The halogens are located on the left of the noble gases on the periodic table. These five toxic, non-metallic elements make up Group 17 of the periodic table and consist of: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Although astatine is radioactive and only has short-lived isotopes, it behaves similar to iodine and is often included in the halogen group. Because the halogen elements have seven valence electrons, they only require one additional electron to form a full octet. This characteristic makes them more reactive than other non-metal groups. 8.13.1: Physical Properties of the Halogens It can be seen that there is a regular increase in many of the properties of the halogens proceeding down group 17 from fluorine to iodine. This includes their melting points, boiling points, the intensity of their color, the radius of the corresponding halide ion, and the density of the element. On the other hand, there is a regular decrease in the first ionization energy as we go down this group. As a result, there is a regular increase in the ability to form high oxidation states. 8.13.1.1: Atomic and Physical Properties of Halogens 8.13.1.2: General Properties of Halogens 8.13.1.3: Halogen Group (Group 17) Trends 8.13.1.4: Physical Properties of the Group 17 Elements 8.13.2: Chemical Properties of the Halogens Covers the halogens in Group 17: fluorine (F), chlorine (Cl), bromine (Br) and iodine (I). Includes trends in atomic and physical properties, the redox properties of the halogens and their ions, the acidity of the hydrogen halides, and the tests for the halide ions. 8.13.2.1: Halide Ions as Reducing Agents 8.13.2.2: Halogens as Oxidizing Agents 8.13.2.3: Interhalogens 8.13.2.4: More Reactions of Halogens 8.13.2.5: Oxidizing Ability of the Group 17 Elements 8.13.2.6: Testing for Halide Ions 8.13.2.7: The Acidity of the Hydrogen Halides 8.13.3: Chemistry of Fluorine (Z=9) Fluorine (F) is the first element in the Halogen group (group 17) in the periodic table. Its atomic number is 9 and its atomic weight is 19, and it's a gas at room temperature. It is the most electronegative element, given that it is the top element in the Halogen Group, and therefore is very reactive. It is a nonmetal, and is one of the few elements that can form diatomic molecules (F2). 8.13.4: Chemistry of Chlorine (Z=17) Chlorine is a halogen in group 17 and period 3. It is very reactive and is widely used for many purposes, such as as a disinfectant. Due to its high reactivity, it is commonly found in nature bonded to many different elements. 8.13.4.1: The Manufacture of Chlorine 8.13.5: Chemistry of Bromine (Z=35) Bromine is a reddish-brown fuming liquid at room temperature with a very disagreeable chlorine-like smell. In fact its name is derived from the Greek bromos or "stench". It was first isolated in pure form by Balard in 1826. It is the only non-metal that is a liquid at normal room conditions. Bromine on the skin causes painful burns that heal very slowly. It is an element to be treated with the utmost respect in the laboratory. 8.13.6: Chemistry of Iodine (Z=53) Elemental iodine is a dark grey solid with a faint metallic luster. When heated at ordinary air pressures it sublimes to a violet gas. The name iodine is taken from the Greek ioeides which means "violet colored". It was discovered in 1811 by Courtois. 8.13.7: Chemistry of Astatine (Z=85) Astatine is the last of the known halogens and was synthesized in 1940 by Corson and others at the University of California. It is radioactive and its name, from the Greek astatos, means "unstable". The element can be produced by bombarding targets made of bismuth-209 with high energy alpha particles (helium nuclei). Astatine 211 is the product and has a half-life of 7.2 hours. The most stable isotope of astatine is 210 which has a half-life of 8.1 hours. Thumbnail: Chlorine gas in an ampoule. (CC-BY-SA; W. Oelen ( http://woelen.homescience.net/science/index.html )).