p232234 Assigning Oxidation Numbers Oxidation Number positive or negative number assigned to an atom according to a set of rules Rules for Assigning Oxidation Numbers The oxidation number of ID: 358653
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Slide1
Oxidation Numbers
p.232-234Slide2
Assigning Oxidation Numbers
Oxidation Number
: positive or negative number assigned to an atom according to a set of
rulesSlide3
Rules for Assigning Oxidation Numbers
The oxidation number of
any free element
is 0
- Na or O
2
The oxidation number of a
monatomic ion
is equal to the charge on the ion. Some atoms have several possible oxidation numbers.
- Iron can be Fe
2+
or Fe
3+
Slide4
Rules for Assigning Oxidation Numbers
The oxidation number of each
hydrogen
atom in most of its compounds is +1,
EXCEPT
in metal hydrides (
LiH
) where it is -1.
The oxidation number of
oxygen
IN A COMPOUND
is -2, EXCEPT in peroxides (H
2
O
2
) where it is -1.Slide5
Rules for Assigning Oxidation Numbers
The sum of the oxidation numbers of
ALL THE ATOMS
in a particle must equal the apparent
charge
of that particle.
SO
4
2-
, S
2
O
3
2-
, Na
2
SO
4
In compounds, the elements of Group 1, 2, and aluminum have positive oxidation #’s of +1, +2, and +3 respectively.
AlBr
3
,
CaOSlide6
Now you try some!
Find the oxidation numbers of
iodine
in HIO4
, HIO
3
, HIO,
HI
Section Review p. 235 #1 a-
iSlide7
Oxidation-number Changes in Chemical Reactions
If the oxidation number increases for an atom
Oxidation has occurred
If the oxidation number decreases for an atom
Reduction has occurred
2AgNO
3
(
aq
) + Cu(s)
Cu(NO
3
)
2
(aq) + 2Ag(s)What is being oxidized? What is being reduced?
+1 +5 –2 0 +2 +5 –2 0Slide8
Now you try some!
Use the changes in oxidation numbers to identify which atoms are oxidized, and which atoms are reduced:
2H
2
(g) + O
2
(g)
2H
2
O (l)
2KNO
3
(s) 2KNO
2
(s) + O2 (g) NH
4
NO
3
(s) N
2
(g) + 2H
2
O (g)
(
HINT
: consider each N separately)
PbO
2
(
aq
) + 4HI (
aq
) I
2
(
aq
) + PbI
2
(s) + 2H
2
O (l)