Cl,Br,I:-1,0,+1,+3,+5,+7 3)Comparing with other families, halogens are most active non-metals, and they have highe electronegative and first ionization energy Element CI Br Atomic number 17 35 53 Atomic radius/pm 64 114133 I,/kJ.mor" 1681125111401008 EA/kJmo1|-3279|-349-3247-2951 40302825 Section Two Elementary Substance of halogens 1. Physical properties 1)The elements all form diatomic molecules, and when they exist in the solid state, they are molecular crystals 2)They have low melting and boiling points, but the melting and boiling points of the elements increase with increased atomic number. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid 3)The halogen molecules are all colored. This is due to the absorption of visible light. The excitation energies follow the same trend as the ionization energies; excitation of the larger iodine atom requires less energy. Gaseous molecules of F2 absorb violet light(high energy)and therefore appear yellow, whereas gaseous molecules of I2 absorb yellow light(lower energy)and appear CI Br2 State Liquid Solid Color Pale yellow Olivine Red-brown Purple-black Color Light be absorbed 第22页 2006-0第 22 页 2006-02-22 22 2) Oxidation number: F: 0, -1 Cl, Br, I: -1, 0, +1, +3, +5, +7 3) Comparing with other families, halogens are most active non-metals, and they have highest electronegative and first ionization energy Element F Cl Br I Atomic number 9 17 35 53 Atomic radius/pm 64 99 114 133 I1/kJ•mol-1 1681 1251 1140 1008 EA1/kJ•mol-1 -327.9 -349 -324.7 -295.1 χp 4.0 3.0 2.8 2.5 Section Two Elementary Substance of Halogens 1. Physical properties 1) The elements all form diatomic molecules, and when they exist in the solid state, they are molecular crystals 2) They have low melting and boiling points, but the melting and boiling points of the elements increase with increased atomic number. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid 3) The halogen molecules are all colored. This is due to the absorption of visible light. The excitation energies follow the same trend as the ionization energies; excitation of the larger iodine atom requires less energy. Gaseous molecules of F2 absorb violet light (high energy) and therefore appear yellow, whereas gaseous molecules of I2 absorb yellow light (lower energy) and appear violet Substance F2 Cl2 Br2 I2 State Gas Gas Liquid Solid Color Pale yellow Olivine Red-brown Purple-black Color Light be absorbed