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## Main Question or Discussion Point

**orbit n orbital!!**

hi, what is the difference between Orbit and Orbital??? when electron is moving so fast, how can we assume of arranging them in an arbital? I am unable to get the actual concept!

- Thread starter photon79
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hi, what is the difference between Orbit and Orbital??? when electron is moving so fast, how can we assume of arranging them in an arbital? I am unable to get the actual concept!

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An arbital is a spatial volume whithin which you can find a particle (eg an electron) with a certain probability.

ELECTRONIC ORBITAL

marlon

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According to PF guidelines, you are not allowed to double post. Just so you would know.

marlon

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good question. Molecular orbitals are different from atomic orbitals, though molecular orbital theory states that for every atomic orbital, you get exactly one matching molecular orbital.

When 2 atoms make a molecule, they of course share the electrons. The s, p, d, f, g etc. atomic orbitals that you're used to fuse and make sigma, pi, delta, etc. molecular orbitals. These have very specific shapes and are very useful in predicting where things are in molecules and even in solids (the field in which I work). It get's a little wackier b/z you have to keep in mind that these things have 1) energy levels 2) are quantum mechanical in nature so eigenfunctions, etc. apply 3) the molecular orbitals (MO or MO theory) have phase and this directly impacts the results.

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Could someone tell me how and why do the electrons move in orbitals? And how do the forces balance each other? Why are there energy differences in orbitals of the same orbit, whereas it is said that orbits have quantised energy?

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Orbit and orbital are exactly what marlon described. As for electrons' motion, they move in a circular motion in the orbitals, due to their angular momentum and forces acting on them. The orbitals came into light to explain the spectrum lines and the Zeeman and Stark effect. That can't be expalined by Bohr's model. Hope you get my point. One thing I didn't get was the fact that their are energy differences in orbitals of the same orbits. How is that possible if orbits are assumed to have quantised energies?photon79 said:hi, what is the difference between Orbit and Orbital??? when electron is moving so fast, how can we assume of arranging them in an arbital? I am unable to get the actual concept!

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you cannot ask about the motion of electrons in orbitals because orbitals are a spatial region where you have a certain probability of finding an electron. This is a manifestation of the Heisenberg uncertainty principle. If you would say that the electron motion is on an orbit in an orbitals, than why would you need the actual orbital for ? I mean, saying the motion is on an orbit implies that you know the exact electron's path. This is completely contradictory and veeeery wrong. forget about ...Neha Sanghvi said:Orbit and orbital are exactly what marlon described. As for electrons' motion, they move in a circular motion in the orbitals, due to their angular momentum and forces acting on them. The orbitals came into light to explain the spectrum lines and the Zeeman and Stark effect. That can't be expalined by Bohr's model. Hope you get my point. One thing I didn't get was the fact that their are energy differences in orbitals of the same orbits. How is that possible if orbits are assumed to have quantised energies?

marlon

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regards

marlon

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SpaceTiger

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Come on, marlon, you know it doesn't have to be a circle.marlon said:Orbit is a circular path (in space)

To expand on (or, perhaps, reiterate) what marlon has already said, the term orbit is usually used to describe the paths of celestial bodies (like planets and asteroids) around more massive ones (like the sun), but it has been extended to other things. For example, the Bohr model asserts (incorrectly), that the "orbitals" of an atom are analogous to the orbits of planets around the sun. That model was proposed before the development of quantum mechanics, so it was later superseded, but I suspect that it was the historical reason for referring to the bound wave functions of the atoms as "orbitals".

Some ways in which the concepts are the same:

- In both cases, a less massive body is bound to a more massive one.

- In both cases, you can associate an "energy" with the orbit or orbital.

- In both cases, the orbits or orbitals can take on various configurations with the same energy (distinguished by, for example, angular momentum or the angular momentum quantum number)

Some ways in which the concepts are different:

- Quantum orbitals can only take on a discrete set of energies, while orbits can occupy any energy in a continuous range.

- Objects in orbit are said to have a well-defined position and momentum at any given time, while orbitals represent a probability distribution for finding the object in a region of space.

