# Orbit n orbital

## 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!

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Orbit is a circular path (in space)

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

ELECTRONIC ORBITAL

marlon

ok thankyou malron,,,but what about molecular orbitals? the different shapes given for them are because of sharing of electrons where as the concept of finding a partical remains the same as in atomic arbital..i think i am correct,,.

Photon79, just a policy remark.

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

marlon

Photon79 -

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.

Movement of electrons in orbitals

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?

I think this is it, though I am not quite sure myself

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!
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?

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?
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

The zeeman and Starck effect are not the reason why we invented orbitals... again, first make sure you know what an orbital is. I would also like to ask you what the Zeeman and Starck effect is ? If you study these phenomena, you will see they have something to do with electronic-energylevels splitting up if you place an atom in an extern magnetic/electric field...The fact that you speak about electronic energylevels already implies you are using orbitals because orbitals are used to caracterize the energy of an atom/electron/...

regards
marlon

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

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.

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
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?

Another thing I wanted to ask was that if an electron gets enough energy to be free ( ionisation energy ), then it leaves the atom, but if it does not get enough energy to jump from one quantised level to another, it remains in the same orbital. So, how can a electron, with more energy than it is supposed to have in that particular orbital, stays in the same orbital?
Could anyone please clarify this concept?

And by circular motion, i didnt mean proper one. They move around in a hazy cloud sort of way but in a circular manner. I read this point in more than 5 books, but i still haven't understood the mechanics behind it. so, if anyone can, please do it. i will be grateful.

An electron on a particular orbital will have the energy the oribital corresponds to. If you try to excite it with insuffcient energy it'll remain on the same orbital. I'm not sure but I think that the photon you used to try to excite the state will get absorbed and re-emitted (with the same energy it originally had). As for the energy differences of course there are energy differences between the orbitals when there are bound states. Why do you think quantization of energy would imply otherwise?

electron in orbital

Neha Sanghvi said:
Another thing I wanted to ask was that if an electron gets enough energy to be free ( ionisation energy ), then it leaves the atom, but if it does not get enough energy to jump from one quantised level to another, it remains in the same orbital. So, how can a electron, with more energy than it is supposed to have in that particular orbital, stays in the same orbital?
Could anyone please clarify this concept?
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.

Claude Bile
There is an overwhelming probability that a photon incident on an electron will pass through the electron if the energy of the photon is not resonant (i.e. does not match with an electronic energy gap).

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.

Yeah thinking about it now a/r-e process wouldn't make any sense since in this case the transition rules wouldn't be satisfied.

then, claude, what is the fate of the electron which has got insuffiecient exciting energy, i strongly believe here the electron will vibrate n dissipate energy to its surroundings. neither it is excited completely nor it can sit as such after recieving that energy!!

Claude Bile
A photon incident on the electron will cause the electron to oscillate. IF the energy of the photon does not match an allowed transition, the electron will (overwhelmingly probably) return back to its original state after oscillating and the photon will continue on its merry way.

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.

Claude Bile said:
A photon incident on the electron will cause the electron to oscillate. IF the energy of the photon does not match an allowed transition, the electron will (overwhelmingly probably) return back to its original state after oscillating and the photon will continue on its merry way.

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.
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?

Thanks.

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

Claude Bile
Energy levels are not discrete, they have a finite linewidth. This finite linewidth is due to the Uncertainty Principle. The more stable an energy level is, the smaller its linewidth. Because such linewidths are Lorentzian (wrt energy), they don't technically ever reach zero. Hence it is not IF you land on a resonance, but how close you land to a resonance peak so to speak, that is important.

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).

Neha Sanghvi said:
Claude, isn't your idea of insufficient energy absorption the same as that of photon79's?
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.

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.

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.
Why is this so? I mean, what did you mean by inherent probability? Could you please explain that?

Claude Bile
When you solve Schrodinger's equation you get a probability of the atom finishing in one state or the other.

Claude.

Hi, all -

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.