## Maximum oxidation number

Antonio Melgoza 2K
Posts: 33
Joined: Fri Sep 25, 2015 3:00 am

### Maximum oxidation number

How do you find the maximum oxidation number of an element?

Chem_Mod
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### Re: Maximum oxidation number

For cations, typically it is equal to the number of valence electrons.
For example:
Li --> Li+
Mg --> Mg2+
Al --> Al3+

For anions, typically it is equal to the number of electrons to obtain an octet.
O --> O2-
Cl --> Cl-

Christopher Ansay 1C
Posts: 28
Joined: Fri Sep 25, 2015 3:00 am

### Re: Maximum oxidation number

You can find the maximum oxidation number of an element by first identifying how many valence electrons there are for that element. There was one homework problem in the book (3.23) asking for the maximum positive and maximum negative oxidation numbers for chlorine. Chlorine has 7 valence electrons (2 from the 3s subshell and 5 from the 3p subshell). The maximum number of electrons it can lose to become positive is 7 electrons. It cannot lose electrons from its 2p and 2s shells because these are part of its core and requires too much energy to remove. So a chlorine without all 7 of its valence electrons is Cl^7+. That is its maximum positive oxidation number.
Its maximum negative oxidation number is the max electrons it can gain to become negatively charged. Chlorine has 5 electrons in its 3p subshell. To complete a "p" subshell, an element needs 6 total. In order to do this, chlorine will gain 1 electron from a bond and will stop at 1 extra electron because it will complete its outermost shells. Chlorine with 1 extra electron is Cl^-. That is its maximum negative oxidation number.