electron speeds

[someguy]

I was just wondering, what sort of speeds do electrons move around at while they are in probability clouds?

[Klaynos]

They don't move. They are not at a single location in the probability cloud, but they are distributed across it, in this case we must consider them as waves.

 

If they where moving they would be accelerating (as they would be moving in a circle or other curved movement) which means they would be radiating energy all the time, which obviously can't be happening.

[someguy]

light has a speed and it is a wave/photon so if you want to look at an electron as wave/electron then this property itself cannot be a factor preventing speed calculation. Heisenberg states that you can either know their speed or their location so barring technical difficulties knowing their speed by sacrificing knowledge of their position should be possible I think. If their location changes they must be moving mustn't they?

[Klaynos]

light has a speed and it is a wave/photon so if you want to look at an electron as wave/electron then this property itself cannot be a factor preventing speed calculation. Heisenberg states that you can either know their speed or their location so barring technical difficulties knowing their speed by sacrificing knowledge of their position should be possible I think. If their location changes they must be moving mustn't they?

 

Photons are not normally stationary waves though. If we put a photon inside a 100% mirrored box I don't think c is meaningful as it's speed any more because it's not propagating, in the say way in an orbital an electron is not propagating.

[someguy]

what do you mean? if they are not propagating what are they doing? why would a reflective box cause a wave to change like this?

[Klaynos]

There is a difference between being a moving particle with a set speed and being a probability wave confined to a region with an undefined speed.

 

Electrons in orbitals CAN NOT have a speed because as the velocity would have to be constantly changing they would be an accelerating charge.

 

Accelerating charges radiate, so they would be losing energy all the time, where would this energy come from?

[someguy]

I f they accelerate and decelerate they can share energy with each other. I understand how the question is not so easily answered as the speed of a car. but if an electron is not moving, and yet moving, it sounds like they must be magic or something. i am not really sure why you say they must accelerate and therefore require energy from somewhere. a sattelite in conventional orbit accelerates and never requires additional energy. if they are not moving, and acceleration is a change in speed how can they be accelerating? how can they change from one speed to another and yet not ever be at any speed at all?

[grifter]

We tend to think of electrons in atoms like planets

orbiting the sun. While this view can often be useful, the first theories of atom structure by Bohr, is a gross simplification. The electron should be considered as smeared out over a large volume surrounding the atom. In this sense, the electron does not move inside the atom, as Klaynos has pointed out

 

But still it is possible to ascribe approximate velocities to electrons in bound states. This is done to ascribe whether relativistic effects are important in calculating said bound states e.g. relative contraction of the inner core of electrons is normally used to explain some of the properties of transition metals, and relativistic corrections to calculations, are currently a pioneering physics. A gross model for "speeds" of electrons in bound states can be obtained from the Bohr model. This model predicts the electron (associated with a hydrogen nucleus) is moving at 2.42 x 10⁸ cm sec^-1 (ground state) this is pretty small compared to the speed of light...

 

BUT I MUST STRESS (notice I'm stressing, because I'm using capitals )

AS I SAID ABOVE KLAYNOS IS CORRECT, THE ELECTRONS ARE NOT MOVING....

[someguy]

ya, i know what you mean about the bohr model being old school, i didn't mean to imply that electrons orbit conventionally i meant only to demonstrate that objects can accelerate continuously without conflicting with the theory of conservation of energy. thx for the values! I've been trying to figure this out for the longest time. I was just wondering one other thing, do you know how they arrived at these values?

[grifter]

Yes the Bohr model is old, but thats the only way I could think of to find a value for velocity... but as Klaynos and I have stated......the electrons have no velocity, this dated model is you r best bet, I forund the value like so :

 

[math]

\frac{Kq_e^2}{r} = m_e v^2

[/math]

 

to find v use this:::

 

[math]\frac{k q_e^2}{n \hbar} = v[/math]

 

 

where:

 

[math]\hbar = \frac{h}{2\pi}[/math]

 

[math]n =[/math]1,2,3,4 (quantum number)

 

[math]q_e = [/math] charge on electron

 

[math]k = \frac{1}{4 \pi \mathcal{E}_0}[/math]

 

now for a bit of math

 

[math]

\frac{2.55 \times 10^{-42} \times -1^2}{1 \times 1.05\times10^{-34}}

[/math]

 

[math]\frac{2.55 \times10^{-42}}{1.05\times10^{-34}}[/math]

 

and yes:

 

[math]\frac{2.55 \times10^{-42}}{1.05\times10^{-34}} = 2.42\times10^{8} [/math]

 

okay?

[Klaynos]

objects can accelerate continuously without conflicting with the theory of conservation of energy.

 

No they can't if they are charged, a deceleration is just a negative acceleration so the electrons would still give out energy. A curved motion is a continuous acceleration.

[someguy]

ooh i didn't realize you meant that you would use the bohr model in order to approximate a speed for the sake of argument, sorry, i thought you were commenting on my previous post about sattelites thinking i thought the bohr model was actually the way it is. I thought you just found that number somewhere from an experiment someone else did, i didn't realize you derived it that way. That was a pretty good idea. Apparently the bohr model is pretty good for calculating the energies of electrons for a hydrogen nucleus even in multiple orbits. I don't completely understand why your formulas are that way, I wish i did, but they were still very helpful. Thanks grifter.

 

Klaynos

 

If an object has a certain value of kinetic energy and is negatively accelerated this value would diminish and this energy would need to go somewhere this i see would give out energy but for something accelerating the opposite would occur the object's kinetic energy would increase and so the object would have absorbed energy. this is why i said that electrons could be sharing energy with each other slowing down and speeding up. How come not if they are charged?

[Klaynos]

If an object has a certain value of kinetic energy and is negatively accelerated this value would diminish and this energy would need to go somewhere this i see would give out energy but for something accelerating the opposite would occur the object's kinetic energy would increase and so the object would have absorbed energy. this is why i said that electrons could be sharing energy with each other slowing down and speeding up. How come not if they are charged?

 

I am not talking about kinetic energy.

 

Charged particles that are accelerating radiate energy, they send it out as photons. This normally comes from whatever is trying to accelerate them, but in the case of electrons around atoms with no outside force there is nowhere for this energy to come from.