- Orbits can be studied without being disturbed, while a measurement on an orbital will "collapse" the wave function and change the state of the system.

There are plenty more, but I suggest reading a textbook on quantum mechanics for the full story.

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Right, I got ur point. But, I dont get one thing. Why are there energy differences amongst the orbitals? I mean if the energy levels are quantised, then there shouldnt be any differences. And if they are not, that would mean that the quantised energy is actually very small in magnitude, appearing to be almost continous. So, is this correct?marlon said:you cannot ask about the motion of electrons in orbitals because orbitals are a spatial region where you have a certain probability of finding an electron. This is a manifestation of the Heisenberg uncertainty principle. If you would say that the electron motion is on an orbit in an orbitals, than why would you need the actual orbital for ? I mean, saying the motion is on an orbit implies that you know the exact electron's path. This is completely contradictory and veeeery wrong. forget about ...

marlon

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Could anyone please clarify this concept?

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I think the excitation of an electron in an orbital with insufficient energy is a radiationless process in which the excess energy is dissipated as heat. Photon will excite the electron ,but as the electron can not reach higher energy level it will return to its ground state without emitting any radiation involving some heat dissipation.Neha Sanghvi said:

Could anyone please clarify this concept?

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Claude Bile

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It is not absorbed and reemitted, this is a wholly different type of interaction.

Also Photon79, how do you propose an electron dissipate heat as a radiationless process?

Claude.

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Claude Bile

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If the energy of the photon matches an energy gap (or is close to an energy gap), there is a significant chance that the electron will absorb the energy of the photon and change its orbital correspondingly. The closer the energy is to the energy gap, the likelihood of the photon being absorbed increases.

Claude.

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I got the point that if the energy of the photon matches an energy gap, the electron will change its orbital accordingly. But why would it change if the energy of the photon is close to an energy gap? I mean that would relate to my former question of insufficient energy. And I didn't get your idea of the absorption of insufficient energy by an electron. Could you please explain it again?Claude Bile said:

If the energy of the photon matches an energy gap (or is close to an energy gap), there is a significant chance that the electron will absorb the energy of the photon and change its orbital correspondingly. The closer the energy is to the energy gap, the likelihood of the photon being absorbed increases.

Claude.

Thanks.

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Claude, isn't your idea of insufficient energy absorption the same as that of photon79's?

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Claude Bile

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Also, keep in mind that there is an inherent probability as to whether the photon is absorbed. Even on strong resonances, there are some photons that will not be absorbed. By the same token, there are some photons that do not lie near any resonances, yet are still absorbed.

If the photon is not absorbed by the electron, the photon will transmit through the electron unperturbed (with the exception of a slight phase shift).

No. Either the photon is absorbed and the electron is promoted or there is no interaction at all. Photon also seems to think that atoms can just somehow remove their heat without radiating it away, a notion I dispute.Neha Sanghvi said:Claude, isn't your idea of insufficient energy absorption the same as that of photon79's?

P.S. This is not 'my idea' this is the established view of photon/atom interactions, as much as I would like to take credit for it .

Claude.

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Why is this so? I mean, what did you mean by inherent probability? Could you please explain that?Claude Bile said:Also, keep in mind that there is an inherent probability as to whether the photon is absorbed. Even on strong resonances, there are some photons that will not be absorbed. By the same token, there are some photons that do not lie near any resonances, yet are still absorbed.

Claude.

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Claude Bile

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Claude.

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Orbitals take on very specific shapes, but it's within those shapes that you have the "hazy" electron density you described. You can look them up: s, p, d, f, g, etc.

The shapes themselves are really beautiful. They are actually a special class of polynomials called "Legendre Polynomials". Legendre polynomials can be seen in other "energy-related" systems. For example, energy minima on our sun conform to these patterns.

Your suspicion that electrons w/ insufficient energy to truly ionize "jump" to higher excited states (and, therefore, orbitals) is correct. The theory is more complex than that, but you get the right idea. Before ionization, there are hundreds of higher excited states. As a matter of fact, the number of states at a given energy level is called "density of states".

Even hydrogen has d orbitals. Of course, they're empty unless an electron were excited to that state.

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