Inorganic chemistry: Oxidising Strength of Halogen?

The elements fluorine, chlorine, bromine, iodine, and astatine form a group or family in the Periodic Table known as the halogens (salt formers). As a group, these elements are unique in several ways. All three states of matter are represented by halogens at room temperature and one atmosphere pressure: fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. As elements, all exist as diatomic molecules. Because of their high reactivity, halogens are not found free in nature, but are usually produced from halide salts.

When considering the halogens, particularly during laboratory activities and demonstrations, one usually concentrates on chlorine, bromine, and iodine. There is a good reason for this. All known isotopes of naturally occurring astatine are radioactive with relatively short half-lives. It is estimated that only a few milligrams of astatine exist at the earth’s surface at any particular time. Fluorine, on the other hand, has a single stable isotope and is the second most abundant of the halogens at the earth’s surface—if the hydrosphere and lithosphere are combined; chlorine is most abundant. But fluorine is the most reactive of all elements, reacting with all other elements except the noble gases helium, neon, and argon. Fluorine, which is prepared by electrolysis, cannot be used for reactions in water solution because it oxidizes water, but can be stored in stainless steel vessels because protective fluoride coatings are formed.

The most obvious chemical property of halogen elements is their ability to act as oxidizing agents. The relative oxidizing ability of halogens corresponds to their order in the Periodic Table, F2 > Cl2 > Br2 > I2 . This trend can be amply shown by a student laboratory activity and/or teacher demonstration and correlated to trends in atomic size, electron affinity, and electronegativity. Commercially,Cl2 is obtained by the electrolysis of NaCl solution; Br2 and I2 are, in turn, produced by Cl2 oxidation of Br– and I – , respectively. For example:

Cl2(g) + 2Br–(aq) ---> Br2(aq) + 2Cl–(aq)

A major use of Cl2 is in water treatment, where its action on pathogens has led to enormous improvement in the public’s general health. All halogens are extensively used in the synthesis of organic compounds where properties may be tailored by replacing hydrogen atoms with halogen atoms. Of particular note are Freons and halogen-containing polymers such as polyvinyl chloride (PVC) and fluorine-containing Teflons. Many of these halogenated hydrocarbons have been found to be highly toxic, potential carcinogens or, as in the case of Freons, environmentally unsound and so have been or are being removed from general use.

All halogens, with the exception of fluorine, exhibit oxidation states of –1, 0, +1, +3, +5, and +7 (F exhibits only –1 and 0). The most common state is the halide or –1 state; crystalline metallic halides are common compounds. The iodide ion is a reasonably good reducing agent and can cause the reduction of metallic ions such as Fe3+ to Fe2+ and Cu2+ to Cu+ . A clear distinction must be made between elemental halogens and halide ions during the study of “halogens.”

Oxoanions and oxyacids of halogens are themselves potent oxidizing agents that, in the form of “bleaches,” “cleaners,” or pool additives, find their way into consumer products. Common liquid “chlorine” bleaches are not chlorine water solutions, but rather sodium or calcium hypochlorite solutions; the hypochlorite ion does the bleaching. It should be emphasized that chlorine bleaches and ammonia-containing cleansers should never be mixed, since they react to form very toxic chloramine (NH 2 Cl).

The importance of halogens to human history is detailed later, as are links between halogen chemistry and issues of importance to our everyday lives.

This means which is the best oxidizing agent, which means itself becomes reduced and gains electrons.

Cl is the most electronegative so it would be the strongest.

Br- would be a lousy oxizing agent because it cant easily gain an electron because it would be Br-2.

So this is your increasing order of oxidising strenghths

Br-, Br2, Cl2

inorganic chemistry oxidising strength halogen

Best Oxidizing Agents