Chemistry Exam Questions: Atomic Structure and Molecular Orbitals - Prof. Martin H. Gruebe, Exams of Chemistry

Download Chemistry Exam Questions: Atomic Structure and Molecular Orbitals - Prof. Martin H. Gruebe and more Exams Chemistry in PDF only on Docsity! Chem 202 Practice Hour Exam I for Oct. 2008 Prof. Gruebele Instruction Page Name: Signature: Student ID No: Quiz Sect: TA: The midterm will contain 21 multiple choice questions (4 pts. ea.) and one word problem (16 pts.), similar to the examples shown here. Fill in your name, signature, student ID no., quiz section and TA name above. On the bubble answer sheet fill in the same type of information; use just the two "important" digits of your quiz section under "class" and follow instructions on the board. Failure to fill in all information may delay grading of your exam. You may write on any part of the exam; however, only bubbles filled in on the answer sheet will count as credit for the multiple choice questions; only answers written in the boxed spaces provided on the exam will count for the essay question. Turn in the exam and the answer sheet at the end of the hour. For rough work, use only the loose sheets provided. Work on loose sheets will not be collected, and will not be counted. The exam booklet will be returned to you next quiz section. Instructions: Do not begin the exam until you are told to do so; in the meantime, fill in the information requested below. Practice exam time: 30 minutes, relative to 1 hr. on actual exam PAGE 2 8) Consider the HF+ molecule. Which MO diagram showing 1s(H) and 2pz(F) orbitals best describes the bonding? a) b * b) b * c) b * d) b * e) b * Chem 202 Fall 2008 Hour Exam I 10-08Name: TA: Section: 9) When a drum is hit near the edge, a) The pitch is lower because a wavefunction with higher energy is excited b) The pitch is higher because a wavefunction with more nodes is excited c) The pitch is lower because the drum behaves like a two dimensional version of a hydrogen atom d) The pitch is higher because the energy associated with the motion of the drum head is higher e) b and d 10) Mountain Dew looks green-yellow because it contains a dye that absorbs all the violet light. In Joules, roughly what is the spacing between the electronic energy levels of the dye across which the absorbing electron hops? a) 5.10-50 b) 5.10-19 c) 0.001 d) 2.1018 e) 1.1048 11) Real chain molecules ar not like perfect boxes; the walls are somewhat "soft" because the electrons can move past the nuclei by 0.5-1 Å. Which of the following properly best describes the potential energy and energy levels of such a box? (The perfect box and levels are shown dotted for reference.) a) b) c) d) e) none of these is even close 12) Which of the following statement(s) are correct: a) The Pauli exclusion principle applies only to electrons, not to protons. b) Two electrons cannot be in the same quantum state, with all quantum numbers the same c) The Heisenberg principle states that quantum particles occupy an "elbow room" of area h, and the Pauli principle states that these "elbow rooms" cannot overlap d) b and c e) a,b and c Chem 202 Fall 2008 Hour Exam I 10-08 PAGE 1 1) The atomic number of which element is 16? a) oxygen b) potassium c) sulfur d) phosphorus e)none of these b) 2) Which of these is a reasonable potential energy curve for NO? r 0 0 V(r) d) r 0 0 V(r) e) (ii) In question 3, what hybridization best describes the atom shown labeled (labels refer to N,C or O, not any H's that are not shown) H N N H HO H C=CH2 4) Which of the following orderings is in terms of DECREASING atomic radius? a) Ca++, K+, Ar, Cl- b) Ar, K+, Ca++, Cl- c) Cl-, Ca++, K+, Ar d) Cl-, Ar, K+, Ca++ e) none 5) Blood plasma contains approximately 7% by mass of the protein albumin. How many moles of this protein are contained in 1 liter of blood plasma? (M.W. (albumin) = 69,000 grams/mole; density of blood plasma = 1.06 kg/liter.) a) 9.57.10-4 b) 1.01.10-3 c) 986 d) 992 e) 1.08.10-3 6) What is the elctron configuration of Scandium? a) [Ar] 4s23d1 b) [Ar] 3s23d1 c) [Ar]4s3 d) [Ar]3s22d1 e)[Kr]-4s23d1 7) The laser in a CD player (which reads reflective grooves on the CD surface) has a wavelength of 780 nanometers. What is the energy of a single photon from this CD player in Joules? a) 1.7.10-50 b) 1.7.10-45 c) 2.6.10-26 d) 2.6.10-19 e) none of these Note: the actual MOs are distorted from the atomic shapes much more, but this type of sketch is acceptable as an answer on the hour exam. Note: no transition metals on exam! Chem 202 Practice Hour Exam I for Oct. 2008 Prof. Gruebele Instruction Page The midterm will contain 21 