Atomic Radius
Each halogen has 7 electrons in their outer shells, going down the group.
Melting and boiling points
As you go down the group, the halogens’ melting and boiling points increase. 
Reactivity
The reactivity of halogens decreases down the group, the more protons the less reactive it is, and so that means that astatine and Iodine would boil or melt faster than chlorine and fluorine; bromine is between the 4 of them. Halogens are highly reactive with alkali metals, and alkaline earths.
Uses
Chlorine plays a big part in the human body and covering 0.15% of the human body.
Fluorine, as a liquid is used as rocket fuel.
Bromine and Iodineare used to kill germs in water, and water companies use them mostly to make sure their water is fresh, clean and safe to drink.
Astatine is used to kill cancer cells.
Location on the periodic table
Periodic table elements each have been put in their groups, and not that they all share common forms, but they all have 7 electrons in their outer shell and have been divided in that form.
Abundance on earth
Halogens are found in the environment only in the form of compounds and need to be separated to have their original form.
