For an atom that becomes an ion, does it have a formal charge, or net charge? What is the difference between formal charge, oxidation state, and net charge?
1 Answer
Jul 21, 2016
For an atom that just became an ion, like
Formal charge is the hypothetical charge for an atom when assuming that electrons are perfectly evenly shared in a chemical bond.
It's not the same as an oxidation state; it's pretty much the complete opposite.
- Strictly speaking,
#"O"^(2-)# doesn't have a formal charge because it's not within the context of a molecule. - In
#"CO"_2# , we have#:stackrel(..)"O"="C"=stackrel(..)"O":# . The formal charge on#"C"# is#0# , and the formal charge on each#"O"# is#0# . We can say that because the atoms are in the context of a molecule.
Oxidation state is the hypothetical charge for an atom when assuming that electrons would be completely transferred from one atom to another in a chemical bond.
- If you look at a lone atom, its charge is its oxidation state. The oxidation state of the
#"O"^(2-)# anion is#color(blue)(-2)# , the same as its charge,#2-# . - The oxidation state of
#"O"# in#"CO"_2# would be#-2# , so the oxidation state of#"C"# in#"CO"_2# would be#+4# . We write that as#stackrel(+4)("C")stackrel(-2)("O"_2)# . It does not mean that carbon has given away all of its#n = 2# valence electrons.
Net charge is simply the total charge on an atom or molecule or compound.
- For
#"O"^(2-)# , it's only one atom, so its net charge is its actual charge,#color(blue)(2-)# . - For
#:stackrel(delta^(-))("C")-=stackrel(delta^(+))("O"):# , the net charge is#0# , because the formal charge on#"C"# is#-1# , and the formal charge on#"O"# is#+1# , so#-1+1 = 0# .
