Chlorine was discovered by Carl Wilhelm Scheele in 1774, although he mistakenly believed it to be a compound rather than an element.
He produced chlorine by reacting hydrochloric acid (HCl) with manganese dioxide (MnO₂), but thought the gas produced was a compound containing oxygen. It was not until 1810 that Sir Humphry Davy confirmed chlorine to be an element and gave it its name, derived from the Greek word ‘chloros’, meaning greenish-yellow, reflecting its distinctive color.
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- Symbol: Cl
- Atomic Number: 17
- Atomic Weight: 35.45
- Element Classification: Halogen
- Discovered By: Carl Wilhelm Scheele
- Discovery Date: 1774
- Name Origin: Greek: ‘chloros’ (greenish yellow)
- Density(g/cc): 0.003214 (at 0°C, 101.325 kPa)
- Melting Point: -101.5°C
- Boiling Point: -34.04°C
- Appearance: Greenish-yellow gas
- Atomic Radius(pm): 79
Relation to Other Elements
Chlorine is a member of the halogen group in the periodic table, characterized by their high reactivity and the tendency to form salts with metals. As with other halogens, chlorine has seven valence electrons, one short of a full octet, making it highly eager to gain an electron and form ionic or covalent bonds. Chlorine’s reactivity is significant, although it is less reactive than fluorine. It can form a wide variety of compounds, including chlorides, hypochlorites, and chlorofluorocarbons (CFCs), with various elements and molecules.
Natural Occurrence
Chlorine is not found free in nature due to its high reactivity but is abundant in the form of chloride ions (Cl⁻). These ions are a major component of salt (sodium chloride, NaCl) found dissolved in seawater and in mineral deposits as halite. Chlorine is essential for many forms of life, including humans, where it is a critical electrolyte involved in the regulation of osmotic balance and acid-base homeostasis.
Uses
Chlorine has a wide array of applications, reflecting its versatility:
- Water Treatment: Chlorine is used extensively to disinfect drinking water and swimming pools, killing bacteria and other pathogens to prevent waterborne diseases.
- Chemical Industry: It is a key reactant in the production of a wide range of chemicals, including PVC (polyvinyl chloride), solvents, and many other synthetic materials.
- Bleaching: Chlorine and its compounds, like sodium hypochlorite (bleach), are used in the paper and textile industries to bleach products.
- Cleaning Products: Chlorine-based cleaners are effective in killing bacteria and are widely used in household and industrial cleaning agents.
- Medicine: Chlorine compounds are used in antiseptics and some pharmaceuticals.
The discovery of chlorine was pivotal in the development of modern chemistry and has had profound impacts on public health, sanitation, and the chemical industry. Its widespread use in water treatment has been crucial in preventing waterborne diseases, while its applications in the chemical industry have led to the development of a wide array of products and materials.