Oxidation Numbers

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Chapter 10

• Oxidation Numbers

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Oxidation Number

• The oxidation number is the charge on a single
  atom.

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Oxidation Number

• The oxidation number is the charge on a single
  atom.
• Examples
• Na (oxidation number 1)
• Cl (oxidation number -1)
• Al3 (oxidation number 3)
• O2 (oxidation number -2)

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We can use the periodic table to determine
oxidation numbers.
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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.

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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.

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• 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

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What common ions can Iron form? Often the
electron configuration can help us to understand
why certain oxidation numbers form.
Fe 3
Fe 2
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Most transition metal elements have more than one
positive ion. (However 2 is the most common
oxidation number for metal ions).
Fe 3
Fe 2
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What oxidation numbers might you predict for
Manganese? (Mn)
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The roman numeral is a common prediction if it is
less than 8.
Mn 7
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Remember 2 is the most common oxidation number
for metal ions
Mn2
Mn 7
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Each electron is harder to remove than the one
before so sometimes losing electrons can be a
gradual process.
Mn 4
Mn 5
Mn 3
Mn2
Mn 7
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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.

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Determining Oxidation Numbers

• The best way to determine oxidation numbers is to
  use the formula of the compound and examine the
  elements within it.

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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.

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What is the oxidation number of nitrogen?

• N2O

• N2O is nitrogen (I) oxide
• Commonly known as laughing gas.

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Example

• NaCl

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Example

• BaH2

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Example

• PO33-

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Example

• FePO3

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Example

• Fe3(PO3)2