Halogens: Elements of the Seventh Main Group

The halogens are one of the most chemically reactive groups of elements. They have been known for a long time, are used in many applications, and show interesting chemistry, especially in their compounds with other non-metals. Fluorine and chlorine are gases at room temperature, bromine is, alongside mercury, the only element that is liquid under standard conditions, whereas iodine, astatine, and possibly also tenness are solids under these conditions. Prepare to be surprised: halogens are much more than just table salt and iodoform.