Chlorine Periodic Table Facts
Chlorine (Cl), molecular formula Cl2 is a toxic, corrosive, greenish yellow gas of Group 17 (Group VIIA) of the periodic table chemical element uses widely as a bleaching agent in paper, pump, and textile industries. The second lightest member of the halogen family, chlorine found mostly in seawater as alkali and alkaline metal chloride and uses in the very early day of our civilization. Chlorine appears between fluorine and bromine in the periodic table and its physical and chemical properties are mostly intermediate between them. Natural chlorine consists of two common isotopes like 35Cl (76 percent) and 37Cl (24.5 percent).
The non-metallic chemical element, chlorine has chemical symbol Cl, atomic number 17, atomic weight 35.446, 35.457, melting point -101.5 °C, boiling point -34.04 °C, density 32.2 gm/liter in STP, electron configuration 1s2 2s2 2p6 3s2 3p5. Due to the presence of seven valence electrons and vacant d-orbital, chlorine exhibits oxidation number or state -1, +1, +3, +5, +6, +7. It is a highly reactive oxidizing agent with the highest electron affinity, the third-highest electronegativity after fluorine and oxygen, and very high ionization energy.
History and Abundance
Scientific research and uses of different rock salt (common salt or sodium chloride) in our environment are associated with the very early history of our incident civilization. Around 1630, chlorine gas was first developed in the chemical process but was not recognized as a chemical element. The Swedish chemist Carl Wilhelm Scheele in 1774 discovered a greenish-yellow gas by reaction of magnesium with hydrochloric acid but he fails to recognize the gas as element chlorine. In 1810, English chemist Humphry Davy establishes chlorine as an element and also suggested the name come from the Greek latter chloros, meaning yellowish green. The term halogen was given by J.S.C. Sch weigger from chlorine for its ability to form salts with the metal atoms.
Chlorine occurs mainly as crystalline solid sodium chloride (NaCl) deposited by evaporation of lakes or seawater. The concentration of sodium chloride in seawater about 2 percent. In different types of landlocked seas like the Caspian Sea and the Dead Sea, the concentration of salt increases up to 30 percent. It was also found in brine wells and rock salt deposits. The small amount of chlorine present in the blood and milk of living organisms.
Chlorine may be readily prepared in the laboratory by oxidation of hydrochloric acid by manganese dioxide (MnO2) or potassium permanganate (KMnO4). In the industry or technical scale, the elemental chlorine gas is obtained by electrolysis of sodium chloride, either molten or in aqueous solution (brine), metallic sodium, hydrogen gas, and sodium hydroxide being the by-product which is most valuable materials. In the process, we using mercury cathode, the metal being gradually discharged owing to alarming mercury pollution through the water and energy efficient process. Due to the possibility, we use traditional diaphragms (separated the electrode) by the membrane.
The old Deacon process of oxidation of hydrogen chloride by air in presence of CuCl2 chemical catalyst at 450 °C are also triad again for industrial production of chlorine gas. The chemical equilibrium may be shifted to the right by converting the Cl2 to dichloroethane uses for the production of vinyl chloride.
Uses of Chlorine
About 25 million tonnes of chlorine gas are produced annually in the world by most of the industrially developed countries. Chlorine is mainly used as a bleaching product in the paper, pulp, and textile industries, as a disinfectant in water supply and in sewage water pollution, manufacturing of hydrochloric acid, and other inorganic compounds like NaClO3, NaOCl, Al2Cl6, SOCl2. etc. Due to high oxidizing potential, elemental chlorine uses in commercial bleaches, disinfectants, and many chemical processes in the chemical industry. About 70 percent of elemental chlorine used for the production of chlorinated organic compounds like ethyl dichloride and polyvinyl chloride (PVC), and many intermediate for the production of plastic. A high concentration elemental chorine molecule is a toxic poisonous gas for living organisms and uses in World War I as a poisonous gas weapon.
Chemistry and Compounds of Chlorine
The chemical properties and reactivity of chlorine are intermediate between halogen elements fluorine and bromine. Due to the small size, low electric polarization, and absence of vacant d-orbitals for chemical bonding, the bond energies trend does not decrease from fluorine to iodine. The gradual decrease in bond energy from Cl2 to I2 exhibit poorer overlap with increasing overlapping orbitals. The fact of chlorine chemistry different from fluorine, it shows positive oxidation states. Chlorine is dissolved in many organic hydrocarbons but sparingly soluble in water, during which they disproportionate into HCl or HOCl. The solid hydrate like Cl2, 8H2O actually contains the molecule trapped in the hydrogen bonding network.
In learning chemistry, almost all the elements in the periodic table except helium, neon, and argon, chlorine form a wide range of halides. The compounds are formed by simple ionic or covalent bonding or molecular species or polymeric species. In addition to such binary halides, chlorine forms many oxohalides, hydroxohalides, and complex halides formed by several elements. AlCl3, TiCl4, PCl3, SbCl3, FeCl3, PbCl4, etc are the examples of such halides.
Hydrogen chloride or hydrochloric acid is an important compound of chlorine known to the chemist from the earliest time and uses largely in the chemical industry. HCl is conventionally prepared by the reaction of sodium chloride with concentrated sulfuric acid or burning hydrogen in Cl2 gas. The aqueous solution of the HCl molecule conducts electricity owing to extensive ionization. The weaker bond dissociation energy makes the hydrogen chloride, a strong acid in an aqueous solution (approximately pKa values = 7).
Oxides of Chlorine
The oxides of halogens are unstable compounds, the higher oxides are beings rather stable than the lower one. The stability of oxides of iodine greater than chlorine while the oxides of bromine are least stable. Cl2O, Cl2O3, ClO2, Cl2O4, Cl2O6, and ClO7 are the example of oxides formed by different types of the chemical process. In learning chemistry, chlorine forms different types of oxoacids in oxidation states +1, +3, +5, and +7 and most of them are soluble only in the aqueous solution or as salts.