chem2110-mid1-f22

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Chemistry

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CHEM 2110 MIDTERM EXAM 1 FALL 22 COVER SHEET COVER SHEET MAY BE TORN OFF THE EXAM AND USED FOR REFERENCE

2 CHEM 2110 MIDTERM EXAM 1 FALL 22 NAME:_______________ DATE:________________ YOU HAVE 90 MINUTES. NO CALCULATORS OR OTHER ELECTRONIC DEVICES MAY BE USED DURING THE EXAM. YOU MAY USE ONE 8.5”x11” PAGE OF NOTES AND A MODEL KIT, BUT YOU ARE RESPONSIBLE FOR KEEPING BOTH OF THESE OUT OF EASY VIEW OF YOUR CLASSMATES. PERIODIC TABLE AND REFERENCE DATA MAY BE TORN OFF OF EXAM. 25 QUESTIONS, 100 POINTS TOTAL + 4 POINTS EXTRA CREDIT 1. (10 points) Indicate whether each of the following statements is true or false. a. ______A molecule with an even number of electrons cannot be paramagnetic. b. ______Doubling the amplitude of a wave doubles its wavelength. c. ______A 2p-orbital contains a nodal plane. d. ______Hund’s Rule applies to atomic orbitals but not to molecular orbitals. e. ______No two wavefunctions in an atom can have the same energy. f. ______A double bond contains a sigma bond. g. ______An sp 3 -hybridized atom cannot form a pi bond. h. ______A lone pair of electrons cannot occupy a sp 2 -hybrid orbital. i. ______The formal charge of an atom can never be less than zero. j. ______All aromatic molecules contain sigma bonds. 2. (2 points) Consider the following sets of quantum numbers. Circle all of the allowed sets of quantum numbers for an electron in a hydrogen atom. The electron may be either in a ground state or an excited state. Circle all that apply. n=3, l =2, m l =-1, m s =+1/2 n=2, l = - 1, m l =-1, m s = - 1/2 n=1, l =1, m l =1, m s = - 1/2 n=4, l =3, m l =3, m s =+1/2 None of these sets of quantum numbers are allowed. 3. (3 points) What is the bond order of a molecule with the configuration: ( σ 2s ) 2 ( σ 2s * ) 2 ( σ 2px ) 2 ( π 2py , π 2pz ) 4 ( π ∗ 2py , π ∗ 2pz ) 4 ( σ 2px * ) 2 Answer:________

3 4. (3 points) Draw a resonance structure for the molecule shown. It must be a valid structure, and it must be appropriate to draw it under the usual rules for resonance structures. Draw only one structure; if you draw two and either is incorrect, you will receive no credit for the problem. 5. (3 points) Write the full electronic configuration for the following atoms or ions. Do not abbreviate using noble gas configurations. Cl + : 6. (4 points) Which of the following molecules are polar? Circle all that apply: HCN BH 3 CCl 4 F 2 7. (3 points) Circle the most polar bond from the list: H-O H-S H-N 8. (3 points) Which atom or ion has the largest radius? Circle one. Si Si + C S 9. (3 points) What is the best estimate for the O-S-O bond angle in a SO 2 molecule? Circle one: 90 o Slightly less than 90 o Slightly more than 90 o 109.5 o Slightly less than 109.5 o Slightly more than 109.5 o 120 o Slightly less than 120 o Slightly more than 120 o 180 o Slightly less than 180 o Slightly more than 180 o

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4 10. (12 points) Give Lewis structures for each of the following molecules or ions. Make sure to include all lone pairs. If the molecule displays resonance, draw all contributing structures. a. C 2 H 2 ( Hint: Each C is bonded to one H atom ) b. BF 4 - 11. (3 points) Give the formal charge of the *’ed carbon and nitrogen atoms in the Lewis structure below: Carbon:_____ Nitrogen:____

