Chemistry 123. T, Th 1:00pm 2:15pm & 2:30pm 3:45pm Examination #2 November 22 nd Bronco ID. Question Score Possible Points. 1 (10pts) 3 (28pts)

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1 Chemistry 123 T, Th 1:00pm 2:15pm & 2:30pm 3:45pm Examination #2 November 22 nd 2016 Name Bronco ID. Question Score Possible Points 1 (10pts) 2 (28pts) 3 (28pts) 4... (34pts). Total (100pts) 1. Read each question carefully. Make sure you are answering the question which is being asked. Write your answer clearly or draw a box around it. 2. Answer easier questions first, more difficult questions later 3. Ask the instructor for clarification if you are puzzled by the question 4. Show work for credit. Use dimensional analysis by meant of using an appropriate stoichiometry and formulas to prove your work. Watch for significant figures. 5. Any forms of cheating will be an automatic F 6. GOOD LUCK 1

2 Question I (10pts) Multiple choice: Choose one best answer 1. Which of the following statements is TRUE? A) The total number of molecular orbitals formed doesn't always equal the number of atomic orbitals in the set. B) A bond order of 0 represents a stable chemical bond. C) When two atomic orbitals come together to form two molecular orbitals, one molecular orbital will be lower in energy than the two separate atomic orbitals and one molecular orbital will be higher in energy than the separate atomic orbitals. D) Electrons placed in antibonding orbitals stabilize the ion/molecule. E) All of the above are true. 2. A molecule containing a central atom with sp3d2 hybridization has a(n) electron geometry. A) octahedral B) trigonal pyramidal C) tetrahedral D) linear E) tirgonal planar 3. Which of the following is not a valence bond concept? A) The greater the overlap between the orbitals on two atoms, the stronger the bond. B) Lone pair electrons are in atomic orbitals or in hybrid atomic orbitals. C) Atomic orbitals on two atoms may overlap to form antibonding orbitals. D) A pair of electrons in a bond is shared by both atoms. 4. Identify the compound that does not have hydrogen bonding. A) (CH3)3N B) H2O C) CH3OH D) HF E) CH3NH2 5. What type of intermolecular force causes the dissolution of KF in water? A) hydrogen bonding B) dipole-dipole forces C) ion-dipole force D) dispersion forces E) none of the above 6. Arrange the following in order of increasing boiling point. CH3CH2OH CH3CH2CH3 H3C-O-CH3 CH3CH2NH2 I II III IV A) IV < III < II < I B) II < III < IV < I C) I < IV < III < II D) II < III < I < IV 2

3 7. In the drawing of acetaldehyde, CH3CHO, the largest partial positive charge (δ+) occurs on A) atom (a). B) atom (b). C) atom (c). D) atom (d). Answer: B 8. Nuclides above the valley of stability can become more stable through which of the following processes? A) beta emission B) positron emission C) gamma emission D) electron capture E) neutron bombardment 9. Which of the following statements about positrons is false? A) The positron has same mass as an electron. B) A positron is ejected from the nucleus during the conversion of a proton into a neutron. C) A positron is a positive electron. D) When positron emission occurs, the atomic number of the nucleus increases. 10. Which one of the following combinations of neutrons/protons results in the lowest number of nonradioactive (stable) isotopes? A) even number protons/even number neutrons B) even number protons/odd number neutrons C) odd number protons/even number neutrons D) odd number protons/odd number neutrons Bonus: (5pts) Show a bonding picture of how hybrid orbitals are overlapping in the following molecule. Indicate the π and σ bond formation. 3

4 Question II-28pts 1. (5pts) The percent ionic character for Na-Cl in the gas phase is 80.0%. Explain how does this percentage implied to the dipole between Na-Cl bond. 2. (4pts) Why is the dipole moment of SO 2 is 1.63 D, but that of CO 2 is zero? 3. (2pts) The splitting of the nucleus into lighter nuclei is called.? 1. (6pts) What is hybridization? Can two 2p orbitals of an atom hybridize to give two hybridized orbitals? Describe a hybrid orbital of sp 2 4. (5pts) What is the ratio of n/p (e.g less n, more p or more n, less p) to those atoms that below the belt of stability? What type(s) of emission will they undergo to become stable? 5. (6pts) Describe the process of electron capture. What happens to the mass number and atomic number of a nuclide that undergoes electron capture? 4

5 Question III Nuclear chemistry (28pts) 1. (9pts) Complete the following nuclear reactions and state the type of radioactive decay: a. b. c. + He Bk + 2 n 2. (5pts) Rutherfordium-257 (Rf-257) and other radioactive particle(s) were synthesize by bombarding Cf-249 with C-12. Write the nuclear equation for this reaction 1. (6pts) One of the nuclides in spent nuclear fuel is U-235, an alpha emitter with a half-life of 7.03 x 10 9 years. How long will take for the amount of U-235 to reach 41.0% of its initial amount? An appropriate equation must be used to solve for this problem. NO short cut!!!! 3. (8pts) What is the energy change E (in MeV/mol) when an particle is emtted from Ir-174. The atomic mass of Ir-174 is amu, the atomic mass of Re-170 is amu, and the atomic mass of a He-4 atom is amu 5

6 Question IV VSEPR theory, Valence Bond theory and Vapor Presssure (34pts) 1) (6pts) The Br Cl bond has 5.05% ionic character and a dipole moment of D. What is the distance (in pm) between atoms in BrCl? 2) (8pts) Draw two resonance contributors of SOCl 2 and a resonance hybrid 3) (20pts) Complete the following tables Molecular formula Lewis structure Molecular shape around the central atom Hybridization(s) Number of σ bond(s) Number of π bond(s) Molecular polarity PCl 6 - NBr 3 6

7 Potentially useful information Q = 1.60 x C 1 D =3.34 x C m 1 m = pm R = J/mol K 1 amu = x g 1 MeV = x J Proton Mass amu Neutron Mass amu Electron Mass amu Avogadro s number = 6.02 x per mol 7

Chemistry 201. MW 12pm 1:15pm Examination #1 July 20 th Bronco ID. Question Score Possible Points. 1 (17pts) 2 (28pts) 3 (14pts) 4...

Chemistry 201. MW 12pm 1:15pm Examination #1 July 20 th Bronco ID. Question Score Possible Points. 1 (17pts) 2 (28pts) 3 (14pts) 4... Chemistry 201 MW 12pm 1:15pm Examination #1 July 20 th 2016 Name Bronco ID. Question Score Possible Points 1 (17pts) 2 (28pts) 3 (14pts) 4... (22pts) 5 (19pts). Total (100pts) 1. Read each question carefully.