I'm no chemist, so bear with me.

From my understanding, the reason metal oxidation occurs is because the metal is losing electrons to the oxygen ions in the air; and that an ion is an atom or molecule which either has more or less electrons than the "standard" of that atom/molecule; which is why it's "taking" electrons from something else.

What prompts my question has to do with soldering. I'm learning that one reason for the use of flux is to prevent this oxidation and protect the soldering tip. So according to what I said before, a soldering iron becomes oxidized because it has lost electrons to the air, and the high temperatures hasten this process.

Now to get to the detailed question: I understand the very basic oxidation process. But, once the metal has lost electrons, doesn't that now make it composed of ions? If so, Why does the metal continue to corrode? Why isn't the metal now taking electrons and virtually "restoring" itself? What is it about oxygen ions that make them the ones that take electrons from metals such as copper? Why isn't copper the one taking electrons from the air? Does it have to do with valence electrons or electron shells or something?


1 Answer 1


When a metal like iron is oxidized, each iron atom loses 3 electrons. These electrons are kept by oxygen atoms from the air. The iron atom becomes an ion charged 3+, and the oxygen atom becomes an ion charged 2-. The positive ions still attract negative ions, and they will never separate. Two iron ions and three oxygen ions are necessary to make a new compound which must be not charged. This assembly is a new substance called rust, which has a brown color. Once such a transformation has happened, the next iron atoms can repeat this operation : the amount of rust will slowly increase.

All metals can be oxidized by more or less the same way. But it could be quicker or longer. For copper, this reaction is not so frequent. Copper makes a copper oxide which is black, but you may wait for months to see it.

  • 1
    $\begingroup$ Patina isn't black and rust isn't Fe2O3. BTW treating such compounds as bare ions was what get OP confused in the first place. $\endgroup$
    – Mithoron
    Nov 12, 2019 at 21:13

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