How does something like elemental oxygen oxidize anything if each atom's valence shell is full? [duplicate]








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[Why is oxygen an oxidizing agent?](/questions/90773/why-is-oxygen-an-oxidizing-agent)

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Been learning in biology about $\ce{O2}$'s role as an oxidizing agent, but I don't really understand how $\ce{O2}$ can take electrons from anything if it's not reactive....




Most compounds consist of atoms that have "filled" their valence shells. It is basically what defines "reasonably" stable molecules. That does not mean that they cannot react with other molecules. Nature always seeks to find the lowest energies possible for its molecules, and the oxygen molecule has a very high potential energy. 


The oxygen molecule is like two bullies who live together. They'd rather find a pair of victims that are weaker than themselves, split up and live an abusive but for them good life alongside their weaker partners. There are worse compounds out there, like the homicidal maniac [Chlorine Trifluoride](https://en.wikipedia.org/wiki/Chlorine_trifluoride) who will rip apart the stablest of marriages to abominable and atrocious results.


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