CHAPTER 1 HW SOLUTIONS: STRUCTURE

Transcription

1 APTER 1 W SLUTIS: STRUTURE FRMAL ARGE 1. Indicate the formal charge on any atom that has a non-zero formal charge. a. b. c. d. e. 6-7 = = = = +1 f. g. h. i. j. 6-5 = +1 P 5-5 = = 0 (see 1e and 1g) LEWIS STRUTURES 2. Draw the Lewis structure for each formula, including lone pairs and formal charge. If a condensed formula is given, the atoms are in the implied order. The general connectivity of atoms is shown in problem g. a. 2 5 l 20 valence e b. 10 valence e c valence e l + d valence e e valence e f. 12 valence e g valence e Page 1

2 RESAE STRUTURES 3. In each set, decide which is the major resonance contributor, and explain your answer. Then draw the resonance hybrid. If charge is unequally distributed in the resonance hybrid, make that obvious with the size of the partial charges. a. These contribute equally to the resonance hybrid since in both all atoms have octets (except which has a duet) and put the negative charge on the same atom (carbon). δ+ δ+ b The structure on the right is the major contributor, as each atom has an octet. In the resonance structure on the left, one carbon atom doesn t have an octet so contributes less to the hybrid. 4. In each set, rank the resonance structures in order from most to least important to the overall resonance hybrid. Explain your answer. a b. c. MAJR (#1) #3 #2 The first structure is neutral and all atoms have an octet (besides of course which has a duet), so it contributes the most to the hybrid. The other resonance structures are charged, so contribute less. The one marked #3 is the least important because the positively charged carbon does not have an octet. #2 #3 MAJR The structure marked #3 is least important because a carbon does not have an octet. All atoms in the others structures have octets, so contribute more to the hybrid. The structure marked MAJR has the negative charge on oxygen, which is highly electronegative and stabilizes the charge better than the negative charge on the carbon in # #2 #3 MAJR The structure marked MAJR has the positive charge on nitrogen, which is less electronegative than oxygen (where the charge is on #2). The positive charge is destabilized by the oxygen in structure #2. Structure #3 has a carbon atom lacking an octet, which makes it much less important than the other two. Page 2

3 5. Draw the Lewis structure of each formula, including all possible resonance structures. Then draw the resonance hybrid, making obvious differences in partial charge. Problem Resonance ybrid a. 2 (18 val e ) (very minor) can put small d + on carbon b. 3 ( 2 ) (24 val e ) (very minor) δ+ δ- δ- can put small d + on carbon c. 2 + (12 val e ) (major) δ+ δ+ d. 3 2 (24 val e ) e. 2 (16 val e ) (major) f. 3 (22 val e ) (major) (very minor) (very minor) ~2.5 bonds can put small d + on central carbon ~2.5 bonds K if made d + instead of full + Page 3

4 6. The bond length of the - and = bond in the acetate ion (below) are equal. Explain this phenomenon, using structures with your answer Res. hybrid: 3 The acetate ion has two equal energy resonance structures that equally contribute to the resonance hybrid. There isn t a - and = which would lead to different bond lengths. The actual structure is an average of the resonance structures, and each - is a 1.5 bond, of equal length in between the length of a single and double - bond. 7. In both structures shown below the negative charge is on a nitrogen atom, but the second structure is lower in energy. Explain, using structures with your answer. 3 The right structure has RESAE which spreads the negative charge out over two atoms (,) in the molecule. Resonance is always a stabilizing effect, and charge dispersal (delocalization) is always better than having a point charge located on only one atom. Resonance makes the 2 nd structure lower energy, and more stable. YBRIDIZATI AD RBITAL DIAGRAMS 8. For each atom that is pointed to, identify the electron geometry, bond angles and hybridization of the atom. a. b. c tetrahedral, 109.5, sp 3 linear trigonal planar tetrahedral, 109.5, sp 3 180, sp 120, sp 2 d. e. f. 2 2 S linear, 180, sp tetrahedral, 109.5, sp 3 trigonal planar tetrahedral 120, sp , sp 3 Page 4

5 9. Draw an orbital diagram of each ion below using atomic and hybrid orbitals (assume all atoms are hybridized that can be). Label each orbital as s, p, sp, sp 2 or sp 3. a. b. 10. Identify the orbitals involved in each designated bond (or bonds). Assume all atoms that can hybridize do so. Label each bond as a sigma (s ) or pi (p ). a. b. c. s " sp 2 sp 2 s " sp 2 sp 2 s sp 3 sp 3 s : sp 3 sp 2 p " p p p " p p Page 5

6 LIE STRUTURES AD DESED FRMS 11. Fill in the boxes with the correct depictions of each molecule. Lewis structure ondensed Form Line Structure ( 3 ) 3 2 ( 3 ) 2 or 3 ( 3 ) 2 2 ( 3 ) 2 or 3 ( 3 ) 2 2 ( 3 ) 3 or Br 2 = 2 Br Br ( 2 )( 2 3 ) 3 2 (triple bonds are linear!) 12. Permethrin is a topical cream for the treatment of scabies (a parasitic mite that burrows under the host s skin and causes intense itching). What is the molecular formula of Permethrin? l l 3 3 : 21 : 20 l: 2 : 3 Page 6