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Chemistry oxidation question

im sooo confusedd
oxidation numbers of SiO2 is apparently +4 for Si and -2 for O but i don't understand since i thought if you had O2 the oxidation state would be -1 therefore Si would be +2

Reply 1

mildhan

Original post by May1200

im sooo confusedd
oxidation numbers of SiO2 is apparently +4 for Si and -2 for O but i don't understand since i thought if you had O2 the oxidation state would be -1 therefore Si would be +2

Oxygen always has an oxidation state of -2, unless bonded to fluorine, or in oxygen gas, where the oxidation state is 0. It has to do with electronegativity, just remember it. Si has to have an oxidation state of +4 because there are 2 x O (so -4 in total). SiO2 has no overall charge, so the oxidation state of Si must be +4.

Reply 2

May1200

Thank you! and i thought there was a rule about oxygen being -1 if it was peroxide or something, how do you tell if its a peroxide?

Original post by mildhan

Reply 3

JzANonM

you can tell if its a peroxide if the formula is something like O2X2
so H2O2 is hydrogen peroxide eg

Reply 4

mildhan

Original post by May1200

Thank you! and i thought there was a rule about oxygen being -1 if it was peroxide or something, how do you tell if its a peroxide?

Yes, that is a rule. Oxygen has an oxidation state of -1 in peroxides. Otherwise oxygen generally has an oxidation state of -2 besides the other occasions mentioned previously.