Molecular Structure and Bonding Knowledge Required: (1) The meaning of the terms ionization energy and electron affinity. (2) The characteristics of different types of chemical bonds. (3) The relationship between types of chemical bonds and values of ionization energy and electron affinity. Thinking it Through: Elements with low ionization energy readily lose electrons to form positive ions. Elements with high electron affinity readily accept electrons to form negative ions. Ionic bonds, correct choice (D), result when atoms exchange electrons. Covalent bonds, choice (A), result when atoms each contribute an electron to a shared pair. Coordinate covalent bonds, choice (C), are similar except one of the two atoms furnishes both electrons. Metallic bonds, choice (B), result when atoms free one or more valence electrons to the metal lattice. MS-7. The compound CF3CHCIF is being considered as a replacement for CBrF3 as a fire-extinguishing agent because CBrF3 has been shown to deplete stratospheric ozone. What are the most probable products if a molecule of CF3CHCIF is bombarded with high-energy photons? Bond C-C C- Cl C-F C-H CF3 + CHClF CF3CHF +Cl (B) (D) CF2CHClF + F CF3CClF + H Bond Energy, kJ·mo1-1 346 327 485 411 Knowledge Required: (1) The knowledge of the interaction of photons with covalent bonds. (2) The interpretation of bond energy data. Thinking it Through: High-energy photons, such as those in the ultraviolet part of the electromagnetic spectrum, have enough energy to disrupt covalent bonds. In choosing from the set of possible products resulting from breaking at least one covalent bond, it may be helpful to consider the Lewis structure. Choice (A) requires breaking the C-C bond, which would require 346 kJ per mol. Choice (B) requires breaking one of the C-F bonds, but that would require 485 kJ per mol. The correct choice (C) results from breaking a C-Cl bond, the bond requiring the least energy of the choices given, 327 kJ per mol. Choice (D) could result if a C-H bond were broken, but that is less favorable at 411 kJ per mol. Note: Halon compounds contain bromine covalently bonded to carbon. This bond is even more easily broken by high-energy photons. The C-Br bond energy is 285 kJ·mo1-1• MS-8.