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Every explanation I can find says something like: valence electrons in metals have low ionising energies and non-metals ''want'' to complete their valence shell.

But I can't seem to get my head around the ''wants to complete it's valence shell'' force.

Take a neutral sodium atom and a neutral chlorine atom separated by some distance. Now move them closer until the valence electron of sodium makes the jump. What force did it feel if chlorine is neutral ? My only explanation is that the valence electron induces a dipole on the chlorine atom. In other words the presence of the valence electron pushes the electron valence orbital of chlorine away slightly. The positive nucleus of the chlorine atom is not pushed away due to shielding by the other shells in chlorine. Now that the valence shell of chlorine is pushed away slightly the valence electron of sodium begins to feel a slight attraction to the chlorine atom despite it being neutral overall. It is now a dipole. At some point the force of attraction between the valence electron of sodium and the chlorine atom is stronger than to the sodium atom and makes the jump.

Is this a reasonable explanation as to why the electron makes the jump or is it something else entirely ?

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    $\begingroup$ Have a look at the energy cartoon for potassium and fluorine: chemistry.stackexchange.com/a/128771/79678. As K and F atoms get closer and closer, it is energetically very favorable for ionization to happen. So it happens. $\endgroup$
    – Ed V
    Apr 7 at 17:07
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    $\begingroup$ Ionic bonding doesn't really work like that, so believe in any "lies to students" you like. $\endgroup$
    – Mithoron
    Apr 7 at 17:11
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    $\begingroup$ @Mithoron. What do you mean ? Where are these "lies to the students" ? $\endgroup$
    – Maurice
    Apr 7 at 20:34
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    $\begingroup$ Ionisation energy of Na is greater than Cl electron affinity. So it is endothermic process, unless the energy balance is supported by releasing of energy of ion hydration energy , or of the ionic lattice energy. $\endgroup$
    – Poutnik
    Apr 7 at 21:18
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    $\begingroup$ Also is worth nothing that they are not simply getting Na+ and Cl-. Technically they stick togheter. In other words, at the distance involved in your phrasing, the electrons of both elements are in a field which is due to both nuclei. If you visualize it like this it might look less magic. The "want" must be taken in the right scenario, a new substance is formed. For how the filling of orbitals works and the energy that result is, I am not ashamed to say that there is quite a mystery. But it is how it works. The forces are electromagnetic in nature, but this is just easy to be said. $\endgroup$
    – Alchimista
    Apr 8 at 11:10

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