5 12. (3 points) Draw the resonance stucture indicated by the push notation below: 13. (3 points) Identify the molecular geometry of NCN 2- (C is the central atom). Circle the correct answer. NCN 2- : Circle one: Bent Linear Octahedral Tetrahedral Seesaw-shaped Square Planar Square Pyramidal T-Shaped Trigonal Bipyramidal Trigonal Planar Trigonal Pyramidal 14. (4 points) Some of the molecules and ions given below are planar (i.e. all atoms in the molecule are in the same plane). Circle all of the molecules that are planar. Circle all that apply. Note that structures indicate bonds but do not indicate lone pairs (i.e. they are not full Lewis structures). H 2 C=NH H 2 C=C=CH 2 NI 3 CH 3 -CH 3 15. (3 points) For the structure below, circle all of the atoms that contain at least one unhybridized p-orbital.

6 16. (5 points) Which of the following statements is true based on the Lewis structure shown below? Circle all that apply. a. All atoms in the ion are within the same plane. b. Both oxygen atoms are sp 2 -hybridized. c. The carbon that is bound to the oxygen has exactly two unhybridized p-orbitals. d. Both of the C-O bond lengths are the same. e. There is one unhybridized p-orbital on each oxygen, and they are parallel to each other. f. Both of the Lewis structures shown are valid for this molecule, and they are equally significant. g. None of these statements is true. 17. (5 points) Answer each of the following about the molecule shown below. a. (1 pt) Give the hybridization of the carbon labeled α :_____ b. (1 pt) Give the hybridization of the carbon labeled β :_____ c. (1 pt) Give the hybridization of the nitrogen:_____ d. (2 points) How many pi bonds are in the molecule shown in part a above? Give the total number in the entire molecule. Ans:_______

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7 18. (3 points) Which of the answers below is the best estimate of the angle indicated by α in the diagram below? 90 o Slightly less than 90 o Slightly more than 90 o 109.5 o Slightly less than 109.5 o Slightly more than 109.5 o 120 o Slightly less than 120 o Slightly more than 120 o 180 o Slightly less than 180 o Slightly more than 180 o None of these is close 19. (5 points) A molecular orbital diagram is given below. Use it to answer each of the following: a. (2 points) Use Aufbau rules to fill in the electrons in the diagram to show the electron configuration for C 2 2- (i.e. draw the arrows onto the diagram). b. (2 points) What is the bond order of C 2 2- ? Answer:________ c. (1 points) Is the molecule paramagnetic? Circle one: Yes No

8 20. (4 points) A molecular orbital diagram is given to the right. It corresponds to a cation with the formula X 2 + , where X is a 2 nd row element. Use it to answer each of the following questions. a. (1 pt) Identify the element X (i.e. give its atomic symbol). Ans:_______ b. (1 pt) Calculate the bond order. Ans:______ c. (2 pt) Write the molecular orbital configuration shown. Answer:__________________________ 21. (3 points) Which of the following statements is true based on the Lewis structure shown below? Circle all that apply. a. All of the atoms in this molecule are in the same plane. b. There are 4 sigma bonds in the molecule. c. The nitrogen is sp 2 -hybridized. d. None of these statements are true. 22. (3 points) Circle the image below that represents a π * molecular orbital in a diatomic molecule:

9 23. (3 points) Which of the structures I-III are valid resonance structures of the first molecule shown? Indicate only whether the structure is a valid resonance structure, not its relative significance. Circle all valid structures. 24. (4 points) Which of the molecules shown below should be more stable? Justify your answer in no more than 4 sentences. You must justify your answer to receive credit. More stable structure:_______ Justification:

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10 25. (3 points) Which of the resonance structures below is the most significant, and which is the least? Enter your answer in the space provided. Most significant:_________ Least significant:_________ (4 points – EXTRA CREDIT) Consider the molecule SO 3 and the anion SO 3 - 2 . Which has a larger O-S-O bond angle? Justify your answer in no more than 4 sentences. ( Hint: Use Lewis structures!)