general question with oxidation/reduction

[yoyohomieg5432]

In a combustion reaction such as CH4 + O2 -> CO2 + H2O, how is oxygen reduced? I understand that the oxidation state of oxygen goes from 0 to -2, obviously meaning it was reduced, but physically what is happening? I don't see how oxygen "gained" electrons. In both cases it has a full octet of electrons and no formal charge whether in O2 or H2O.

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[sazerac]

O2 is a covalent double bond. Oxygen has four electrons of its own, and four it shares equally with that other oxygen. It splits those shared electrons 50 50 so in sum total it's outer shell only has six whole electrons.

With H2O the oxygen is a big bully and damn near STEALS the electrons from the hydrogens. So the oxygen has 8 electrons if its own, and each hydrogen has ZERO according to "oxygenation number" math.

When you are doing oxygenation number math all the electrons are assumed to go to the more electronegative atom.