determine where the electron will go next, you need to observe where the electron has been previously. of course electrons repel each other, so maybe the s and p orbitals affect one another?
     
  7. Muzaffar Registered Member

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    thank you exchemist for such a detailed yet coherent explaination. I seem to be getting it except one thing. And that is the "behaviour of particles as waves". What exactly does that mean?
     
  8. Brett Registered Member

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    What does a wave do but push and transmit things?
     
  9. Layman Totally Internally Reflected Registered Senior Member

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    I would think that they move in orbitals and there is a probability of them being somewhere in the orbital. The entire reason there is just a probability of it being somewhere is because you cannot know the exact speed and position at the same time due to the uncertainty principle. This does not mean that the electron does not move around the nucleus, it just means you don't know exactly where it is while it is moving around the nucleus. Opposites attract, if it was just sitting there it would fall into the nucleus, observation of the speed of an electron in an atom wouldn't create an ion.
     
  10. AlexG Like nailing Jello to a tree Valued Senior Member

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    The only rejoinder I'll make to this is that you know nothing about quantum mechanics. It wasn't in that tech manual.
     
  11. Layman Totally Internally Reflected Registered Senior Member

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    I will take this that you misunderstood what was meant for there to be an electron cloud and you are a jerk.

    You cannot know the exact speed or position of a particle, therefore you cannot say that it is completely motionless, period.
     
  12. Muzaffar Registered Member

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    Fine. But what about the movement of electrons in a rotation around the nucleus as suggested by Rutherford? Has it been declared invalid now that the concept of orbitals has been introduced?
     
  13. exchemist Valued Senior Member

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    Yes! It has been entirely superseded by the concept of standing wave - like "orbitals", instead of classical mechanical orbits. Sometimes you will find the "classical picture used for the purposes of simple analogy, but always with the proviso that this is not how it really is.
     
  14. exchemist Valued Senior Member

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    That is a question that is still argued over, among those interested in the philosophy of Quantum Theory. You get this with light of course. We can see light reflected, refracted and diffracted, and we know it has a wavelength and frequency, all of which are wave properties. But it seems it can only be emitted or absorbed in discrete units (which we call photons) and it can exert pressure on a surface on which it falls, which is particle-like behaviour. With beams of electrons and other particles of matter, we find we can also get diffraction effects (interference fringes for example). Which is wavelike behaviour! The wavelength of a particle is related to its momentum, by de Broglie's relation: lambda = h/p, in which lambda = wavelength, p = momentum and h is Planck's constant. So higher momentum particles have a shorter wavelength - or higher frequency.

    As to what the "waves" are, that's a good question. The things that make a thing seem to exist are the properties of it that one can measure. With Quantum Mechanics one needs a short excursion into the maths and then back again to see how physical properties relate to the waves. In QM, all the information about a wave-particle in a particular state is contained in something called its "state function" or eigenfunction, or sometimes wavefunction. This complex-form mathematical function has wave-like qualities. (If you ever study alternating current theory in physics, you will find complex numbers crop up there as well - because that is also a theory of waves.) To determine the value of a physical property, such as energy or momentum, one "operates" mathematically on the state function with the appropriate QM operator. The simplest operation is for position. To find the probability of the particle being found in a given volume of space, one multiplies the function by its complex conjugate (this is the complex number equivalent of squaring it) and integrates this over the volume of space in question.

    So, you can think of the "waves" as being waves of probability, or rather, the square root of probability. The pictures you see in textbooks of the shapes of orbitals are plots of the probability obtained in this way. But you cannot hope to know everything about a particle at once, in the way you can in classical physics. Heisenberg's Uncertainty Principle says that delta p.delta x >/=h/4 pi, in which delta p and delta x are the uncertainty about the momentum and position of the particle and h is again Planck's Constant. This is why you cannot track the "orbit" of an electron. If you could write down an orbit for it, you would be able to say what its position and momentum were exactly. In QM, this CANNOT be done. And the reason why is the inherently fuzzy nature of the probability waves which determine what you are allowed to know about a system of particles.

    It is not easy and has troubled the best minds of science. Einstein himself hated it, saying God does not play dice. But, all the evidence is that God DOES play dice and that probability waves are how matter really does behave on the atomic scale.

    My best advice to you, since you are starting out on this mysterious adventure, is to pay close attention to anything you are taught in physics concerning waves: wavelength and frequency, phase, amplitude and energy, reflection, refraction, diffraction, resonance and standing waves, constructive and destructive interference and what happens when you superimpose waves of different frequencies on top of one another. All these come up time after time in QM and are used to explain all sort of things in chemistry, from atomic and molecular spectra to chemical bonding itself. So if you understand waves, you will "get" QM - at least qualitatively.
     
    Last edited: Jul 2, 2013
  15. Trippy ALEA IACTA EST Staff Member

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    Sorry, I didn't see this thread earlier.

    There's not much I can add to Exchemists responses, he's done a fantastic job of explaining it here.

    The only thing I can really add is that there's been a similar discussion here in this thread: Some Basic Doubts In Chemistry including some of the differences between new quatum theory and old quantum theory, and how they relate to Orbital shapes.
     
  16. exchemist Valued Senior Member

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    Er, right. So you think I "seam sophisticate but it does not say about to make an individual wants to understand"? Ah. I should perhaps leave it to such models of crystal clarity as yourself, you mean?

    On the other hand, the poster of the OP seems to have got most of it and come back for more, which suggests it can't have been too incomprehensible. Perhaps it is you who needs to "come back as a chemist"!:)
     
  17. arauca Banned Banned

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    Well I did not mean in an offensive way, I had some instructors mention about QM in the early 1964 it was very impressive about di atomic molecule and I am not sure in the last 50 years it have advanced much more , but chemical product and synthesis and analysis have advances much more. The problem is we want to look intellectual, so we recourse to the so called theoretical area were a lot of paper and fancy math is used, then we can be part of an intellectual discussion but coming to chemistry we use the same ancient principle were QM is not involved . Can you tell me how the wave function will help you to polymerize some monomers , plate out some metals ,or even some closer : corona discharge to modify surface of a polymer and so on. Of course in school those classes have to be taken and to have some understanding, otherwise you don't graduate because is part of the curriculum.
    I don't mean any offense it is only a discussion, you know what I mean .
     
  18. exchemist Valued Senior Member

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    OK arauca no hard feelings, I know what you mean. But if you tease me, you must expect that I tease you!

    Seriously though, both types of chemistry have value. It's impossible to understand things such as the spectra of molecules without QM and there are huge classes of phenomena in physical chemistry that depend on it. Even the "octet rule", used in basic short period chemistry, can't be explained without the Aufbau Principle. But it depends which parts of the subject take your fancy. For me, as a philosophically inclined guy, the best part of the subject was the counterintuitive phenomena and the weirdness of the quantum world. So I focused on physical chemistry and quantum chemistry in particular. For others with a more practical inclination, a lot of synthetic chemistry can be done without wondering too much about it. But if you ever start delving deeply into WHY reactions go the way they do, you come up against QM principles pretty rapidly.
     
  19. Trippy ALEA IACTA EST Staff Member

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    It has advanced, substantially. We now have Frontier Molecular Orbital Theory which correctly predicts some of the oddities in chemistry (things like why rule violations occur).
     
  20. arauca Banned Banned

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    Great , but you have to depend on functional groups attached to a given molecule if you want to do some reaction or if you have a catalyst as an example you have Atactic , sindiotactic and Isotactic polypropylene or other
     

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