RULES OF OXIDATION NUMBER
ASSIGNMENT
STEPS IN ASSIGNNING OXIDATION NUMBERS
1) IF THE PERIODIC TABLE GIVES ONLY ONE OXIDATION STATE,
USE THAT THAT STATE. EXAMPLE Zn+2 .
2) APPLY THE RULES OF THIS POWERPOINT TO SOLVE FOR
OXIDATION NUMBERS OF ELEMENTS WITH MULTIPLE OXIDATION
STATES.
3) IF A MULTIPLE OXIDATION STATE ELEMENT HAS NO RULE,
ASSIGN IT A VARIABLE AND SOLVE USIMNG THE ALGEBRA
RULE(SLIDE 3).
THE SUM OF THE OXIDATION NUMBER (STATE ) OF EACH ATOM IN A
COMPOUND EQUALS THE CHARGE OF THAT COMPOUND.
KMnO4
GIVEN: K IS +1(GROUP 1 RULE ), O IS -2 (OXYGEN RULE)
Mn HAS MULTIPLE STATES(PERIODIC TABLE)
+1 + X + 4(-2) = 0
ALGEBRA RULE EXAMPLES.
Use group one to find other
elements.
Use group one as a known for
muli oxidation stare elements
Na2SO4
2(+1) + (X) + 4(-2)= 0
X = S = +4 each S
note: caution with
oxygen in binary
compounds
Li2O2
2(+1) + 2(X) = 0
X=O (oxygen) = -1
GROUP ONE ELEMENTS ARE ALWAYS 1+ IN COMPOUNDS OR AS FREE
(AQ) IONS.
Ex in NaCl EACH Na has an oxidation state of 1+.
in K2SO4 EACH K has an oxidation state of 1+.
A Li+1 (aq) free ion has an oxidation number of 1+.
GROUP ONE RULE EXAMPLES.
Use group one as a known for
Use group one to find other
muli oxidation stare elements.
elements.
Na2SO4
Li2O2
2(+1) + (X) + 4(-2)= 0
X = S = +4 each S
2(+1) + 2(X) = 0
X=O (oxygen) = -1 each
GROUP TWO ELEMENTS HAVE AN OXIDATION STATE OF 2+
IN COMPOUNDS AND AS FREE (AQ) IONS.
Ex in1) BaCl2 EACH Ba has an oxidation state of 2+
JJIBGO 2) In Ca3(PO4)2 EACH Ca has an oxidation state of 2+.
A free Mg+2 ION (AQ) has an oxidation state of 2+.
GROUP ONE RULE EXAMPLES.
Use group TWO as a known for
Use group TWO to find other
muli oxidation stare elements.
elements.
Ca3(PO4)2
3(+2) + 2(x) + 8(-2)=0
X = P = +6 each P
BaO2
1(+2) + 2(X) = 0
X=O (oxygen) = -1 each
ALL UNCOMBINED NEUTRAL (ELEMENTAL
STATE) ATOMS HAVE AN OXIDATION STATE
OF 0. THE NONPOLAR COVALENT
DIATOMOIC MOLECULES OF THE PERIODIC
TABLE ALSO HAVE AN OX# OF 0.
EX: Au0, Fe0, Na0, etc.
EX: H2, O2, N2, Cl2, Br2, I2, F2 are3 all in the 0
oxidation state
THE OXIDATION NUMBER OF IONS IS THE
IONIC CHARGE.
EX: Au+2 = 2+, Fe+3 = 3+, Na+ = 1+, etc.
EX: NO3 -
HAS AN OXIDATION NUMBER OF 1- FOR THE (EACH) POLY
ATOMIC ION GROUP.
THE OXYGEN RULES: Each oxygen USUALLY
has an
oxidation state of 2- in compounds, 0 in O2.
USE CAUTION IN BINARY
COMPOUNDS OF OXYGEN AND
EX, in H2O oxygen is 2HYDROGEN -- CHECK FOR RULE
In H2SO4 EACH oxygen is 2EXCEPTIONS.
IMP -- EXCEPTION #1– when oxygen is contained in a PEROXIDE, it
has an oxidation state of 1-.
PEROXIDES - contain the peroxide ion (O2-2), EACH oxygen is 1-.
- peroxides are when 2 group one elements combine with the peroxide ion
H2O2, Li2O2, K2O2 are peroxides, each O is 1BaO2, CaO2, MgO2 are peroxides, each O is 1-
IMP -- EXCEPTION #2 – when oxygen is combined with FLOURINE,
its oxidation state is 1+ or 2+. Fluorine is electronegative enough to
oxidize oxygen.
EXAMPLE :
in FO the oxygen is +1, in F2O each oxygen is 2+
Fluorine is always 1in its compounds
THE HYDROGEN RULE:
THE OXIDATION STATE OF HYDROGEN IS USUALLY 1+
EX in H2O each hydrogen is 1+
IMP-EXCEPTION – in GROUP 1 METAL HYDRIDES the
hydrogen is 1-, hydrogen is electronegative enough to oxidize
group one metals.
EX: NaH, KH etc the hydrogen is 1USE CAUTION IN BINARY
COMPOUNDS OF OXYGEN AND
HYDROGEN -- CHECK FOR RULE
EXCEPTIONS.