17. Chlorine

Name: Chlorine
Symbol: Cl
Atomic Number: 17
Atomic Mass: 35.4527 amu
Melting Point: -100.98 °C (172.17 °K, -149.764 °F)
Boiling Point: -34.6 °C (238.55 °K, -30.279997 °F)
Number of Protons/Electrons: 17
Number of Neutrons: 18
Classification: Halogen
Crystal Structure: Orthorhombic
Density(293 K): 3.214 g/cm3
Color: green

Chlorine is a greenish yellow gas which combines directly with nearly all elements. Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odour, and 1000 ppm is likely to be fatal after a few deep breaths. It was used as a war gas in 1915. It is not found in a free state in nature, but is found commonly as NaCl (solid or seawater).

In nature chlorine is found only as the chloride ion. Chlorides make up much of the salt dissolved in the Earth's oceans — about 1.9% of the mass of seawater is chloride ions. Even higher concentrations of chloride are dissolved in the Dead Sea and in underground brine deposits.

Chlorine was discovered in 1774 by Carl Wilhelm Scheele, who mistakenly thought it contained oxygen. Chlorine was given its name in 1810 by Humphry Davy, who insisted that it was in fact an element.

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Non-metals H, C, N, O, P, S, Se
Halogens F, Cl, Br, I, At
Alkali metals Li, Na, K, Rb, Cs, Fr
Alkaline Earth Be, Mg, Ca, Sr, Ba, Ra
Transition metals Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Uub
Metalloids B, Si, Ge, As, Sb, Te, Po
Other metals Al, Ga, In, Sn, Tl, Pb, Bi
Rare Earth Lu, Lr, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No
Noble gases He, Ne, Ar, Kr, Xe, Rn

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