Why are O2 bond broken by a hydrogen to form OH?

Answer 1

• The hydrogen is attached directly to one of the most electronegative elements, causing the hydrogen to acquire a significant amount of positive charge.

• Each of the elements to which the hydrogen is attached is not only significantly negative, but also has at least one "active" lone pair.

  Lone pairs at the 2-level have the electrons contained in a relatively small volume of space which therefore has a high density of negative charge. Lone pairs at higher levels are more diffuse and not so attractive to positive things.

• and just for fun, here is another (equivalent) explanation: The normal result of O2 combining with H2 is water, H2O, not OH (although water can also be described as a combination of OH and H) but in any event, oxygen combines with hydrogen because oxygen has a stronger attraction for electrons (which is to say, a higher electronegativity) than hydrogen does, so if hydrogen and oxygen share electrons, with the electrons being unequally shared, spending more time with the oxygen than with the hydrogen, there is a net energy advantage (technically a heat of formation) which is greater than the energy of the oxygen and hydrogen by themselves.

Answer 2

The O-O bond in O2 is broken when a hydrogen atom forms a bond with one of the oxygen atoms to create an OH radical. This process is driven by the high reactivity of hydrogen, making it capable of breaking the relatively weak O-O bond in O2. The resulting OH radical is more stable than the original O2 molecule due to the formation of a new, more stable bond.