What is the oxidation number of oxygen in #"sodium peroxide"#, #Na_2O_2#?
In sodium peroxide the oxidation state of oxygen is
When we assign oxidation numbers, we assign conceptual charges to the individual atoms such that when these charges are summed up we get the charge on the molecule or the ion. Thus, elements have an oxidation number of
For your sodium peroxide we have
Another way of looking at this is to consider the peroxide ion itself,
And thus the oxidation state of oxygen in peroxide is conceived to be
The Oxidation of state of Oxygen in
The structure of the the molecule sodium per oxide is with each sodium joined to one oxygen and the two oxygen joined with one bond to each other and the other bond to the sodium atoms.
The bond that Oxygen shares with Sodium does change the Oxidation state of both Sodium and Oxygen. Sodium with a much lower electronegativity will give up one electron to the Oxygen becoming +-1 ( Sodium is oxidized) The Oxygen having a much high electronegativity will take an electron from the Sodium becoming (-1) The Oxygen is reduced.
Na : O :
This Lewis dot structure shows the "shared" electrons between the the Sodium and Oxygen atoms which results in the transfer of an electron from the Sodium to the Oxygen resulting in the +1 charge for Sodium and the -1 charge for Oxygen. The shared electrons between the two Oxygens results in no loss or gain of electrons.