UNIVERSITY OF VICTORIA. CHEMISTRY 101 Mid-Term Test 2, November

Transcription

1 NAME Student No. SECTIN (circle one): A01 (Codding) A02 (Sirk) A03 (Briggs) Version A UNIVERSITY F VICTRIA CEMISTRY 101 Mid-Term Test 2, November Version A This test has two parts and 8 pages, including the cover page. Please count the pages to ensure you have them all. PART I is a multiple choice section and is worth 24 marks. The answers for the 13 questions in this part must be coded on the optical sense form using a SFT PENCIL. PART II consists of written answers and is worth 26 marks. Answer these questions on this examination paper. Answers written partially or completely in pencil cannot be remarked. - and in this entire test paper as well as your optical sense form (i.e. bubble sheet) at the end of the examination period (60 minutes). -The basic Sharp EL510 calculator is the only one approved for use in Chemistry A DATA sheet accompanies this test. Marks for Written Answers Question 1 [6] Question 2 [6] Question 3 [4] Question 4 [5] Question 5 [5] TTAL (/26) Multiple Choice (/24) Raw Score (/50) TTAL MARK (%)

2 Chemistry 101, Mid-Term Test 2 Fall 2010 Version A page 2 of 8 PART I Multiple Choice: Select the BEST response for each question below. [Total marks = 24] 1. This is exam Version A. Mark A as the answer to Question 1 on the optical sense form. 2. Choose the CRRECT statement about the S 2 molecule. A. The sulfur atom has an unshared (i.e. non-bonding) electron pair. B. The S- bonds are ionic in character. C. The two S- bonds have different lengths since one is a single bond and the other a double bond. D. The molecule has a linear structure. E. The oxygen atoms have no unshared (i.e. non-bonding) electron pairs. Questions 3-6 refer to the molecules in this box. Answer these questions referring to these answers. i. Si4 ii. BF3 iii. F2 iv. NF3 v. N vi. BrF5 vii. XeF4 viii. CCl 2 3. Indicate all of the molecules in the box above that have a molecular structure best described as involving an incomplete octet? A. i only B. ii & v C. v only D. ii & iv E. vii only 4. Indicate all of the molecules in the box above that have both an electron group geometry (electron domain geometry) and a molecular geometry that are trigonal planar (triangular planar)? A. i & vii B. ii only C. iii only D. ii & viii E. iv only 5. Indicate all of the molecules in the box above that have a square pyramidal molecular shape? A. i B. vii C. vi D. ii E. iv 6. Indicate all of the molecules in the box above that have at least one bond angle of about 90? A. ii only B. iv only C. vii only D. vi & vii E. ii & iv 7. Consider the following three molecules. Which molecule(s) is(are) polar? (That is, which molecules have a non-zero net molecular dipole moment?) BF 3 NF 3 CF 4 A. BF 3 only B. NF 3 only C. CF 4 only D. both BF 3 and NF 3 E. none of them

3 Chemistry 101, Mid-Term Test 2 Fall 2010 Version A page 3 of 8 8. The electron-domain geometry of a sulfur-centered compound is trigonal bipyramidal. The hybridization of the central sulfur atom is. A. sp B. sp 2 C. sp 3 D. sp 3 d E. sp 3 d 2 9. Which of the following statements is INCRRECT? A. A linear arrangement of electron domains can often be rationalized using sp hybrid orbitals.. B. When assigning the orbital hybridization, only bonding electrons are considered, since lone pairs do not participate in hybridization. C. An octahedral molecular geometry is rationalized by the hybridization of six atomic orbitals. D. Double bonds take up more space than single bonds. E. In NF 3 there are bond angles that are slightly less than the regular tetrahedral angle of The hybridizations of bromine in BrF 5 and of iodine in ICl 3 are and ; respectively. A. sp 3, sp 3 d B. sp 3, sp 3 d 2 C. sp 3 d, sp 3 D. sp 3 d 2, sp 3 d E. sp 3 d, sp 3 d A Lewis structure of the aspirin molecule is shown below. The approximate bond angles (in degrees, o ) for the bonds labeled a, b and c in the drawing are, respectively? a b c C C C 3 A. 120, 120, 120 B. 120, 109, 180 C. 180, 120, 120 D. 120, 120, 109 E. 109, 109, 120

