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Clicker Question Consider a compound formed from a Group 2 element (such as Be or Mg and designated as M below) and a Group 6 element (such as O or S and designated as X below). Which of the following is the most reasonable statement? a) The compound between M and X will be in a 1:1 ratio but it is best to think of the bond as polar covalent since atoms do not “want” to lose electrons (thermodynamically speaking). b) The bond between M and X is polar covalent as explained in “a” above, but we cannot determine the molecular formula without a molar mass. c) An ionic compound with the ions M2+ and X2- is the only stable form of the compound. d) An ionic compound with the ions M+ and X- could be thermodynamically favorable, but an ionic compound with the ions M2+ and X2- is more thermodynamically favorable. e) An ionic compound will form but we cannot predict the charges with any degree of accuracy.

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Chapter 13

Chapter 13 (OWL) 2Li(s) + 2HCl(g) → 2LiCl(s) + H2(g) 135. Given the following information: Heat of sublimation of Li(s) = 166 kJ/mol Bond energy of HCl = 427 kJ/mol Ionization energy of Li(g) = 520. kJ/mol Electron affinity of Cl(g) = –349 kJ/mol Lattice energy of LiCl(s) = –829  kJ/mol Bond energy of H2 = 432 kJ/mol Calculate the net change in energy for the following reaction: 2Li(s) + 2HCl(g) → 2LiCl(s) + H2(g)

Chapter 13

H2(g) + Cl2(g)  2HCl(g) Determine ΔHf° for HCl(g): Use Appendix 4 Predict using bond energies

Lewis Structures Determine the total number of valence electrons in the molecule. Form at least one bond between atoms in the molecule (a pair of electrons is a bond) Arrange the rest of the electrons (in pairs) to satisfy the octet rule or duet rule (for hydrogen). Watch for exceptions.

Clicker Question Which of the following has a Lewis structure most like that of the carbonate ion? a) the nitrate ion b) the sulfate ion c) carbon dioxide d) ozone (O3) e) nitrogen dioxide