Chlorine is a greenish yellow gas that combines directly with almost all elements. Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin. You can detect an odor as low as 3.5 ppm and 1000 ppm could be fatal after a few deep breaths. It was used as a war gas in 1915. It is not found free in nature, but is commonly found as NaCl (solid or seawater). Table: Basic information and classifications of chlorine.• Name: Chlorine• Symbol: Cl• Atomic number: 17• Atomic weight: 35,453 (2) [see gm notes]• Standard state: gas at 298 K• CAS registry ID: 7782 -50-5• Group in the periodic table: 17• Group name: Halogen• Period in the periodic table: 3• Block in the periodic table: p block• Color: yellowish green• Classification: Non-metallic chlorine: historical information Chlorine was discovered by Carl William Scheele in 1774 in Sweden. Origin of the name: from the Greek word "cloros" meaning "pale green". Chlorine was discovered in 1774 by Carl Wilhelm Scheele. He achieved this through the reaction of the mineral pyrolusite (manganese dioxide, MnO2) with hydrochloric acid (HCl, then known as muriatic acid). Scheele thought the resulting gas contained oxygen. Sir Humphry Davy proposed and confirmed that chlorine was an element in 1810, and also gave it its name. Chlorine: Physical properties•melting points of chemical elements displayed on a miniature periodic table Melting point: 171.6 [or -101.5 °C (-150.7 °F)] K•boiling points of chemical elements displayed on a miniature periodic tableBoiling point: 239.11 [or -34.04 °C (-29.27 °F)] K•density of chemical elements displayed on a miniature periodic tableDensity of solid: 2030 kg m- 3...... middle of paper ......y67Ho68Er69Tm70Yb71Lu72Hf73Ta74W75Re76Os77Ir78Pt79Au80Hg81Tl82Pb83Bi84Po85At86Rn87Fr88Ra89Ac90Th91Pa92U93Np94Pu95Am96Cm97Bk98C f99Es100Fm101Md102No103Lr104Rf105Db106Sg107Bh108Hs109Mt110Ds111Rg112Cn113Uut114Fl115Uup116Lv117Uus118UuoWebElements ShopPrintable tableFollow WebElements on TwitterChemputerAbout Web ElementsCopyrightAcknowledgementsPrivacyWebElements Zazzle ShopWebElements Zazzle Shop UKWebElements: the periodic table on the WWW [http://webelements.com/]Copyright 1993-2012 Mark Winter [University of Sheffield and WebElements Ltd, UK]. All rights reserved.