Chlorine, liquified under a pressure of 8 bar at room temperature. The liquid column size is ca. 0.3×3 cm.
At standard temperature and pressure, two chlorine atoms form the diatomic molecule Cl2. This is a yellow-green gas that has its distinctive strong smell, the smell of bleach.The bonding between the two atoms is relatively weak (only 242.580 ±0.004 kJ/mol), which makes the Cl2 molecule highly reactive. The boiling point at regular atmosphere is around −34 ˚C, but it can be liquefied at room temperature with pressures above 8 atmospheres.
[edit]Chemical characteristics
Along with fluorine, bromine, iodine, and astatine, chlorine is a member of the halogen series that forms the group 17 (formerly VII, VIIA, or VIIB) of the periodic table. Chlorine forms compounds with almost all of the elements to give compounds that are usually called chlorides. Chlorine gas reacts with most organic compounds, and will even sluggishly support the combustion of hydrocarbons.
[edit]Hydrolysis
At 25 °C and atmospheric pressure, one liter of water dissolves 3.26 g or 1.02 L of gaseous chlorine. Solutions of chlorine in water contain chlorine (Cl2), hydrochloric acid, and hypochlorous acid:
Cl2 + H2O HCl + HClO
This conversion to the right is called disproportionation, because the ingredient chlorine both increases and decreases in formal oxidation state. The solubility of chlorine in water is increased if the water contains dissolved alkali hydroxide, and in this way, chlorine bleach is produced.
Cl2 + 2 OH– → ClO– + Cl– + H2O
Chlorine gas only exists in a neutral or acidic solution.
[edit]Compounds
See also Category: Chlorine compounds.
Chlorine exists in all odd numbered oxidation states from −1 to +7, as well as the elemental state of zero and four in chlorine dioxide (see table below, and also structures in chlorite). Progressing through the states, hydrochloric acid can be oxidized using manganese dioxide, or hydrogen chloride gas oxidized catalytically by air to form elemental chlorine gas.
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