OXIDATION AND REDUCTION
When an atom becomes involved in a bond, the atom is either oxidized or
reduced. But what do these terms mean? Well, any chemistry teacher will tell
you that an atom that loses electrons is oxidized; an atom that gains electrons is
reduced. They’ll tell you to recite “LEO says GER,” which means Lose
Electrons Oxidized and Gain Electrons Reduced. You should definitely
remember that sentence for this exam.
Losing electrons = oxidation (LEO)Gaining electrons = reduction (GER)The only kind of reaction in which an atom truly loses an electron and another
truly gains one is one that results in an ionic bond. But, as a way of keeping
track of electrons, chemists assign each term in a compound a positive or a
negative charge based upon the relative electronegativities of the atoms. For
example, take HF. H-F has a covalent bond; F has a higher electronegativity
value than does H. Although this isn’t an ionic bond, chemists will assign the H
a +1 charge and the F a −1 charge. These charges are called oxidation numbers
and are always whole numbers.
The following are some important points to remember about oxidation states:
• The atoms in any compound can be assigned oxidation states.
The charges given to the atoms are formal charges that reflect
their electronegativities.
• For any compound, the total number of electrons given up by
atoms is the same as the number gained. Thus, the oxidation
states of all of the atoms in a neutral compound always add up to
zero.