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A saturated force

  1. Aug 17, 2010 #1
    My lecturer writes the following in his lecture notes:
    " In an ionic bond, the force is not saturated so that one ion bonds to many near neighbours (as many as packing will allow) "

    What does saturation mean in this context?

    Clearly, the binding force is largely due to the electrostatic force and not gravitational, right? This is because the electrostatic force between two particles is much much stronger than the gravitational force ??

    Finally, how does a lack of saturation allow one ion to bond with as many neighbours as packing will allow? And what exactly does packing mean in this context?

    Any help will be greatly appreciated!
     
  2. jcsd
  3. Aug 19, 2010 #2
    In an ionic bond, the attraction between ions is purely electrostatic, which is a long-range force. That means it is quite difficult for other ions clustering around to completely shield the charge and neutralise it. In fact, the main constraint on the number of ions clustering is just the geometrical question of actually fitting them into the space available - that's 'packing'. There are several types of packing (or stacking) patterns that might form , which are energetically more favourable (which makes them more likely) than a random pattern.

    On the other hand, other forms of bonding rely on a different mechanism - like sharing a single electron between their orbitals. That's a short-range force - it's confined essentially to the two atoms involved.
     
  4. Aug 20, 2010 #3
    Thank you! You mentioned that "it is quite difficult for other ions clustering around to completely shield the charge and neutralise it.". To what degree, nonetheless, will the surrounding ions shield the charge in an attempt to neutralise it?


    "There are several types of packing (or stacking) patterns that might form , which are energetically more favourable (which makes them more likely) than a random pattern." : Why would any physical system want to minimise its total energy? Also, the total energy must surely be expressed with respect to some reference frame. What if the energy changes randomly as we shift from one reference frame to another? Surely then, the total energy if minimised w. r. t. one reference frame could possibly be greater if looked at from another reference frame !!??

    "On the other hand, other forms of bonding rely on a different mechanism - like sharing a single electron between their orbitals. That's a short-range force - it's confined essentially to the two atoms involved." : I thought all forms of bonding involve electrostatic forces, and electrostatic forces are long-range. So, I can't understand how the covalent bonding is due to a short range force?

    Thank you for your help!
     
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