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Author Topic: What's in the space between atoms ?  (Read 8348 times)

Offline neilep

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What's in the space between atoms ?
« on: 02/05/2005 19:03:50 »
I am wondering if this is a very very easy question, which just shows my  ignorance but does demonstrate my curiosity.....as I assume that there is a force keeping the atoms close together eh ?..any chance of a laymans answer please ? and is it the same force that keeps electrons and stuff whizzing around the nucleus ?

Thanks

Neil


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Offline daveshorts

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Re: What's in the space between atoms ?
« Reply #1 on: 02/05/2005 19:34:25 »
It is the same force which holds electrons around the nucleus that holds atoms together - the electric force.

A simplified view of what is happening is that:
 the atoms nuclei are positive so repell each other
the electrons are negative so repell each other and are attracted to the nuclei

 think of the situation where you have new hydrogen nuclei with an electron between them:
Code: [Select]
 +       -       +
   <--d--> <--d-->
The electric force is an inverse square force like gravity so the closer things are together the greater the force. The nuclei are closer to the electron than they are to the other nucleus, so the attractive force to the electron is greater than the repulsive force with the other nucleus.

The electron is not allways in the middle so they don't collapse in on one another, and if the nuclei get too close together the  electron is between them for less of the time, so the repulsive force starts to dominate. This means that there is a stable distance they want to be at.

This is all somewhat simplified as I have tried to ignore quantum effects, but I think it gives the basic idea.
 

Offline neilep

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Re: What's in the space between atoms ?
« Reply #2 on: 02/05/2005 20:57:38 »
Thanks Dave, I appreciate the simplified answer. This electric force that holds atoms together, what is that comprised of ?..or is that getting to the quantum state of things ?...

thanks

neil


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Offline moth

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Re: What's in the space between atoms ?
« Reply #3 on: 03/05/2005 18:09:10 »
In classical physics, fields are not explained in terms of anything else, so atoms are made up of a bunch of point particles (electrons) buzzing around a nucleus which is itself made up of point particles (neutrons and protons which in turn are built from quarks, which are point-like as far as we can tell), and all the rest is empty space through which these mysterious fields propagate.

Even Newton thought that the idea of fields that act at a distance must be leaving something out, but you do have to get into quantum physics to see what.

Quantum Mechanics is all about waves of (rotating complex number valued) probability spreading out from the initial conditions. When you want to work out (say) the location of a particle you add together all the waves and square the result to get the probability distribution for the particle's location. The rotating complex number nature of the waves means they interfere in interesting ways. But physicists like thinking about particles so have found ways describing QM in terms of particles that mostly behave as expected, plus some rules to take care of everything really being waves underneath. (Richard Feynman's book 'QED: The Strange Theory of Light and Matter' gives a really readable account of how this works.)

(edit: i should clarify, neither the waves or the particles picture quite fits well enough to be considered more fundamental. Both have their uses and their oddities.)

The key quantum rule we need here is Heisenberg’s Uncertainty Principle which (among other things) allows physical systems to pass through states that don't conserve energy by paying a probability penalty proportional to the size and duration of the energy discrepancy. This means that the electrons and protons in an atom can emit photons without giving up any of their own energy provided these photons are quickly adsorbed again, potentially by a different particle. These virtual photons carry real momentum between the particles and can be viewed as creating the electric force.

There is a well-known analogy with people on skates throwing a ball from one to the other. Each time they throw or catch the ball, conservation of momentum means that they are accelerated away from the other person. Even though they are out of reach of each other, they are pushing each other away by using the ball to exchange momentum. Unfortunately this analogy doesn't help you see how virtual particle exchange can lead to attractive forces. Basically you have to give up on simple explanations with particles and examine what the quantum mechanical waves are doing. This seems like a good explanation, but it is pretty heavy going:

newbielink:http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html [nonactive]

Another consequence of the small-scale violation of energy conservation is that empty space isn't so empty, but teeming with particle-antiparticle pairs that borrow energy to pop into existence for a few moments before annihilating and repaying the energy. Google for the 'Casimir effect' for some of the consequences of this.
« Last Edit: 04/05/2005 21:41:41 by moth »
 

Offline neilep

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Re: What's in the space between atoms ?
« Reply #4 on: 04/05/2005 22:48:33 »
Thomas, thank you very much for your response. I'd be telling 'porkie pies' if I said I understood every word, but with your clarity of language...I'm getting there. Perhaps I need to wear a white coat and have a leaking pen in my pocket :-)

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Offline gsmollin

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Re: What's in the space between atoms ?
« Reply #5 on: 06/05/2005 03:15:36 »
That pen ruined my favorite shirt!
 

Offline neilep

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Re: What's in the space between atoms ?
« Reply #6 on: 06/05/2005 08:54:59 »
quote:
Originally posted by gsmollin

That pen ruined my favorite shirt!



I've been up all night and feel totally shattered but Mr Gsmollin put a smile on my face....thank you sir.:)

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Re: What's in the space between atoms ?
« Reply #6 on: 06/05/2005 08:54:59 »

 

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