Transcript oxidation number

Chapter 10
Oxidation Numbers
Oxidation Number
• The oxidation number is the charge on a
single atom.
Oxidation Number
• The oxidation number is the charge on a
single atom.
• Examples:
Na+ (oxidation number = +1)
Clˉ (oxidation number = -1)
Al3+ (oxidation number = +3)
O2ˉ (oxidation number = -2)
We can use the periodic table to
determine oxidation numbers.
Determining Oxidation Numbers
• Metals form positive ions (7+ is the
highest positive oxidation number).
• Nonmetals tend to form negative ions.
• However other than the noble gases
which have a zero oxidation number
and fluoride (F-) which is always -1, all
other nonmetals could have positive
oxidation numbers as well.
We can use the periodic table to
“predict” oxidation numbers
• If we have the name of the ion a
“prediction” is unnecessary.
• Potassium ion
• Iron (II)
• Nitride
• We can often predict the range of
oxidation numbers of the positive
monatomic ions other than groups 1 & 2,
Ag, Cd, Zn, and Al.
• The periodic table can often be used to
make a quick prediction as to possible
range of oxidation numbers of cations
outside groups 1 & 2 Ag, Cd, Zn, and Al
What common ions can Iron form?
Often the electron configuration can help us to
understand why certain oxidation numbers form.
Fe +2
Fe +3
Most transition metal elements have more than one positive
ion. (However +2 is the most common oxidation number for
metal ions).
Fe +2
Fe +3
What oxidation numbers might you
predict for Manganese? (Mn)
The roman numeral is a common
prediction if it is less than 8.
Mn +7
Remember +2 is the most common
oxidation number for metal ions
Mn+2
Mn +7
Each electron is harder to remove than
the one before so sometimes losing
electrons can be a gradual process.
Mn+2
Mn
+3
Mn +4
Mn +5
Mn +7
Determining Oxidation Numbers
• What is the oxidation number of nitrogen within a
compound?
• Would you predict -3?
• Could nitrogen have a positive oxidation number?
• How about +5?
• The fact is we can only guess as to what the oxidation
number of nitrogen is within a compound unless we
have some additional information.
Determining Oxidation Numbers
• The best way to determine oxidation
numbers is to use the formula of the
compound and examine the elements
within it.
Oxidation Number Rules
• The oxidation number of all Group 1 metals (+1), Group 2
metals (+2), Ag+, Zn2+, Cd2+, and Al3+ within compounds
is a set value.
• Hydrogen (H) has two possible oxidation numbers:
– +1 when bonded to a nonmetal
– -1 when bonded to a metal
• The oxidation number of fluorine (F) is always -1.
• In ionic compounds the nonmetal closest to fluorine is
negative.
• The sum of the oxidation numbers of all atoms (ions) in a
neutral compound = 0.
• The sum of the oxidation numbers of all atoms (ions) in a
polyatomic ion = charge on the polyatomic ion.
What is the oxidation number of nitrogen?
N2O
• N2O is nitrogen (I) oxide
• Commonly known as
“laughing gas”.
Example
NaCl
Example
BaH2
Example
PO3
3-
Example
FePO3
Example
Fe3(PO3)2