Why is Fluorine the most reactive element in group 7?
Fluorine is the most electronegative element. Because it has a lack of only one electron to fill its shell, and because that shell is relatively close to the nucleus, the attraction to an electron from another atom is strongest, and fluorine is thus most likely to react with another atom. As your atom gets larger and the shells further from the nucleus, the reactivity diminishes slightly; that explains chlorine and bromine as you go down group 7.
As you go down group 7 the reactivity of elements increases. This is because the elements need to gain an electron to form a more stable compound. Group 7 elements have 7 outer electrons and need to gain one electron. As the period no. increases ie. as you go down the group to chlorine, bromine etc. The atoms become bigger and the outer shell of electrons is further away. The attraction of these electrons (by the positive protons in the nucleus) is therefore less and they therefore don’t react as easily because the electron from the element it is reacting with doesn’t join the group 7 element as easily (weaker attraction of outer electrons). That is why fluorine is the most reactive and the ones below it on the periodic table are less reactive.