multiple choice questions (4 pts. ea.) and one word pr bl m (16 pts.), similar to the examples shown here. Fill in you name, signature, student ID no., quiz section and TA nam above. On the bubble answer sheet fill in the same type of information; us just the two "i portant" digits of your quiz section under "class" and follow instructions on the board. Failure to fill in all information may delay grading of your exam. You may write on any part of the exam; however, only bubbles filled in on the answer sh et will co nt a credit for the multiple choice questions; only answers written in the boxed spaces provided on the exam will count for the essay question. Turn in the exam and the answer sheet at the end of the hour. For rough work, use only the loose sheets provided. Work on loose sheets will not be collected, and will n t be counted. The exam booklet will be returned to you next quiz section. Instructions: Do not begin the exam until you are told t d so; in the me ntime, fill in the information requested below. Practice exam time: 30 minutes, relative o 1 hr. on actual exam PAGE 2 8) Consider the HF+ molecule. Which MO diagram showing 1s(H) and 2pz(F) orbitals best describes the bonding? a) b * b) b * c) b * d) b * e) b * Chem 202 Fall 2008 Hour Exam I 10-08Name: TA: Section: 9) When a drum is hit near the edge, a) The pitch is lower because a wavefunction with higher energy is excited b) The pitch is higher because a wavefunction with more nodes is excit d c) The pitch is lower because the drum behaves like a two dimensional version of a ydrogen atom d) The pitch is higher because the energy associated with the motion of the drum head is higher e) b and d 10) Mountain Dew looks green-yellow because it contains a dye that absorbs all the violet light. In Joules, roughly what is the spacing between the electronic energy levels of the dye across whi h the absorbing electron hops? a) 5.10-50 b) 5.10-19 c 0.0 1 d) 2.1018 e) 1. 048 11) Real chain molecules ar not like perfect box s; the walls are somewhat "soft" b ause the el ctrons can move past the nuclei by 0.5-1 Å. Which of the following properl best describes the pot ntial energy and energy levels of such a box? (The perfect box and levels are s own dotted for ref rence.) a) b) c) d) e) none of these is even close 12) Which of the following statement(s) are correct: a) The Pauli exclusion principle applies only to lectrons, not to protons. b) Two electrons cannot be in the same quantum state, with all quantum numbers the same c) The Heisenberg principle states that quantum part cles occupy an " lbow room" of area h, and the Pauli principle states that these "elbow rooms" can ot overlap d) b and c e) a,b and c Chem 202 Fall 2008 Hour Exam I 10-08Name: TA: Section: PAGE 1 1) The atomic number of which element is 16? a) oxygen b) potassium c) sulfur d) phosphorus e)none of these r 0 0 V(r) a) r 0 0 V(r) b) 2) Which of these is a reasonable potential energy curve for NO? r 0 0 V(r) c) r 0 0 V(r) d) r 0 0 V(r) e) (ii) In question 3, what hybridization best describes the atom shown labeled (labels refer to N,C or O, not any H's that are not shown) 3) atom (ii): a) sp b) sp c) sp3 2 H H CO3 N N H HO H C=CH2 4) Which of the following orderings is in terms of DECREASING at mic radiu ? a) Ca++, K+, Ar, Cl- b) Ar, K+, Ca++, Cl- c) Cl-, Ca++, K+, Ar d) Cl-, Ar, K , a++ e) none 5) Blood plasma contains approximately 7% by mass of the protein albumin. How many mole is protein are contained in 1 liter of blood plasma? (M.W. (albumin) = 69,000 grams/mole; density of blood plasma = 1.06 kg/liter.) a) 9.57.10-4 b) 1.01.10-3 c) 986 d) 992 e) 1.08.10-3 6) What is the elctron configuration of Scandium? a) [Ar] 4s23d1 b) [Ar] 3s23d1 c) [Ar]4s3 d) [Ar]3s22d1 e)[Kr]-4s23d1 7) The laser in a CD player (which reads reflective grooves on the CD surface) ha a wavelen th f 780 nanometers. What is the energy of a single ph ton f om this CD player in Joules? a) 1.7.10-50 b) 1.7.10-45 c) 2.6.10-26 d) 2.6.10-19 e) none of these Note: the actual MOs are distorted from the atomic shapes much more, but this type of sketch is acceptable as an answer on the hour exam. Note: o transition metals on exam! Chem 202 Practice Hour Exam I for Oct. 2008 Prof. Gruebele Instruction Page The midterm will contain 21 multiple choice questions (4 pts. ea.) and one word problem (16 pts.), similar to the examples shown here. Fill in your name, signature, student ID no., quiz section and TA name above. On the bubble answer sheet fill in the same type of information; use just the two "important" digits of your quiz section under "class" and follow instructions