Infamous_Reddy
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Why don't electrons lose energy when revolving?
When the electrons revolve around the nucleus, they do so in shells which leads to no loss or gain in the energy of the electron. Why is this? I mean
something moving should require energy, right?
Thanks
[Edited on 5-7-2021 by Infamous_Reddy]
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Antigua
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Your presumption is wrong. Throw a ball into space and... it'll never stop going forward unless something stops it. Movement itself isn't "work" and
energy cannot be lost by it. (This is in simple terms, as with all matters of microphysics it's more complicated than that).
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Infamous_Reddy
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Quote: Originally posted by Antigua  | | Movement itself isn't "work" and energy cannot be lost by it. (This is in simple terms, as with all matters of microphysics it's more complicated than
that). |
I agree, I also thought the same at the beginning. As the electron revolves in circular/elliptical orbits, it undergoes no displacement as at some
point, its final position is equal to its initial position. It undergoes no work but, energy is still consumed. Suppose a man moves a block along a
circular path and stops exactly at the point he started at. In this scenario, the work done is zero but energy is still consumed.
Why did the Rutherford's model of the atom fail and the Bohr's model succeed (well, at least in this aspect)? It is taught to me that the Rutherford's
model of the atom didn't take into account that the electron will gradually lose energy and get attracted to the nucleus as unlike charges attract
each other which, doesn't explain the stability of the atom. But, the Bohr's model somehow deals with this problem by the concept of specific energy
orbits (shells).
PS: Sorry for posting this in the wrong type of forum (I meant to put it in "Beginnings").
[Edited on 5-7-2021 by Infamous_Reddy]
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SWIM
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Not so much orbits as standing waves.
I know they still call them 'orbitals' but there's more to it than that.
If the electrons were just whizzing around like planets there wouldn't be a limited number of discrete orbitals and hybrid orbitals.
This is getting into quantum mechanics, and There are many posters on this board far more qualified to explain it than I.
So I'm not going to risk muddying the waters with some half-assed explanation when I am confident a well reasoned and succinct post by somebody who
really knows this stuff or even actually teaches this stuff will likely be turning up soon.
Is Blogfast25 still around? He'd probably love answering this.
EDIT: I got curious and checked. No, he's not still around here.
Hope he's doing well even though he had to give up chemistry.
[Edited on 5-7-2021 by SWIM]
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Texium
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Thread Moved
5-7-2021 at 10:49 |
Fulmen
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You're kinda on the right track but for the wrong reason. Yes, in Rutherford's model energy would be lost, but only due to it's electric charge. In
gravity all losses are secondary effects, no net energy would be lost, gained or consumed from a point mass in absolute vacuum.
But electrons have a charge, and that would cause it to emit electromagnetic waves. If an electric charge is placed in an electric field, the charge
will be accelerated. That means that a charge subjected to acceleration (any circular motion involves acc) must generate an electric field.
So the orbit model can't be right as an atom would decay in a fraction of a second.
The solution is to apply quantum mechanics. Electrons are not physical objects like marbles, in fact any macroscopic analogy will be inherently
flawed when applied to the quantum realm.
Subatomic "particles" are no longer solid objects with an exact position in space and time. We can only describe them through probability functions.
We're not banging rocks together here. We know how to put a man back together.
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j_sum1
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You have a number of misconceptions here, I_R.
First, and most critical is that you seem to be visualising electrons as little dots that travel in circles. That is simply not an adequate model for
describing the movement of electrons in an atom. At this scale, wave-particle duality is significant. And a wave model is much better suited to
explaining electron behaviour.
However, this does not resolve your question. Your second misconception relates to a misunderstanding of what work is in the physics sense.
Work may be simply defined as force × distance.
However, like most introductory definitions, this is something of a simplification. It is contingent on the notion that the distance moved is in the
same direction as the force being applied.
More properly, work is the scalar product of force and distance. (See Wikipedia.)
Practically, this can be calculated as force × distance × cosθ where θ is the angle between the two vector quantities.
In the case of an orbiting body such as a planet moving in a perfectly circular orbit, the direction of movement is tangential to the orbit circle.
The force is provided by gravity and is directed towards the star being orbited. Thus it is at right angles to the direction of movement. The cosine
of a right angle is zero and therefore no work is being done.
Two minor complications arise.
1. Orbits are seldom perfectly circular. This means the angle is not always 90°. This means that some work may be being done. The planet will
alternately speed up and slow down.
At the same time it will move closer to and further away from the star it is orbiting. It would be acurate to view this as a transfer of energy
between gravitational potential and kinetic energies. The total energy in the system remains the same so the law of conservation of energy is not
broken.
2. In reality, energy is lost from a planetary system over time. Space is not a perfect vacuum. And the presence of other orbiting bodies means
there is continual energy transfer between planets. Thre is no analogous behaviour with electrons. There is no friction at the quantum level.
Gravitational systems are easy to visualise. However the same principles apply for systems set up in other fields: magnetic or electrostatic.
Electrons in an orbital will not violate the law of conservation of energy. If you wanted to, you could visualise them as orbiting particles and then
calculate such quantities as orbital radius, orbital velocity, angular momentum etc. The mathematics would work and you would have a consistent
model. It just would not be a good reflection of the actual behaviour of electrons.
Here is my video on electrons which is something of a primer for electron orbitals.
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j_sum1
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| Quote: Originally posted by SWIM | Is Blogfast25 still around? He'd probably love answering this.
EDIT: I got curious and checked. No, he's not still around here.
Hope he's doing well even though he had to give up chemistry. |
It was a condition of his release that he not engage in home chemistry or in internet groups on the topic. I am not sure of the time frame imposed.
