Report Sheet Key Lewis Structures & Shapes

Chemistry Lewis Structures & Shapes KEY KEY Report Sheet Lewis Structures & Shapes Part A: Follow the instructions in the procedure to complete this table. Formula a. No. of valence electrons H2O (example) 8 c. Shape/ Molecular geometry d. Bond Angles bent 109.5° Yes No tetrahedral 109.5°° Yes No H trigonal pyramidal 109.5°° Yes No H bent/V-shaped 109.5°° Yes No trigonal planar 120°° Yes No b. Lewis Structure e. Dipole Moment H CH3Cl 14 H C Cl H NH3 8 H2S 8 H H N H S O CH2O 12 H C H 1 f. Initials (if required) Chemistry Formula SO4 2- a. No. of valence electrons b. Lewis Structure O 32 - O S O H - - 10 NO2- 18 NO2+ 16 O OCN- 16 O N2 10 O N O N O - - + N O - C d. Bond Angles tetrahedral 109.5°° Yes No linear 180°° Yes No bent/V-shaped 120°° Yes No linear 180°° Yes No linear 180°° Yes No linear N/A (no central atom) Yes No 2- C HCN Lewis Structures & Shapes KEY f. Initials e. Dipole Moment (if required) c. Shape/ Molecular geometry N - N N 2 Chemistry Formula a. No. of valence electrons SO32- 26 d. Bond Angles trigonal pyramidal 109.5°° Yes No H bent/V-shaped 109.5°° Yes No Cl bent/V-shaped 109.5°° Yes No H trigonal pyramidal 109.5°° Yes No linear 180°° Yes No tetrahedral 109.5°° Yes No b. Lewis Structure O - S + O - O Se H2Se 8 H SCl2 20 Cl PH3 8 H SCN- 16 S S P H - C Lewis Structures & Shapes KEY f. Initials e. Dipole Moment (if required) c. Shape/ Molecular geometry 2- - N - F SiF4 32 F Si F F 3 Chemistry Formula a. No. of valence electrons OF2 20 F CSe2 16 Se ClO4 - O 32 26 bent/V-shaped 109.5°° Yes No linear 180°° Yes No tetrahedral 109.5°° Yes No trigonal pyramidal 109.5°° Yes No H tetrahedral 109.5°° Yes No Cl trigonal pyramidal 109.5°° Yes No O F C O Se - - Cl O O NI3 d. Bond Angles b. Lewis Structure - - - N I I I + H NH4+ + 8 H N Lewis Structures & Shapes KEY f. Initials e. Dipole Moment (if required) c. Shape/ Molecular geometry H PHCl2 20 H P Cl 4 Chemistry Lewis Structures & Shapes KEY Part B: Answer each question below. Refer to models if you find them helpful. 1. There are three different ways that you can make a molecule with formula C2H2Cl2. Draw all three. Below each, either draw an arrow indicating the direction of the dipole moment or write “no dipole moment” if there is none. In each case, carbon should make four bonds, while hydrogen and chlorine make one bond. H H C Cl C Cl Cl H C H H C Cl C Cl H C Cl no dipole moment 2. Two students are asked to draw the Lewis structure for CH2Cl2 and state whether or not the molecule has a dipole or not. Their answers are shown below. Both students’ Lewis structures are correct since it doesn’t matter which atoms are drawn in each direction. However, only one student is correct about the dipole. Does CH2Cl2 have a dipole? If so, clearly draw the dipole. Also, explain why one of the students was wrong, and describe how you could convince them of the correct answer. Answer with complete sentences. Student 1’s drawing implies that CH2Cl2 had no dipole moment since the most electronegative atoms are on opposite sides of the molecule. However, the molecule does indeed have a dipole moment. The two-dimensional Lewis Structures do not give an accurate representation of the molecule’s polarity. The three-dimensional structure shown below shows the dipole moment. By building a model it should be easy to show that the shape of the molecule is tetrahedral and that the polarity in the two C-Cl bonds do not cancel. Cl H H Cl 5 Chemistry Lewis Structures & Shapes KEY 3. For each of the two polyatomic ions below, there is more than one way you can draw the structures by moving the positions of electrons in bonds and lone pairs. Each of these drawings is called a resonance structure for the molecule. Draw the indicated number of resonance structures for each ion. a. NO3- (nitrate ion – three resonance structures) Note that these three resonance structures should look like the same structure rotated 120°. We call these equivalent resonance structures to indicate that the bonding patterns are the same. O O + - N O O - - + - O N O O - - + - O - N O b. OCN- (cyanate ion – two resonance structures, although more are possible) O C + N - O + C + - N Another resonance structure for cyanate ion is shown on the second page of the report sheet.