on the board. Failure to fill in all information may delay grading of your exam. You may write on any part of the exam; however, only bubbles filled in on the answer sheet will count as credit for the multiple choice questions; only answers written in the boxed spaces provided on the exam will count for the essay question. Turn in the exam and the answer sheet at the end of the hour. For rough work, use only the loose sheets provided. Work on loose sheets will not be collected, and will not be counted. The exam booklet will be returned to you next quiz section. Instructions: Do not begin the exam until you are told to do so; in the meantime, fill in the information requested below. Practice exam time: 30 minutes, relative to 1 hr. on actual exam PAGE 2 8) Consider the HF+ molecule. Which MO diagram showing 1s(H) and 2pz(F) orbitals best describes the bonding? a) b * b) b * c) b * d) b * e) b * Chem 202 Fall 2008 Hour Exam I 10-08Name: TA: Section: 9) When a drum is hit near the edge, a) The pitch is lower because a wavefunction with higher energy is excited b) The pitch is higher because a wavefunction with more nodes is excited c) The pitch is lower because the drum behaves like a two dimensional version of a hydrogen atom d) The pitch is higher because the energy associated with the motion of the drum head is higher e) b and d 10) Mountain Dew looks green-yellow because it contains a dye that absorbs all the violet light. In Joules, roughly what is the spacing between the electronic energy levels of the dye across which the absorbing electron hops? a) 5.10-50 b) 5.10-19 c) 0.001 d) 2.1018 e) 1.1048 11) Real chain molecules ar not like perfect boxes; the walls are somewhat "soft" because the electrons can move past the nuclei by 0.5-1 Å. Which of the following properly best describes the potential energy and energy levels of such a box? (The perfect box and levels are shown dotted for reference.) a) b) c) d) e) none of these is even close 12) Which of the following statement(s) are correct: a) The Pauli exclusion principle applies only to electrons, not to protons. b) Two electrons cannot be in the same quantum state, with all quantum numbers the same c) The Heisenberg principle states that quantum particles occupy an "elbow room" of area h, and the Pauli principle states that these "elbow rooms" cannot overlap d) b and c e) a,b and c Chem 202 Fall 2008 Hour Exam I 10-08 PAGE 1 1) The atomic number of which element is 16? a) oxygen b) potassium c) sulfur d) phosphorus e)none of these b) 2) Which of these is a reasonable potential energy curve for NO? r 0 0 V(r) d) r 0 0 V(r) e) (ii) In question 3, what hybridization best describes the atom shown labeled (labels refer to N,C or O, not any H's that are not shown) H N N H HO H C=CH2 4) Which of the following orderings is in terms of DECREASING atomic radius? a) Ca++, K+, Ar, Cl- b) Ar, K+, Ca++, Cl- c) Cl-, Ca++, K+, Ar d) Cl-, Ar, K+, Ca++ e) none 5) Blood plasma contains approximately 7% by mass of the protein albumin. How many moles of this protein are contained in 1 liter of blood plasma? (M.W. (albumin) = 69,000 grams/mole; density of blood plasma = 1.06 kg/liter.) a) 9.57.10-4 b) 1.01.10-3 c) 986 d) 992 e) 1.08.10-3 6) What is the elctron configuration of Scandium? a) [Ar] 4s23d1 b) [Ar] 3s23d1 c) [Ar]4s3 d) [Ar]3s22d1 e)[Kr]-4s23d1 7) The laser in a CD player (which reads reflective grooves on the CD surface) has a wavelength of 780 nanometers. What is the energy of a single photon from this CD player in Joules? a) 1.7.10-50 b) 1.7.10-45 c) 2.6.10-26 d) 2.6.10-19 e) none of these Note: the actual MOs are distorted from the atomic shapes much more, but this type of sketch is acceptable as an answer on the hour exam. Note: no transition metals on exam! "22)" Written problem Only answers in the boxes will be counted for PAGE 3 Chem 202 Fall 2008 Hour Exam I 10-08Name: TA: Section: The molecule NO (nitric oxide) is formed in the oxidation of nitrogen in car engines, and further oxidizes to higher nitric oxides (e.g. NO2), all of which are toxic atmospheric contaminants. a) fill the MO diagram in the box with the correct number of electrons for NO b) b') b) sketch one of the "b)" and the "b')" orbitals labeled in the box to the right in the box below: b) b') c) Is liquid NO paramagnetic or diamagnetic? Note: this word problem is about 1/2 the length of the one on the midterm; also, the midterm has 22 multiple choice questions, not 12, covering the same range from easy to difficult. Chem 202 Practice Hour Exam I for Oct. 2008 Prof. Gruebele Instruction Page The midterm will contain 21 multiple