Why are halogens reactive?

Halogens are reactive because:

They have high electronegativity and also high nuclear charge. So, they are reactive and also gain an electron when they react with other elements.

Since they are very reactive, halogens are very harmful to living organisms. Some of the halogens are fluorine, chlorine, bromine, iodine, astatine. These are mostly non metals. Fluorine is one of the most reactive gas and also very toxic gas. When Fluorine reacts with glass along with small amounts of water, it forms silicon tetra fluoride (SiF4). Hence fluorine should be handled with substances like the inert organofluorine compound Teflon.

try answer.com that works for me

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.