The 7th Main Group - Halogens

The five elements of the VII main group are called halogens. Fluorine, chlorine, bromine, iodine and astatine belong to this group.

Chlorine is the most common halogen, followed by fluorine, which comes in second place. Bromine and iodine are significantly less frequent, and astatine is only formed as an intermediate product of radioactive fission processes. The portion of halogens in the earth’s crust is below one percent. Despite this small portion, halogens are generally widely spread in nature, except for astatine.

Because of their high reactivity, halogens only occur in compounds, though. The oceans of the seven seas contain huge quantities of dissolved salts. The halogens fluorine, chlorine and iodine are essential in traces for living organisms.

Halogens are non-metals. The first two (fluorine and chlorine) are molecular gasses under normal circumstances. Bromine is liquid and iodine and astatine are solids. With increasing atomic number, they show more and more metallic properties. Iodine, for example, conducts electricity already.

The outer shell of the halogens is composed of seven valence electrons, so they only lack a single electron for the noble gas configuration. That explains their high reactivity. Fluorine is the most reactive element of all. Within the group, the reactivity decreases with increasing atomic weight.

The most important halogens are toxic! Chlorine, for example, has a highly corrosive effect on the respiratory organs of humans. If inhaled for a period of time, it will be fatal. Since chorine also kills microorganisms very effectively, it is used to disinfect potable water.