Multiple choice, continued (3 points each). Name:__________________ Please circle your answer. There is only one correct answer to each question. 36. How many different resonance structures can be drawn for the molecule SO3 without having to violate the octet rule on the sulfur atom? A) 5 B) 4 C) 3 D) 2 37. The central atom in _______ does not violate the octet rule. A) CF4 B) KrF2 C) SF4 D) XeF4 38. For a given arrangement of ions, the lattice energy increases as ionic radius _________ and as ionic charge __________. A) increases, increases B) decreases, decreases C) increases, decreases D) decreases, increases 39. Of the molecules below, only ________ is nonpolar. A) HCl B) NH3 C) SO2 D) CO2 40. Using the table of bond dissociation energies, ∆H for the reaction 2HCl (g) + F2 (g) à 2HF (g) + Cl2 (g) is __________ kJ. Bond D (kJ/mol) H – Cl 431 F – F 155 H – F 567 Cl – Cl 242 A) –359 B) -223 C) 359 D) 223 41. Considering its Lewis structure, the electron-domain geometry of oxygen in OF2 is ___________. A) trigonal planar B) trigonal bipyramidal C) octahedral D) tetrahedral 42. The electron-domain geometry and the molecular geometry of ammonia, NH3, are __________ and __________, respectively. A) tetrahedral, trigonal pyramidal B) tetrahedral, trigonal planar C) bent, bent D) trigonal planar, bent

Here are the answers to your multiple-choice questions:

36. C) 3

37. A) CF4

38. D) decreases, increases

39. D) CO2

40. A) –359

41. D) tetrahedral

42. A) tetrahedral, trigonal pyramidal

Explanation of the electron-domain and molecular geometry of ammonia (NH3):

• Electron-domain geometry:

  • To determine the electron-domain geometry, you need to count the number of electron domains around the central atom (nitrogen in this case). An electron domain can be a bonding pair of electrons (single, double, or triple bond) or a lone pair of electrons.

  • In ammonia (NH3), the nitrogen atom has three bonding pairs with the three hydrogen atoms and one lone pair of electrons. So, there are a total of four electron domains.

  • According to VSEPR theory, four electron domains around a central atom arrange themselves in a tetrahedral geometry to minimize repulsion.

• Molecular geometry:

  • The molecular geometry describes the arrangement of the atoms in space, considering the positions of the atoms and not the lone pairs.

  • In ammonia (NH3), although the electron-domain geometry is tetrahedral, the molecular geometry is trigonal pyramidal. This is because the lone pair on the nitrogen atom repels the bonding pairs, pushing them closer together and resulting in a pyramid shape.

In summary, the electron-domain geometry considers all electron domains (bonding pairs and lone pairs), while the molecular geometry only considers the arrangement of atoms. For ammonia, the electron-domain geometry is tetrahedral, and the molecular geometry is trigonal pyramidal due to the presence of a lone pair on the nitrogen atom.