Oxidation: is any chemical reaction that involves the moving of electrons. Specifically, it means the substance that gives away electrons is oxidised. When iron reacts with oxygen it forms a chemical reaction called rust because it has been oxidized (the iron has lost some electrons) and the oxygen has been reduced (the oxygen has gained some electrons).
When Oxygen reacts with the exposed chemicals in the exposed surface of a material it starts breaking down through a process known as oxidation as per the above example where a metal such as iron being broken down resulting in the formation of rust. Another example of oxidation is that of an Apple where when cut the flesh of the Apple is exposed to the air which contains oxygen which reacts with the flesh of the Apple breaking it down visible as the flesh turns brown.
The driving element in this Oxidation process is Oxygen because it follows the octet rule that is it wants to have 8 electrons in its outer most shell. Because Oxygen only has 6 electrons it its outer shell it wants to gain 2 more electrons to feel complete. Therefore, it really likes combining with electron donating atoms when it gets a chance especially with Hydrogen hence water as H 2 O.
The Oxygen Hydrogen bonding is the process that allows the Human Body to change sugars into energy during respiration. But sometimes, up to 2% of the time, in this human respiration activity Oxygen comes out of the process not totally satisfied. Thus, instead of it being its normal mellow stable self it evolves into a totally agitated state completely rogue in character known as a free radical that will practically bond with anything. It will try to pair up with the fats, proteins in the red blood cells even the DNA. And when it does this the free radical changes the chemical structure of those molecules and most of the time cause cell damage.