Question: How do you find the oxidation state of an element?
Answer:
Oxidation numbers are the effective charges
that atoms have when they form chemical compounds. For example, if
you have iron (III) oxide, the charge on iron is +3. Oxidation numbers
are used in various ways. First of all, they're used in finding the
chemical formulas of various compounds. They're also used in finding
the
products of various chemical reactions,
particularly electrochemical/redox reactions.
To find the oxidation numbers of many elements,
take a look at the periodic table and figure out how far they
are from the nearest noble gas.
Alkali metals and alkaline earth metals have +1 and +2 charges, respectively,
because they need to lose one and two electrons to be like the nearest
noble gases. On the other side of the periodic table the same thing
happens, except that the oxidation numbers are negative - that's why halogens
typically have a -1 oxidation number.
For other elements, you determine the oxidation
number by determining the oxidation numbers of elements that
are easier to figure out (such as halogens,
alkaline earth metals, etc) and the fact that compounds are neutrally charged.
For example, in CuF2, the oxidation numbers of each fluorine
atom are -1, meaning that both fluorine atoms together have a charge of
-2. Since the compound must be neutral, the
charge on copper must be +2.