[IgorPartola]

I will attempt at conveying my simplistic understanding of it (physics major here): electrons are negative, protons are positive. Electrons want to be matched with protons. Two atoms can form a strong bond if they have just enough electrons to bond them but not enough to repel each other. Oxygen can bond to oxygen via a double covalent bond (http://www.chemguide.co.uk/atoms/bonding/doublebonds.html) but it has too many electrons, so it is essentially on the brink of breaking up (much more so, than say H2O or CO2). Basically, if you have an unstable oxygen bond, many things introduced nearby can disturb it, starting a reaction.

The rest is easy: a single atom of Oxygen is extremely reactive. If you take an O=O molecule (= means double covalent bond) and add some fuel, you get fire. At high concentrations, drop in just a bit of fuel and you can get a violent reaction.

[dnautics]

Urg, O2 is actually a very bad example, because it's actually 'O-O' (where the ticks are radicals), this is called "triplet" oxygen. In the ground state it's a single bonded O2 with two free, unpaired electrons. There is "singlet" oxygen which is typically depicted as O=O, but it's actually O triple-bond O with two antibonding electrons that negate one of the 'triple' bonds which makes it effectively O=O but very different in reality.

[CamperBob2]

If the OP asks about Newton's laws, and the parent responds with a brief summary of F=ma and friends, what good does it do to launch into a discourse about how all that stuff is totally wrong in the context of Lorentzian spacetime?

99% of physics and chemistry education consists of learning that whatever they taught you last semester wasn't quite right.