SCH4U - Assigning Oxidation Numbers - V

When existing by themselves, what oxidation numbers do elements have? (1)

• 0

When existing in a compound, what oxidation number does oxygen have? Following the other rule, what oxidation number does it have when existing by itself? (2)

• -2

• 0

When existing in a compound, what oxidation number does hydrogen have? Following the other rule, what oxidation number does it have when existing by itself? (2)

• +1

• 0

What does the Zero Sum rule state?

• In a NEUTRAL compound, the oxidation numbers of every element/atom within must add up to 0

What does the Ion Charge Rule state?

• In any type of ion (whether monatomic or polyatomic), the oxidation number of every element/atom within must add up to the total charge indicated.

In oxidation numbers, do we have to add the signs + and -?

• Yes

What are the oxidation numbers for Group 1 and Group 2 elements when in compound, respectively? (2)

• + 1 for Group 1 elements in compound

• + 2 for Group 2 elements in compound

How can we determine, after assigning oxidation numbers, which atoms were oxidized and which were reduced, and thus the oxidizing and reducing agents? (4)

• We look for change of oxidation numbers from one side of the reaction to the other

• The atom whose oxidation number becomes more positive, loses electrons and is thus oxidized; it is the reducing agent.

• The atom whose oxidation number becomes more negative, gains electrons and is thus reduced; it is the oxidizing agent.

• If the atom did not change oxidation number, it is not oxidized or reduced.