Apologia Chemistry: Module 16 "Reduction/Oxidation Reactions" Notes
Module 16 Notes
Reduction/Oxidation Reactions
• Oxidation number: The charge that an atom in a molecule would develop if the most electronegative atoms in the molecule took the shared electrons from the less electronegative atoms.
• Oxidation numbers are not real; they are only based on assumptions. They are useful bookkeeping tools though, and can help us keep track of electrons during a reaction.
• The sum of all oxidation numbers in a molecule must equal the charge of that molecule.
• Rules 1-4 about oxidation numbers: what’s nice about these rules is that these rules are always true.
1. When a substance has only one type of atom in it (F2, O3, Ca 2+ , or Mg for example) the oxidation number for that atom is equal to the charge of the substance divided by the number of atoms present.
2. Group 1A metals (Li, Na, K, Rb, Cs, and Fr) always have oxidation numbers of +1 in molecules that contain more than one type of atom.
3. Group 2A metals (Be, Mg, Ca, Sr, Ba, and Ra) always have oxidation numbers of+2 in molecules that contain more than one type of atom.
4. Fluorine always has a -1 oxidation number in molecules that contain more than one type of atom.
• Rules 5 and 6 about oxidation numbers: in general, these rules usually apply, though there are a few exceptions.
5. When grouped with just one other atom that happens to be a metal, H has an oxidation number of -1. In all other cases in which it is grouped with other atoms, H has an oxidation number of +1.
6. Oxygen has an oxidation number of -2 in molecules that contain more than one type of atom.
• In fact, there are exceptions to both rule #5 and rule #6. However, you will be happy to know that for this course, we will ignore those exceptions. Thus, as far as you are concerned, rules 1-6 always are true. After that, though, things get really fuzzy. If you are really stuck and none of these rules apply, you can follow this general (and often not true) guideline:
7. If all else fails, assume that
Reduction/Oxidation Reactions
• Oxidation number: The charge that an atom in a molecule would develop if the most electronegative atoms in the molecule took the shared electrons from the less electronegative atoms.
• Oxidation numbers are not real; they are only based on assumptions. They are useful bookkeeping tools though, and can help us keep track of electrons during a reaction.
• The sum of all oxidation numbers in a molecule must equal the charge of that molecule.
• Rules 1-4 about oxidation numbers: what’s nice about these rules is that these rules are always true.
1. When a substance has only one type of atom in it (F2, O3, Ca 2+ , or Mg for example) the oxidation number for that atom is equal to the charge of the substance divided by the number of atoms present.
2. Group 1A metals (Li, Na, K, Rb, Cs, and Fr) always have oxidation numbers of +1 in molecules that contain more than one type of atom.
3. Group 2A metals (Be, Mg, Ca, Sr, Ba, and Ra) always have oxidation numbers of+2 in molecules that contain more than one type of atom.
4. Fluorine always has a -1 oxidation number in molecules that contain more than one type of atom.
• Rules 5 and 6 about oxidation numbers: in general, these rules usually apply, though there are a few exceptions.
5. When grouped with just one other atom that happens to be a metal, H has an oxidation number of -1. In all other cases in which it is grouped with other atoms, H has an oxidation number of +1.
6. Oxygen has an oxidation number of -2 in molecules that contain more than one type of atom.
• In fact, there are exceptions to both rule #5 and rule #6. However, you will be happy to know that for this course, we will ignore those exceptions. Thus, as far as you are concerned, rules 1-6 always are true. After that, though, things get really fuzzy. If you are really stuck and none of these rules apply, you can follow this general (and often not true) guideline:
7. If all else fails, assume that