Chapter 10 Oxidation Numbers Oxidation Number The oxidation

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) Al 3+ (oxidation number = +3) O 2ˉ (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+, Zn 2+, Cd 2+, and Al 3+ 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? N 2 O • N 2 O is nitrogen (I) oxide • Commonly known as “laughing gas”.

Example Na. Cl

Example Ba. H 2

Example 3 PO 3

Example Fe. PO 3

Example Fe 3(PO 3)2