Chemistry : Group 17
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style (formerly: VII, VIIA) of the periodic table, comprising fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The artificially created element 117, provisionally referred to by the systematic name ununseptium, may also be a halogen.
*Chlorine (Cl2) was the first halogen to be discovered in 1774, followed by iodine (I2), bromine (Br2), fluorine (F2), and astatine (At), which was discovered last in 1940. The name "halogen" is derived from the Greek roots hal- (which means "salt") and -gen (which means "to form"). Together these words combine to mean "salt former", which is in reference to the fact that halogens form salts when they react with metals. Lastly, the halogens are also relevant to real-life, whether it be the fluoride that goes in toothpaste, the chlorine that disinfects drinking water, or the iodine that is responsible for the production of thyroid hormones in one's body.
The group of halogens is the only periodic table group which contains elements in all three familiar states of matter at standard temperature and pressure.
Halogens are highly reactive, and as such can be harmful or lethal to biological organisms in sufficient quantities. This high reactivity is due to the atoms being highly electronegative due to their high effective nuclear charge. They can gain an electron by reacting with atoms of other elements. Fluorine is one of the most reactive elements in existence, attacking otherwise inert materials such as glass, and forming compounds with the heavier noble gases. It is a corrosive and highly toxic gas. The reactivity of fluorine is such that if used or stored in laboratory glassware, it can react with glass in the presence of small amounts of water to form silicon tetrafluoride (SiF4). Thus fluorine must be handled with substances such as Teflon (which is itself an organofluorine compound), extremely...