4 Chemistry 101, Mid-Term Test 2 Fall 2010 Version A page 4 of Which of the following statements is CRRECT for metallic bonding? i. Bonding electrons in metals are free to move throughout the metal. ii. The electron-sea model explains the trends in melting points for the transition metals. iii. The energy gap between bonding and antibonding molecular orbitals is largest for an insulator. iv. There are no antibonding molecular orbitals for a semiconductor. A) i B) i and ii C) ii and iii D) i and iii E) ii and iv 13. Consider the following molecular orbital energy diagram, which applies to diatomic species that use only 1s orbitals. molecular orbitals atomic orbital atomic orbital The M diagram shown above can represent the electron energy levels for which molecule(s) or ion(s)? i. 2 ii. e 2 + iii. e 2 iv. e v. 2 A. i only B. ii only C. iv only D. i, ii and iv E. ii, iii and iv

5 Chemistry 101, Mid-Term Test 2 Fall 2010 Version A page 5 of 8 PART II Written Answer Questions. [Total Marks = 26] Write your answers directly on this test paper. Show all your work. This helps us to award part marks instead of zero where appropriate. and in the entire test paper at the end of the test period. [6 marks] 1. [3] a) Use average bond energies from the datasheet to estimate the enthalpy change for the following reaction. Note that the carbon atoms are bonded to one another in both C 2 4 and C (g) + C 2 4 (g) C 2 6 (g) break - bond and C=C bond, make C-C bond and two C- bonds Delta rxn = 432 kj/mol kj/mol [2(413 kj/mol) kj/mol] = -128 kj/mol Datasheet gives: -* 432, C- 413, C C 348, C=C 614 [1] b) Which of the compounds in (a) has the longer carbon-carbon bond? Explain. C 2 6 has a longer C-C bond because it is a single bond. [2] c) ow many sigma (σ) and pi (π) bonds are present in the entire molecule C 2 4?: 5 sigma bonds 1 pi bonds

6 Chemistry 101, Mid-Term Test 2 Fall 2010 Version A page 6 of 8 [6 marks] 2. [2] a) The ion I - 3 is known but the ion F - 3 is not. Draw the Lewis structures for the two ions and explain why F - 3 does not form. I I I F F F Not possible for fluorine. Breaks octet rule & some comment about F not being able to expand its valence shell since it is in row 2 and doesn t have empty d orbitals [4] b) Use VSEPR theory to predict the shape of the I 3 - ion and state which set of hybrid orbitals would be used for the central iodine atom. Draw a three-dimensional representation of the hybrid orbitals and the molecular shape. What is the value of the I-I-I bond angle? VSEPR shape for electron domains is trigonal bipyramidal, sp 3 d (or dsp 3 ) hybrid, molecular shape is linear, I I I 180 o bond angle. 4 marks 3. For each of the three oxides C 2, S 2 and Xe 3, make a three-dimensional sketch of the molecule and clearly indicate which one(s) is(are) polar. (That is, state which ones have a non-zero net molecular dipole moment.) Note: Your sketch does not have to be a complete Lewis structure, but it does need to correctly represent the shape of the molecule. For each structure, draw an arrow to indicate the net molecular dipole moment.

7 Chemistry 101, Mid-Term Test 2 Fall 2010 Version A page 7 of 8 [5 marks] 4. In nitryl chloride, 2 NCl (overall neutral molecule), the chlorine atom and the two oxygen atoms are bonded to the central nitrogen atom. a) Draw all resonance structure(s) for 2 NCl assuming that the octet rule holds for all atoms. Show each bonding pair of electrons as a line ( ) and show non-bonding valence electrons as dots (:). b) Show any non-zero formal charges on each atom in all the structures that you draw. Answer a and b Cl N Cl N Cl N c) What is the bond order of a nitrogen-oxygen bond in this molecule? Answer c Nitrogen-oxygen bond order is 1.5

8 Chemistry 101, Mid-Term Test 2 Fall 2010 Version A page 8 of 8 [5 marks] 5. Consider the nitroxyl molecule N Draw (i.e. sketch) all of the orbitals used to form ALL sigma (σ) bonds and pi (π) bonds in this molecule, as well as any orbitals containing lone pairs of electrons. Show clearly how the orbitals overlap to form bonds. Label all the orbitals and bonds. (For clarity of presentation you may show the sigma (σ) and pi (π) bonding separately using two diagrams.) *********************************END***************************************