Fine iodine 

 The iodine was purple crystal density of 4.93 g / cm 3. Relative atomic mass 126.9. Melting point 113.5 ° C, the boiling point of 184.35 ° C. Valence -1, +1, +3, +5 and +7. The ionization energy of 10.451 eV. With metallic luster, brittle, easily sublimated. 

 Toxic and corrosive. Soluble in ethanol, chloroform and other organic solvents, soluble in hydrogen iodate and potassium iodide solution and dark brown. Can be combined directly with most elements, but not as severe reactions like other halogens, iodine typical organic reactions 

 : Pro-electronic replacement of the aromatic compounds, the formation of the aryl iodide; iodination of the neighboring carbonyl functional groups of carbon atoms; iodine (I) in the addition reaction of multiple bonds across unsaturated hydrocarbons. But insoluble in water, as a result of the disproportionation reaction from 

 Of brown-yellow solution was acidic. In aqueous solution, the need for a strong reducing agent to make the iodine reduction (to I-). Iodine case of starch becomes blue