Sulfate is a covalent ion. For this reason it"s much more realistic to use formal charges, not oxidation states, to define its atoms.
It"s yes to give sulfate one overall oxidation state, yet it doesn"t make feeling to carry out so for sulfur and also oxygen in sulfate.
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OXIDATION STATE APPROACH: best IONIC BONDS
Oxidation states are theoretical charges because that a compound that has actually ideal ionic bonds, or would type ideal ionic bonds, i.e. complete transfer of the electron pair to just one atom in the bond.
You created #"SO"_4^(2-)#, i beg your pardon is the sulfate polyatomic ion. You created that its total charge was #-2#.
Since sulfate (#"SO"_4^(2-)#) is currently ionized, its fee is its oxidation state. So it"s type of meaningless to uncover the "oxidation state" for #"SO"_4^(2-)# since it"s already given.
The oxidation says for sulfur and also oxygen atom are figured out from:electronegativitiestotal charge
#"SO"_4^(2-)# has actually a complete charge of #-2#, and also oxygen is more electronegative than sulfur. So, oxygen polarizes the electron thickness towards itself more, and thus has actually the more negative oxidation state here.
Since oxygen is on column 16, its expected oxidation state is #color(red)(-2)#. Therefore:
#-2xx4 + x = -2#
#=>##x# offers the oxidation state that sulfur, which is #color(red)(+6)#.
But store in mind the this is unrealistic. If you ever do this because that redox balancing, it"s only an audit scheme, and nothing more.
FORMAL fee APPROACH: right COVALENT BONDS
#"SO"_4^(2-)# is mainly a covalent ion. The electronegativity differences are just #1.0#. So, it"s much more practical to discover the formal charges.
Formal charges are the theoretical partial charges because that if the compound has actually ideal covalent bonds, i.e. perfectly also sharing the electron pairs.
When we cleave each bond in half, us then assume the one electron walk to every atom, and we have the right to assign official charges the way.
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Then:The "owned" electrons are the people the atom has actually upon this cleavageThe "valence" electrons room the ones that the atom typically has actually as a neutral atom.