Notes and comments about
16.1 The Nature of Oxidation-Reduction Reactions
- Oxidation: refer to any chemical reaction in which an element or compound loses
electrons to another substance.
-Oxidation occurs when an atom or ion loses one or more electrons and attains a more
positive oxidation number.
- A common oxidation reaction occurs when iron metal loses electrons
to oxygen. Iron is oxidized to Fe2+, which is then again oxidized to Fe3+.
-Reduction reaction is one in which an element gains one or more electrons
-Reduction takes place when an atom or ion gains electrons and attains a more
negative oxidation number.
-
Oxidation and reduction reactions always occur together in a net process called a
redox reaction.
- An oxidizing agent is the substance that gains electrons and is reduced during a
redox reaction.
-A reducing agent is the substance that loses electrons and is oxidized during a redox
reaction.
Guidelines for Assigning Oxidation Numbers
1- The oxidation state of elements in their standard states is zero.
Example: Na, Be, K, Pb, H2, O2, P4 = 0
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Oxidation state for monatomic ions are the same as their charge.
Example: Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -2
Oxygen is assigned an oxidation state of -2 in its covalent compounds except as a
peroxide.
The oxidation number of hydrogen is +1 except when it is bonded to metals in binary
compounds. In these cases, its oxidation number is –1.
Group IA metals are +1, IIA metals are +2 and fluorine is always –1.
The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the
charge on the molecule or ion
Q: Assign the oxidation states to each element in the following.K2SO4, NO3-, H2SO4 , Fe2O3 ,
Fe3O4