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General Chemistry - Oxidation Numbers

Oxidation numbers are numbers for each atom that describe the number of electrons it loses or gains when it reacts. For a molecule the oxidation numbers from all the atoms must add up to zero to make a neutral molecule. Try to remember the following oxidation numbers; group 1A oxidation number +1, group 2A oxidation number +2, group 3A oxidation number +3, fluorine oxidation number -1, oxygen oxidation number -2, noble gases oxidation number 0. Now if you need to figure out the oxidation number of an atom in a molecule you can use these values to figure out the rest of them and find the value so they all add up to zero. 

Oxidation reduction reaction :
In an oxidation-reduction, redox, reaction the oxidation numbers change because in the newly formed compounds the atoms have to donate or accept fewer or more electrons to the bonds. Reduction is when the oxidation number decreases and the atom gains electrons. Oxidation is when the oxidation number increases and the atom loses electrons. 

Oxidizing and reducing agents :
An oxidizing agent or oxidant causes another atom to be oxidized and gets reduced in the process. A reducing agent or reductant causes another atom to be reduced and gets oxidized in the process.