The halogen group of elements is the most reactive of the nonmetals. It is also the most reactive group of all chemical elements. Fluorine is the most reactive element in this group.
Halogens are highly reactive because they are all electronegative. They can gain electrons very quickly which is what makes them react so strongly to other elements. Halogens can form many bonds very fast. Fluorine, for example, only has the choice of losing seven electrons or gaining one, so it almost always gains the one electron since this is much easier. As a result, it often rips electrons away from other elements in order to gain this electron and become stable.
The halogens include fluorine, chlorine, bromine, iodine and astatine. The most reactive element from group seven is fluorine which is at the top of that section of the periodic table. The further down the group you go, the less reactive the element is. Halogens are poisonous to humans on the whole, though each one is poisonous to a different degree. The halogens also tend to be poor conductors of electricity and heat. These chemicals exist at all phases of matter including solid, liquid and gas; they are the only elemental group that has this characteristic.