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In the first step of formation of rust in iron, there is something that pulls electrons from the iron lattice, resulting in the formation of $\ce{Fe^{2+}}$. The reaction is:

$\ce{Fe -> Fe^{2+} + 2e-}$

After that positive iron is repelled from the lattice, it is dissolved into water and a lot of reactions take place.

What is the thing that pulls the electrons from iron? (I guess it must be something positive, right?)

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    $\begingroup$ This is only "half-reaction" by no means description what really happens. $\endgroup$ – Mithoron Jul 14 '17 at 14:01
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The iron is being oxidized in this process. You just need something to act as an oxidizing agent. Dioxygen will do quite nicely:

$$\ce{O2 + 4e- -> 2O^{2-}}$$

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  • $\begingroup$ how $\ce{O2}$ does that? if $\ce{O2}$ is not negative, how can it attract electrons? $\endgroup$ – Henrique Rigitano Jul 14 '17 at 14:56
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    $\begingroup$ Iron isn't negative but it can give up electrons. Shouldn't the opposite also be true? It's not so much that the oxygen attracts electrons. It's just that electrons are more stabilized when they're with oxygen than with iron. $\endgroup$ – Zhe Jul 14 '17 at 15:21

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