Symbol: Cl Atomic mass: 35.453 u Electron configuration: [Ne] 3s23p5 Atomic number: 17 Melting point: -101.5 °C Electrons per shell: 2, 8, 7
Chlorine is a chemical element with symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity, behind only oxygen and fluorine.
The most common compound of chlorine, sodium chloride (common salt), has been known since ancient times. Around 1630, chlorine gas was first synthesised in a chemical reaction, but not recognised as a fundamentally important substance. Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, and this was confirmed by Sir Humphry Davy in 1810.
Elemental chlorine is commercially produced from brine by electrolysis. The high oxidising potential of elemental chlorine led to the development of commercial bleaches and disinfectants and a reagent for many processes in the chemical industry. Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of the organic chemicals such as polyvinyl chloride, and many intermediates for the production of plastics and other end products which do not contain the element. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them clean and sanitary. Elemental chlorine at high concentrations is extremely dangerous and poisonous for all living organisms and was used in World War I as the first gaseous chemical warfare agent.
In the form of chloride ions, chlorine is necessary to all known species of life. Other types of chlorine compounds are rare in living organisms and artificially produced chlorinated organic range from inert to toxic. In the upper atmosphere, chlorine-containing organic molecules such as chlorofluorocarbons have been implicated in ozone depletion. Small quantities of elemental chlorine are generated by oxidation of chloride to hypochlorite in neutrophils as part of the immune response against bacteria.
Sodium chloride is the most common compound of chlorine, and it is abundant on Earth, especially in seawater.
Chlorine in its pure form is yellowish-green, but its common compounds are typically colourless.
Chlorine is capable of joining with practically every element, producing a chloride.
In many of these chloride forms, chlorine is vital for living organisms.
Highly concentrated pure chlorine is dangerous to live beings, though.
It also creates a wide variety of oxides.
Chlorine is a widely used oxidizing agent and is also potentially a reactive agent.
Chlorine has two stable isotopes, Cl-35 and Cl-37.
Its isotope Cl-36 is radioactive and was first found produced in seawater surrounding nuclear test fires in the atmosphere.
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