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Topic: Regarding Atomic Radii  (Read 4453 times)

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Cletis

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Regarding Atomic Radii
« on: November 20, 2004, 11:59:43 PM »
I am very pleased to have found this place. I have been reading the posts here and both patrons and moderators seem knowledgeable. I have just a couple of questions that input would be appreciated on. My knowledge is basic (I only have 2 or 3 books on the subject and after thorough reading none answer my question sufficiently) so please bare with me.

1.) I am not sure if i understand this concept correctly, or if there is more to it. Elements starting at the left of the table in a particular row get progressivly smaller as you move towards the right despite the additional neutrons and protons. I understand that this is largley because of the larger electrostatic force generated by the nucleus, but is this the whole story? ??? It seems there must be some addition force at work here. Along similar lines with cations and anions. If an atom loses an electron the corresponding cation is smaller due to the larger electrostatic force being distributed over the rest of the atom and the opposite for the anion.

2.) Anti-bonding?? I dont understand this at all. Is there an anti-bonding pair for every single bonding pair? If so is this exclusive for sigma or pi bonds?

 Any info you all could shed on this would be fantastic!

Offline Mitch

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Re:Regarding Atomic Radii
« Reply #1 on: November 21, 2004, 01:53:59 AM »
1.) You understand the concept just fine. Just keep thinking about the concept and playing with it in your mind, until you understand it better.

2.) A region where electrons overlap with each other is just called a bond. A region where no electrons overlap will be called antibonding. Typically for every bond there will be an antibond, but this doesn't neccessarily mean there will be electrons in the antibonding region.
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Cletis

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Re:Regarding Atomic Radii
« Reply #2 on: November 21, 2004, 01:54:31 PM »
Wow, those electrostatic forces are greater than i realized. I always pictures them as a relatively weak influence, but now it seems quite the opposite. Which makes sense now that I think about it. Electrostatic forces are probably the greatest of all in the intra-atomic realm. They are a form kinetic energy correct? Are these forces responsible for the vibrational and rotational energy of the atom? I understand how these effect the electron paths but what causes the vibration of the whole. Are the main two forms of kinetic energy from an atom electrostatic and heat ?

I dont mean to bombard with questions but I cant express how exiting it is to have someone to talk to about the wonderful world of chemistry. I am self taught and none of my friends or relatives are really intersted and I dont live by a school. So in the past when I would have a question it was either the library or rereading. Its just nice to have this resource and I will contribute where i can. :)

I think you may have actually cleared up the whole anti-bonding confusion for me. I was just looking at it the wrong way as usual. lol . So lets say for instance we have little old p-orbital from carbon with one of its lobes filled with a -spin(down) electron. When an hydrogen atom with a half filled s-orbital with a +spin(up) comes along and the two interact if favorable, the +spin from the hydrogen fills the empty space in carbons p-orbital thus filling it. now the +spin electron is the one in the bond and -spin electron would then become the anit-bonding pair?. I was just using this as an example so please correct me if im wrong.

Thanks.

« Last Edit: November 21, 2004, 01:57:32 PM by Cletis »

Offline Mitch

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Re:Regarding Atomic Radii
« Reply #3 on: November 21, 2004, 02:44:10 PM »
Electro"static" force are a form of potential energy.

Vibrational and rotational energy is a more complicated situation and I would suggest reading a p-chem book in order to make it make more sense.

As far as the antibonding question goes, I think you now know too many theories of bonding and are starting to confuse them. I'll pick MO theory to answer you since bonding and antibonding orbitals come from MO theory. Regardless of the spin of the electrons, prior to joining, they will always be placed in the bonding orbital. If you have more than 2 electrons, then they will start to fill the antibonding orbital. And of course in a bonding orbital the electrons are paired and of course in an antibond the spins are unpaired.
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