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Thread: Ionization Energy

  1. #41
    Registered Senior Member chikis's Avatar
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    Quote Originally Posted by Nasor View Post
    That's a picture of "VFI" atomic radii, which is based on data related to the length of the covalent bonds that the elements form when they're part of a molecule. The VFI method of determining atomic radii works fairly well for elements that actually take part in covalent bonding, but is not a useful way to determine the atomic radius for noble gases, since they only form very very weak covalent bonds. The stronger a covalent bond, the shorter it will be. Strong, short covalent bonds normally go hand-in-hand with short atomic radii, which is why the VFI method of measuring radius works well for elements other than noble gasses. Any attempt to determine the atomic radius of a noble gas with the VFI method will be skewed by the fact that noble gasses only form very very weak (and therefore very long) covalent bonds.

    Note that this was partly explained in the text at the bottom of your picture: "These data are based on interatomic distances in the structures of the elements."

    Pete's chart, and probably whatever hypervalent_iodine wanted to link to, suffer from the same problem. Although Pete's chart doesn't actually say how the radius values were calculated, I would bet money that it is also VFI radii, or some similar method that depends on bond length.

    Here is another link from the same source as your graphic:http://www.crystalmaker.com/support/...dii/index.html

    Go down to the bottom and look at the actual numbers for atomic radii. You'll see that the radii decrees all the as way across the row from left to right, with no discrepancy for the noble gases.

    Edit: If anyone here believes that the noble gasses really have a smaller atomic radius (by which I mean the average distance from the nucleus to the valence electrons), I defy you to provide a coherent explanation of why that would be, especially considering Slater's rules...
    I now realise my mistake, you are very correct. Am begining to come to my senses. Initialy whenever the word radi is mentioned, what comes to my mind is nothing but atomic radi. I never knew there are diffrences. I used to think that ionic, vandawal, atomic and convalent and metallic radi are all the same. But in this thread am discussing atomic radi. All the same, I say thank you for the awareness.
    I now accept that atomic radi decreases left to right across a period thus the nobles gases being at the extrem right of each row should have the smallest atomic radi. Thanks am now cleared.
    Last edited by chikis; 04-14-12 at 07:31 PM.

  2. #42
    Registered Senior Member
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    the thing about noble gases having a larger atomic radius is in our book too. infact, they claimed noble gases have almost twice the radius as the halogen before them. hat i think they mean is that it is that way when you take inter molecular (atomic distance) distance between them... but it still doesnt make sense because they clearly mentioned that the reason for their big size is inter-electron repulsion because there are just "too many" electrons in there and they dont like each others' company much.
    can anyone plz tell me more on this?
    thanks

  3. #43
    hobnob with the flash mob Aqueous Id's Avatar
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    Quote Originally Posted by rohIT View Post
    the thing about noble gases having a larger atomic radius is in our book too. infact, they claimed noble gases have almost twice the radius as the halogen before them. hat i think they mean is that it is that way when you take inter molecular (atomic distance) distance between them... but it still doesnt make sense because they clearly mentioned that the reason for their big size is inter-electron repulsion because there are just "too many" electrons in there and they dont like each others' company much.
    can anyone plz tell me more on this?
    thanks
    I think if you dig into this a little deeper you will begin to understand that the idea of a "radius" comes from the old idea that atoms are little spheres which isn't correct. The shell is a region of probable occupation by the electron, not an actual surface of definitive shape.

    Check out the various ways we refer to atomic radius under "Definitions" at

    http://en.wikipedia.org/wiki/Atomic_radius

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