choice questions (4 pts. ea.) and one word pr bl m (16 pts.), similar to the examples shown here. Fill in you name, signature, student ID no., quiz section and TA nam above. On the bubble answer sheet fill in the same type of information; us just the two "i portant" digits of your quiz section under "class" and follow instructions on the board. Failure to fill in all information may delay grading of your exam. You may write on any part of the exam; however, only bubbles filled in on the answer sh et will co nt a credit for the multiple choice questions; only answers written in the boxed spaces provided on the exam will count for the essay question. Turn in the exam and the answer sheet at the end of the hour. For rough work, use only the loose sheets provided. Work on loose sheets will not be collected, and will n t be counted. The exam booklet will be returned to you next quiz section. Instructions: Do not begin the exam until you are told t d so; in the me ntime, fill in the information requested below. Practice exam time: 30 minutes, relative o 1 hr. on actual exam PAGE 2 8) Consider the HF+ molecule. Which MO diagram showing 1s(H) and 2pz(F) orbitals best describes the bonding? a) b * b) b * c) b * d) b * e) b * Chem 202 Fall 2008 Hour Exam I 10-08Name: TA: Section: 9) When a drum is hit near the edge, a) The pitch is lower because a wavefunction with higher energy is excited b) The pitch is higher because a wavefunction with more nodes is excit d c) The pitch is lower because the drum behaves like a two dimensional version of a ydrogen atom d) The pitch is higher because the energy associated with the motion of the drum head is higher e) b and d 10) Mountain Dew looks green-yellow because it contains a dye that absorbs all the violet light. In Joules, roughly what is the spacing between the electronic energy levels of the dye across whi h the absorbing electron hops? a) 5.10-50 b) 5.10-19 c 0.0 1 d) 2.1018 e) 1. 048 11) Real chain molecules ar not like perfect box s; the walls are somewhat "soft" b ause the el ctrons can move past the nuclei by 0.5-1 Å. Which of the following properl best describes the pot ntial energy and energy levels of such a box? (The perfect box and levels are s own dotted for ref rence.) a) b) c) d) e) none of these is even close 12) Which of the following statement(s) are correct: a) The Pauli exclusion principle applies only to lectrons, not to protons. b) Two electrons cannot be in the same quantum state, with all quantum numbers the same c) The Heisenberg principle states that quantum part cles occupy an " lbow room" of area h, and the Pauli principle states that these "elbow rooms" can ot overlap d) b and c e) a,b and c Chem 202 Fall 2008 Hour Exam I 10-08 PAGE 1 1) The atomic number of which element is 16? a) oxygen b) potassium c) sulfur d) phosphorus e)none of these b) 2) Which of these is a reasonable potential energy curve for NO? r 0 0 V(r) d) r 0 0 V(r) e) (ii) In question 3, what hybridization best describes the atom shown labeled (labels refer to N,C or O, not any H's that are not shown) H N N H HO H C=CH2 4) Which of the following orderings is in terms of DECREASING at mic radiu ? a) Ca++, K+, Ar, Cl- b) Ar, K+, Ca++, Cl- c) Cl-, Ca++, K+, Ar d) Cl-, Ar, K , a++ e) none 5) Blood plasma contains approximately 7% by mass of the protein albumin. How many mole is protein are contained in 1 liter of blood plasma? (M.W. (albumin) = 69,000 grams/mole; density of blood plasma = 1.06 kg/liter.) a) 9.57.10-4 b) 1.01.10-3 c) 986 d) 992 e) 1.08.10-3 6) What is the elctron configuration of Scandium? a) [Ar] 4s23d1 b) [Ar] 3s23d1 c) [Ar]4s3 d) [Ar]3s22d1 e)[Kr]-4s23d1 7) The laser in a CD player (which reads reflective grooves on the CD surface) ha a wavelen th f 780 nanometers. What is the energy of a single ph ton f om this CD player in Joules? a) 1.7.10-50 b) 1.7.10-45 c) 2.6.10-26 d) 2.6.10-19 e) none of these Note: the actual MOs are distorted from the atomic shapes much more, but this type of sketch is acceptable as an answer on the hour exam. Note: o transition metals on exam! Answer 1: the trajectory looks like a circle or an ellipse: as the spring swings back and forth, the balls slow down when they reach the minimum and maximum values of x; they speed up as the spring swings through the center of its range. So it looks like this: a x p In a multiple choice question, you would be given several shapes. A shape like a x p would not be correct. The particle in a box suddenly flips velocity when it hits the edge of the box, but the balls on a spring gradually slow down as the spring fully extends. Answer 2: It would look