[i_have_no_idea (OP)]

hey wats up i havent been on this site in like a over a year.  w/e, i have a question.  okay, i know it has to do with an unfilled outer level, valence, in the electron configuration but what makes elements more reactive then others? does it have to do with electronegativity? flurine is supposidly the most reactive elemnt, it has 7 valence elctrons, why isnt bromine as reactive, their in the same group?


i have a chem test very soon []

[profnick]

The energy of the Highest Occupied Molecular Orbital, (HOMO) determines how easy it is for an element or molecule to lose an electron in a reaction, and the energy of the Lowest Unoccupied Molecular Orbital, (LUMO) determines how easy it is for the element/compound to receive an electron in a reaction. The difference between the energy of these so called frontier orbitals determines reactivity.

[eric l]

If an element has to accept an electron in its outer orbital, the lighter element has an advantage (because it is also smaller) :  the attraction by the positively charged nucleus is greater.  That is why fluorine is more reactive than chlorine, which in turn is more reactive than bromine, and so on. 
If the element has to release an electron, then the heavier (and larger) element has an advantage (the attraction between electron and nucleus being lower).  That's why potassium is less reactive than sodium (and so on).
Things are of course more complicated when you have to compare elements from different groups, or when there is the possibility to accept or release different numbers of electrons.