Transcript oxidation number

Chapter 10
Oxidation Numbers
With
Manganese Ions Demo
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)
The periodic table can help 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 an oxidation number of zero, and
fluoride (F-) which is always a 1-, all other
nonmetals could have positive oxidation
numbers as well as the possibility of being
negative.
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.
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
we predict for Vanadium?
V = [Ar]4s23d3
V2+ = [Ar]3d3
V5+ = [Ar]
• This gives the range of possible
oxidation numbers for Vandadium
(V2+ through V5+)
What oxidation numbers might you
predict for Manganese? (Mn)
Mn+2
The most common oxidation
number for metal ions 2+
Mn+2
The most common oxidation
number for metal ions 2+
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 +6
Mn +7
Electrons do not have to be lost one at a
time. The process can be rather random.
Mn
Mn
+2
Mn +4
Mn +6
Mn +7
Demonstration
a
Mn
Demonstration
a
Mn
Determining Oxidation Numbers
• What is the oxidation number of nitrogen
([He]2s22p3) within a compound?
• Would you predict -3?
• Could nitrogen have a positive oxidation number?
• How about +3 or maybe +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
number of an element is to examine the
formula of the compound that the element
is in.
• We then use some basic rules to help us
make a determination as to the oxidation
numbers of the elements that make up
the 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 a compound the nonmetal closest to fluorine is
negative. (Oxygen is the next element most likely to be
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
Homework
• Worksheet Names and Formulas of Ions
(Due tomorrow).
• Ions and Oxidation Numbers Worksheet
(Due in two days).