Fall 2013 Exam III 1. c 9. e 16. (next slides) 2. b 10. a 17. (next slides) 3. a 11. e 4. d 12. b 5. b 13. c 6. c 14. d 7. c 15. e 8. d  

16. 16. a) Ionic bonding occurs between two atoms in which the electronegativity difference is so large that at least one electron is donated from one atom to the other so that an electrostatic attraction between the two atoms occurs. This is typically between a metal and nonmetal like NaCl. Covalent bonding occurs when the atoms share electrons (equally or unequally). An example is H2. 16. b) Polarity is the unequal distribution of electrons, thus ionic bonding is more “polar” in nature because the electronegativity difference is so large that an actual electron is transferred. 16. c) Ionic bonding contains ion-ion interactions which are stronger than what results from covalent bonding (dipole-dipole or London dispersion forces). Because the intermolecular forces are stronger, ionic bonding generally results in higher boiling points.

17. 17. a) 17. b) Hydrogen and oxygen are both nonpolar molecules and thus only exhibit London dispersion interactions. Water is polar and exhibits hydrogen-bonding interactions in addition to LDF and are thus stronger. Thus, it takes more energy (and a higher temperature) to break the interactions in the liquid water molecules than in hydrogen and oxygen.

17. 17. c) Water is lower in energy for this reaction. It takes more energy to break the bonds in water than it does to break the bonds in hydrogen and oxygen. A lot more energy is given off when the water is formed (in the form of a loud noise!) than what was required to break the initial hydrogen and oxygen bonds. This is an exothermic reaction and thus the products (which is water) is more stable than the reactants (hydrogen and oxygen) and is thus lower in energy. 17. d) False. Even though an endothermic component was needed (to overcome the activation energy), a lot more energy was given off than what was required to get the reaction started. (See diagram above.)