My guess is that he was sufficiently burned to throw the whole thing in. His personal blog ceased as well. I really feel for him.
He has lurked on occasions but I seriously doubt he will post again. Certainly not under the same name.
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woelen
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Macroscopically, orbiting objects lose energy. Orbiting charges lose energy through electromagnetic waves. Orbiting masses lose energy through
gravitational waves (recently these were really discovered, originating from two black holes, which were orbiting each other and due to loss of energy
fell into each other in an inward spiralling orbit). Earth also loses gravitational energy, while moving around the sun. This loss of energy is low,
just a few tens of watts. Much more energy is lost, due to tidal effects (friction inside the earth) and friction with solar wind, but even if these
effects were not present at all, the sun-earth system would lose energy, very slowly, due to emission of gravitational waves.
In the quantum-world, these macroscopic concepts, however, cannot be used anymore. Others already mantioned orbitals, and an orbital is something
different than an orbit. Electrons, being in an orbital, have a certain energy level and that energy level is fixed (actually, it is fixed very
precisely).When an electron moves to another orbital, it either needs to consume a certain amount of energy (which can be supplied by a photon), or it
releases a certain amount of energy, which can be observed as a photon (we observe these as light). This is what causes the nice glow in fireworks
with all kinds of colors.
The electromagnetic properties of orbitals at the quantum level are well understood. At the gravitational level we know next to nothing. Electrons
have both charge and mass and none of these cause emission of energy in orbitals. Gravity at quantumlevel is still not understood and there is not a
single well established theory, which covers this.
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Infamous_Reddy
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Thank you for making me understand this concept better Fulmen, j_sum and Woelen. That sum_lab video was especially helpful.
Also, can anyone share any textbooks or relevant literature that explains the atomic structure from the basics? I am just starting out with the theory
of Physical Chemistry and want some help getting started.
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zed
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Blogfast? Well, he blogged fast... and often with a lack of politeness.
I just read up on his dilemma. Seems he trusted someone, that did something terrible.
That habit of trusting people; I can't abide it. They will disappoint you, all too often.
Perhaps he lacked wisdom, but other than that, I see little evidence of any real crimes.
In my jurisdiction, having some Nitric Acid, and some peroxide, and a few other odds and ends, probably wouldn't be considered a crime. Certainly not
so, if you lacked intent to commit some dastardly act.
Most explosive materials and poisons, simply aren't inherently illegal to possess.
Why should they be? Hereabouts, decent people solve their disputes with handguns.
As for electron-spin and what-not. The more I learn; the less I understand.
Higgs Bosons, Dark Energy, Dark Matter, WIMPs, Anti-matter... UFOs.... Anti-gravity?
And... Why is there still a Universe?
Well, no-one is quite sure.
Lotsa good lectures on YouTube, if you have a good connection.
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chornedsnorkack
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| Quote: Originally posted by Infamous_Reddy | | When the electrons revolve around the nucleus, they do so in shells which leads to no loss or gain in the energy of the electron. Why is this? I mean
something moving should require energy, right? |
That´s actually Aristoteles´ idea.
The common observation is that macroscopic objects on ground moving slow down and stop unless something continues pushing them.
What Galileo and Newton pointed out is that macroscopic objects on ground slow down due to friction against something else - if there is little
friction, like in case of good vacuum, they keep moving.
Still, another matter is that charges in accelerated motion, including uniform but curved motion, experience friction by radiation in macroscopic
scale, which is the problem with Rutherford atom.
What Bohr discovered is that orbits are actually quantized. An electron in a circular orbit in the magnetic field of a synchrotron radiates. Because
the electron in a synchrotron has a huge quantum number and many lower states, many of which are unoccupied. A highly excited atom also has a huge
quantum number and many options to radiate. But a ground state cannot radiate, because there are no lower states or they are all full.
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zed
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Ah! A little more about electrons and what not.
This should render things crystal clear! (heh,heh,heh)
https://www.youtube.com/watch?v=O4Ko7NW2yQo
Particles are so fickle. You can't even get electrons to seriously commit to being electrons.
Hmmm. Perhaps I should watch this thing a few times more.
[Edited on 8-7-2021 by zed]
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macckone
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The reason electrons don't lose energy is basically quantum mechanics.
They can only exist in standing waves that result in the electron being in a single 'orbital state'.
To change energy they must move to a lower 'orbital state'.
But only one electron can exist in each 'orbital state' and there is a minimum possible 'orbital state'.
So if all electron lower energy 'orbitals' are filled and there are no empty lower energy 'orbitals',
the electron cannot lose energy.
It is simply impossible under the laws of quantum mechanics.
Quantum mechanics was a solution to the problem of electrons not losing energy.
Each orbital corresponds to a 'spin' and a complete wave.
Spin allows two shells to exist at the same wave position.
ps. this is a very simplified explanation of quantum mechanics in relation to atoms. It is not 100% accurate or anywhere near complete. entire books
have been written on this.
[Edited on 9-7-2021 by macckone]
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Hoffit
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Way back it took me a while to get my head to figure out where the electrons are if they do not orbit. The reason they don't radiate em waves is
because the don't orbit the nucleus like planets. Electrons just exist in the orbital. Not in a single point that moves within the orbital but
everywhere in the orbital, at all allowed locations at the same time. Some locations in the orbitals are of more probable than some others.
Only if you measure it, you find it at some definite location and not somewhere else. Quantum mechanics is so weird. Electron can be on top of the
nucleus at the same time it is below it and so on.
Waves are another way to visualize it. It is often easier to understand wave can be at multiple locations. Everyday objects are not at multiple
locations at the same time after all.
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