Atoms questions!!

[hitmankratos]

Hello everyone,

 

Today in class, we learned about the Rutherford experiment.

Ernest Rutherford is the one discovered the nucleus of the atom with his experiment. What he did was that he "fired" alpha particles coming from a radioactive source through a gold plate - or whatever it was - observing that they could go through but that 1 out of 100 000 is deflected because of a collision with the nucleus.

(correct me if I'm wrong)

 

Now my question is... Alpha particles are positively charged and so the electrons in the gold plate should not let them through since they're attracted to them... What happened is exactly the opposite of that...The electrons made way for the alpha particles..(as we can see here: http://en.wikipedia.org/wiki/Image:Rutherford_gold_foil_experiment_results.svg)

Now I'm totally confused... This isn't working at all!

 

And also, what improvements did Bohr and Schrödinger do to the Rutheford theory?

[Cap'n Refsmmat]

The key is that the atom is so spread out that a few meandering electrons simply do not have the attractive power to stop a speeding alpha particle.

[hitmankratos]

So then, what is the problem with that theory?

And yeah... Electrons are always in orbit around the nucleus just like a fan around its center...So there's never any empty space.

[Gilded]

So then, what is the problem with that theory?

And yeah... Electrons are always in orbit around the nucleus just like a fan around its center...So there's never any empty space.

 

Actually there's a huge amount of empty space. The electron cloud around an atom isn't really dense at all in this sense, and as mentioned alpha particles have a velocity large enough to pass through a thin solid layer of atoms where very few collisions occur.

[hitmankratos]

So then where's the problem?

[big314mp]

That graphic really isn't very good at explaining, but I'll use the bottom image to make the point.

 

Rutherford saw most of the alpha particles go straight through. That means the atom is mostly empty space. Some were deflected at small angles, and some rebounded back at him. Those that were deflected indicated that there was something relatively immobile in the atoms, which implies a high mass. The fact that so few were deflected implies that this heavy object is very small. Thus, the Rutherford gold foil experiment provides evidence for the existence of the atomic nucleus.

[hitmankratos]

Ok then... What is the problem with Rutherford's model of the atom? Why did Bohr present something new?

[Cap'n Refsmmat]

Because Rutherford's (actually, JJ Thompson's) model did not predict a small, high-mass nucleus, like Rutherford's experiment showed.

Edited September 19, 2008 by Cap'n Refsmmat

[big314mp]

The difference that the Bohr model made, was that the electrons travel in quantized orbits. The rutherford model has the electrons just sort of orbiting the nucleus. However, a charged particle going in a circle will emit radiation, and lose energy (search "Synchrotron Radiation"). As the electron loses energy, it should spiral into the nucleus. So the rutherford model couldn't explain why electrons didn't just "fall" into the nucleus in a flash of light.

 

Bohr proposed that the electrons can only jump between certain orbits, and can therefore only absorb or emit photons with very specific energies. Therefore, an electron in the lowest orbit, can't emit any photons, so it can't lose any energy to spiral into the nucleus.

[insane_alien]

to simplify what big214mp said,

 

rutherfords model said there was a small heavy positive nucleus to an atom and a vague cloud of negative charge surrounding it, nothing more.

 

bohrs model improved on this by telling us how the electrons went around the nucleus(although this model only has a semblance of accuracy when applied to hydrogen, we have much better models now)

[Pradeepkumar]

originally posted by hitmankros

And yeah... Electrons are always in orbit around the nucleus just like a fan around its center...So there's never any empty space

 

you are wrong there when you throw a particle towards the fan it moves through the fan even if it rotates(sometimes missess-the particle should be very faster than the velocity of the rotation of the fan )try this in your home

 

thats the case with the atom also

when the alpha particles cross the electrons faster than the velocity of the electron it moves away from it due to the inertia.

thats why rutherford uses fast moving alpha particles

[Mr Skeptic]

Pradeepkumar, I advise against trying to tell others about things you don't know.

[Pradeepkumar]

sorry it was just a guess thats why i always use the sentence "correct me if am wrong'

[Mr Skeptic]

Now my question is... Alpha particles are positively charged and so the electrons in the gold plate should not let them through since they're attracted to them... What happened is exactly the opposite of that...The electrons made way for the alpha particles..(as we can see here: http://en.wikipedia.org/wiki/Image:Rutherford_gold_foil_experiment_results.svg)

Now I'm totally confused... This isn't working at all!

 

Perhaps this would make more sense to you if you knew that a single proton weighs in at 1,836 electron masses, and neutrons are a bit more. An alpha particle is two protons and two neutrons. Gold has only 79 electrons orbiting it, and they are fairly dispersed.

 

Now you can do the math.

[Klaynos]

The more mechanicsy questions/discussions/etc... have been moved to:

 

http://www.scienceforums.net/forum/showthread.php?t=35822