Halogens: Group trend in properties e.g. volatility and reactivity.

Melting points and boiling points increase as you go down the group.
Fluorine and chlorine are gases at room temperature, bromine is a liquid and iodine and astatine are solids. There is a trend in physical state from gas to liquid to solid as you go down the group.
The color of the halogens get darker as you go down the group. Fluorine is very pale yellow, chlorine is yellow-green, and bromine is red-brown. Iodine crystals are shiny purple, but easily turn into a dark purple vapour when are warmed up
Volatility and reactivity of the halogens decrease as you go down the group.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/periodic_table/group7rev1.shtml