like a circle/ellipse of area h: a h x p Just like the classical particle, the quantum particle has to obey energy conservation (within the %E %t " h version of the uncertainty principle we discussed when talking about music!), so momentum has to go down as the spring extends or compresses and the potential energy increases. On a multiple choice exam, misleading answers might look like a 2h x p or a x p h The first answer is wrong because the lowest energy state has area h; the second answer is for a particle in a box with steep walls. Answer 3: 4 electrons, then we need to fill the next energy level. Just kidding about the ‘subspace,’ of course. Answer 4: They are evenly spaced, instead of spreading out or coming closer together, just as the ‘walls’ of the sping potential are neither as steep as the particle in a box, nor as soft as the hydrogen atom. a Spring distance n=1 (also traditionally labeled n=0, with all the others also being 1 less) n=2 n=3 n=4 Some examples of incorrect multiple choice answers would be: a Spring distance n=1 n=2 n=3 n=4 n=0 or a Spring distance n=1 n=2 n=3 n=4 The first of these is wrong because it puts the n=0 particle at the minimum of the potential energy AT REST (p=0, x=0). This is not allowed by the Heisenberg principle. The second of these is wrong because it makes the levels spread out even faster than the particle in a box, so it does not “lie in between.” Answer 4’: If leaves are green (the color complementary to the one being absorbed), then they actually absorb red light (see hints!). The wavelength is therefore 650 nm. Using $#=c and Planck’s law, E=h#=hc/$=6.6.10-34 Js . 3.108 m/s / 650.10-9m ! 3.10-19 J. This would also be the difference between the two energy levels, as the electron absorbs the photon and jumps from the lower level to the higher level. 5. The Fourier principle in this case is %# %t " 1. %# ! 1/%t = 20 s-1 = 20 Hz in the best case. Thus %#/# = 20/880 = 2.3%. Thus the frequency of this note cannot be defined to better than about 2%; no amount of improved measurement will help; this is caused by the inherent linkage of frequency and duration, just as position and momentum are linked in quantum mechanics. 6. a) is the electron density “dot” plot for a 2s orbital. b) is a d-orbital: lobes on opposite sides have the same sign. c) is a pair of px and py orbitals: opposite lobes have different signs. d) a cut through a 2s orbital, multiplied by the radial factor r2. Note that a 2 p orbital also goes up and down, but would be centered at r=0 as follows: a r ! 7. Oxygen has 8 electrons, 6 in the outer shell. Two pair up in the lower energy 2s orbital, leaving 4 in the p orbitals. Of those, the first three are filled into px, py and pz pointing in the same direction, the last one has to double up, leaving two electrons unpaired. The unpaired electrons will point in the same direction to lower the magnetic energy. The spins thus add up to +1 or –1 (depending on whether the unpaired electrons are +1/2, +1/2 or –1/2,-1/2). 8.Chlorine has the higher Zeff, and thus the higher binding strength for additional electrons. Carbon has 6 electrons, 2 inner and 4 valence. Thus +2 out of the +6 nuclear charge is shielded. Of the remainder, three valence electrons shield +1.5 from the 4th one, leaving 6 – 2 – 1.5 = 2.5 of the nuclear charge unscreened; note that the 4th valence electron does not screen itself! Lithium is more electronegative than Cesium; although both have the same nuclear charge Zeff = 1, the orbitals of Cesium are larger, making it easier to remove an electron. 9. Check out the periodic table in the text and make sure you’re not confused by As, Ar, At, Al! 10. Let one of the p’s on C interact with the 1s of H to form a bonding and antibonding orbital. The 2s on C will not do anything. There will be three nonbonding electrons (2 in the 2s, one unpaired in the leftover p), 2 bonding electrons: bond order = 1. For HF, we already have 5 p electrons on C, so the single unpaired one will pair up with 1s of H. BO=2, and all electrons are paired: HF is not a radical. The bonding orbital calculated for CH radical does not look just like a sum of 2p(C) + 1s(H). The reason is thta 1s on hydrogen is closer in energy to 2s (C) than 2p (C). Thus it would be favorable (result in lower energy), if the 2s electron on carbon can be involved in the bonding. The actual bonding orbital thus looks more like a hybrid (20% s, 80%p) of the 2s and 2p on carbon, and then this bonds to the 1s on hydrogen. Note: you won’t get a question this subtle on the exam, but draw out the MO diagram and think about why this makes sense.