CHLORINE At room temperature, chlorine is a pale yellow-green gas. It is denser than air and will settle to the bottom of a flask.

Atomic Number: 17
Mass Number: 35.4527
Electron Configuration: 1s²2s²2p⁶3s²3p⁵
Melting Point: -101^oC
First Ionization Energy: 1251 kJ/mol
Electronegativity: 3.2
Atomic Radius: 99 pm
Ionic Radius: 181 pm

Chlorine is the second heaviest member of the halogen family. Chlorine is a very reactive and does not appear in nature in elemental form. It is, however, very widely distibuted in various compounds as the chloride ion. In elemental form it occurs as diatomic molecules and under conditions of standard temperature and pressure it exists as a pale, yellow-green gas.

The chemistry of chlorine is a consequence of the fact that chlorine is one electron short of having a noble gas electron configuration. Chlorine will react directly with many metals to form the corresponding metal halides. A mixture of hydrogen and chlorine gases will react explosively when exposed to light. Chlorides of the alkali metals and alkaline earth metals are true ionic compounds in which the chlorine exists as the chloride ion. They are generaly white crystalline solids, have high melting points, and are generally very water soluble. Chlorine also has an extensive nonmetal chemistry. Chlorine is found in many organic compounds such as dichloromethane, trichloromethane, and carbontetrachloride. Huge quantities of chlorine are used in the production of polyvinylchloride (PVC). Polyvinly chloride is used to make many objects, including plumbing pipe.

In the laboratory chlorine can be prepared by the oxidation of hydrochloric acid with an oxidixing agent such as potassium permanganate. The permanganate ion is reduced, and the chloride ion is oxidized to molecular chlorine. Industrially, chlorine is produced as a by-product in the production of sodium metal by the electrolysis of molten sodium chloride.

Chlorine combines with oxygen to form several oxoanions, or anions in which the chlorine is covalently bonded to one or more oxygen atoms. While chlorine is an electronegative element, oxygen is more electronegative, and in each compound the chlorine can be viewed as having a positive formal charge. A positive charge on an electronegative element is an unstable situation, and the chlorine oxoanions are good oxidizing agents. Reactivity increases with increasing number of oxygen atoms.

The Hypochlorite Ion. Nearly everyone has used solutions containing the hypochlorite ion whether they realize it or not; household beach is a solution of sodium hypochlorite. Calcium hypochlorite is used as a source of chlorine in swimming pools. The hypochlorite ion is normally produced in small quantities when chlorine is dissolved in water. However, this reaction does not proceed to an appreciable extent. The hypochlorite ion is aslso produced when chlorine gas dissolves in a solution of sodium hydroxde.Industrially, the hypochlorite ion is produced by electrolysis of a cold sodium chloride solutions. In this reaction, chlorine gas is produced at the anode and hydroxide ion at the cathode. The solution is vigorously stirred so that the chlorine gas and hydroxide ions mix, producing hypochlorite ions.

The Chlorate Ion. Industrially, the chlorate ion is prepared from the electrolysis of hot sodium chloride solutions. As is the case with the electrolysis of cold sodium chloride solutions, chlorine gas is produced at the anode and the hyroxide ion is produced at the cathode. However, in a hot solution the chlorine gas and hydroxide react to produce chloride and chlorate ions. Chlorate compounds are generally much less soluble than chloride ions and generall precipitate from the solution. The chlorate ion is a powerful oxiding reagent. In a reaction referred to as "instant fire" potassium chloride udnergo a spectacular reaction. Compounds containing the chlorate such as potassium chlorate ion readily decomposes to yield oxygen has when heated, and this reaction serves as a convenient method of producing oxygen has in the laboratory. Chlorate compounds are often used in fireworks.

The Perchlorate Ion. In the perchlorate ion, chlorine has a formal charge of +7, and perchlorates tend to be very unstable. Perchlorates may react explosively when the come into contact with organic matter.