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
“predict” oxidation numbers
We can use the periodic table to
“predict” oxidation numbers
• If you have the name of the ion as you did
on the quiz that you just took. You should
know the oxidation number of the ion and
not have to make a prediction.
We can use the periodic table to
“predict” oxidation numbers
• Metals tend to form positive ions.
• Positive ions other than groups 1 & 2, Ag,
Cd, Zn, and Al can be predicted.
• Nonmetals tend to form negative ions.
• However other than fluoride (F-) which is
always -1, all other nonmetals could have
positive oxidation numbers as well.
Metals: Use the Roman numeral above each group up to 7+. If no
Roman numeral or if Roman numeral is too high use 2+.
Nonmetals: Count over from the closest Noble Gas (which has an
oxidation number of zero) assigning a negative oxidation number.
• The periodic table can often be used to
make a quick prediction as to possible
oxidation numbers of cations
Remember that these oxidation
numbers are only predictions. Most
oxidation numbers can vary.
• We predict nitrogen to have an oxidation number of -3.
• N can have positive oxidation numbers such as +5.
• However other positive oxidation numbers are
possible as in nitrogen (I) oxide (laughing gas) N2O.
Here nitrogen has an oxidation number of +1.
What common ions can Iron form?
Fe +2
Fe +3
A good number of transition metal elements possess an
ability to have more than one positive ion. (Remember +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
• The best way to determine oxidation
numbers is to have the examine the
elements within a compound.
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.
Example
NaCl
Example
BaH2
Example
PO3
3-
Example
FePO3
Example
Fe3(PO3)2
Homework
Ions and Oxidation Numbers Worksheet