Why is flourine so reactive

Why is flourine so reactive?In its natural diatomic form(f2), both atoms have 8 valence electrons. Should it not be stable?

You are right that diatomic fluorine satisfies the octet rule. However, it is a very weak single bond that is easily broken. At this point, it becomes electron hungry and will react with pretty much anything to get that extra electron, releasing a great deal of energy in the process. It's also why F2 is unstable; the individual atoms "want" the electrons so much that they are bad at sharing.

Fluorine has the unique postion of having 9 protons in the nucleus and 9 electrons in the neutral atom. but by accepting and extra electron to have 9 protons and a now 10 electrons and form a negativley charged ion ( -1 charge valence ) which now configures the electrons to filled energy levels similar to the noble gas Neon. So fluorine wants to gain this electron and so its reactivity is very high. The ability to want an electron and keep the electron is referred to the electron affinity and elctronegativity respectfuly of the ion which for fluorine is the highest. So fluroine is reactive.

it's outer shell only needs one more electrons to complete it, so it'll do anything

they are the drug addicts of the periodic table