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Ebook Advanced inorganic chemistry - A comprehensive text: Part 2

(BQ) Part 2 book "Advanced inorganic chemistry - A comprehensive text" has contents: Introduction to the transition elements, the electronic structures of transition matal complexes, classical complexes, organometallic compounds in homogeneous catalytic reactions,.and other contents. | 17 The Noble Gases THE ELEMENTS 17-1. Group Trends The closed-shell electronic structures of the noble-gas atoms are completely stable as shown by the high ionization potentials especially of the lighter members Table 17-1 . The elements are all low-boiling gases whose physical properties vary fairly systematically with atomic number. The boiling point of helium is the lowest of any known substance. The boiling points and heats of vaporization increase monotonically with increasing atomic number. TABLE 17-1 Some Properties of the Noble Gases Outer shell configuration Atomic number 1st IP eV Normal b.p. K AZZvap J kJ mol-1 by volume in the atmosphere Promotion energy eV ns2np6 ns2nps n l s He Is2 2 24.58 4.18 0.09 5.24 X 10- Ne 2r22p6 10 21.56 27.13 1.8 1.82X 10-3 16.6 Ar 3s23p6 18 15.76 87.29 6.3 0.934 11.5 Kr 4s24p6 36 14.00 120.26 9.7 1.14X10-3 9.9 Xe 5s25p6 54 12.13 166.06 13.7 8.7 X 10-6 8.3 Rn 6s26p6 86 10.75 208.16 18.0 6.8 The heats of vaporization are measures of the work that must be done to overcome interatomic attractive forces. Since there are no ordinary electronpair interactions between noble-gas atoms these weak forces must be of the van der Waals or London type such forces are proportional to the polarizability and inversely proportional to the ionization potentials of the atoms they increase therefore as the size and diffuseness of the electron clouds increase. 495 496 CHEMISTRY OF NONTRANSITION ELEMENTS The ability of the noble gases to enter into chemical combination with other atoms is very limited only Kr Xe and Rn having so far been induced to do so and only bonds to F and o are stable. This ability would be expected to increase with decreasing ionization potential and decreasing energy of promotion to states with unpaired electrons. The data in Table 17-1 for ionization potentials and for the lowest-energy promotion process show that chemical activity should increase down the group. According to present knowledge the threshold of actual .