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 2 ˉ (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 +3 Fe +2

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

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 +3 Mn +2 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? N2ON2O N 2 O is nitrogen (I) oxide Commonly known as “laughing gas”.

Example NaCl

Example BaH 2

Example PO 3 3-

Example FePO 3

Example Fe 3 (PO 3 ) 2