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Thread: How much energy/force would it take to move an atom it's own diameter?

  1. #1 How much energy/force would it take to move an atom it's own diameter? 
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    How much energy/force would it take to move an atom the distance of its own diameter? I have been using 150pm as the width of the atom in question, because I assume that is about the average for an atom on earth. Please answer in decimal form, with larger units.


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    exchemist
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    Quote Originally Posted by Nikola Tesla View Post
    How much energy/force would it take to move an atom the distance of its own diameter? I have been using 150pm as the width of the atom in question, because I assume that is about the average for an atom on earth. Please answer in decimal form, with larger units.
    This is a bit of a "How long is a piece of string" question, because it all depends on what forces, if any, keep the atom in question in its current position.

    In a low pressure monatomic gas, there is effectively no force at all required, as the atoms are free-floating. In a crystalline solid, it depends on the strength of the bonding between atoms.

    The diameter of an atom is not well defined, as the electron cloud peters out asymptotically, a bit like the top of the Earth's atmosphere. In chemistry, we often use notional "atomic radii", averaged from typical interatomic distances in crystals and molecules. There is more about this here: Atomic radius - Wikipedia, the free encyclopedia

    As to energy required to move an atom by its diameter, if we take the simplest bound system (i.e. as opposed to something like a monotomic gas), the hydrogen molecule, there is a nice potential well diagram for one here: Bond Lengths and Energies

    You can see from this the energy is at a minimum at the "normal" interatomic distance and if you compress the bond or stretch it, the energy goes up, i.e. you have to do work on it. Doubling the interatomic distance would be equivalent to moving each atom by a distance equal to its radius, or to moving one atom by its diameter if you like. It looks to me as if this will take you to a point 2/3 or 3/4 up the right hand side curve of the potential well.

    The depth of the potential well is the "bond energy". For H-H this is (from the same link) about 400kJ/mol, of the order of 4eV per molecule. You need to put in about 2/3 or 3/4 of this amount to stretch it by one atomic diameter.

    But with different atoms, molecules, crystals etc, different numbers will apply.

    Hope this helps but happy to discuss if needed.


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