Exam 1: Physics - Quantum Mechanics and Atomic Structure - Prof. Sara J. Sutcliffe, Exams of Chemistry

Download Exam 1: Physics - Quantum Mechanics and Atomic Structure - Prof. Sara J. Sutcliffe and more Exams Chemistry in PDF only on Docsity! Version 145 – Exam 1 – sutcliffe – (51310) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. This exam is ONLY for students in the 2- 3pm AFTERNOON SECTION. 2-3pm51310 AFTERNOON class only Sutcliffe 001 10.0 points Radio stationKLBJ broadcasts at a frequency of 93.7× 106 s−1. Determine the length of the waves that corresponds to this frequency. 1. 93.7 m 2. 2× 10−8 m 3. 2 nm 4. 3.20 nm 5. 3.20 m correct Explanation: 002 10.0 points What is the de Broglie wavelength of Schrodinger’s cat, Albert, running to his food bowl. Albert has a mass of 5200 g and is running at 1.6 m/s. 1. 7.964× 10−35 m correct 2. 4.978× 10−35 m 3. 5.513× 10−33 m 4. 7.964× 10−38 m Explanation: λ = h p = h m · v = 6.626× 10−34 kg·m 2 s (5.2 kg) (1.6 m/s) = 7.96394× 10−35 m 003 10.0 points The photoelectric effect shows that for ametal surface irradiated with photons, if no elec- trons are released from the surface, then in order to release photoelectrons... 1. the wavelength of the photons must be increased. 2. the frequency of the photons must be decreased. 3. the frequency of the photons must be increased. correct 4. the temperature of the surface must be increased. 5. the photon intensity must be decreased. 6. the work function of the surface must be increased. Explanation: When electromagnetic radiation (light) of sufficient minimum energy strikes a metal cathode, electrons are knocked off its sur- face, travel to an anode, and form a current through a circuit. Two important observations were: 1) Electrons can be ejected only if the light is sufficiently energetic. Electron ejection is independent of time or intensity. The mini- mum energy varies by element. 2) The current increases with increasing intensity and is independent of color. Therefore, light is made up of photons, each having a particular amount of energy that can be transferred to an electron during a colli- sion. If the energy is equal to or greater than the amount needed to liberate the electron, it can escape to join the photoelectric current. Intensity is the number of photons hitting a surface per unit time. Version 145 – Exam 1 – sutcliffe – (51310) 2 004 10.0 points What is the formula for copper(I) sulfite? 1. CuSO3 2. Cu2SO4 3. CuSO4 4. Cu2SO3 correct 5. Cu2S 6. CuS Explanation: The copper(I) ion is Cu+; the sulfite ion is SO23 −. Two Cu+ are needed to balance the charge on each SO23 −, so the formula is Cu2SO3. 005 10.0 points In a one-dimensional particle in a box, the zero-point energy corresponds to 1. n = 1. correct 2. Ψ2 = 0. 3. n = 0. 4. a node. 5. a quantum state where the Uncertainty Principle is not valid. Explanation: Zero point energy refers to the idea that even in the lowest possible energy level for the one-dimensional particle in a box (n = 1), the energy will not be zero; it will be E = h2 8mL2 . 006 10.0 points Consider the electron filling diagram 3p ↑↓ ↑ 3s ↑ 2p ↑↓ ↑↓ ↑↓ 2s ↑↓ 1s ↑↓ for a ground state atom. Which of the follow- ing does it violate? I) The Aufbau principle II) Hund’s rule III) The Pauli exclusion principle 1. I, III 2. I only 3. I, II, III 4. II only 5. II, III 6. I, II correct 7. III only Explanation: Aufbau’s principle says you must fill the orbitals in order from lowest energy to high- est. Putting electrons in the 3p orbitals before filling the 3s orbital violates that. Hund’s rule says that orbitals in the same subshell must each have an unpaired electron before any of them can have a pair. This is violated in the 3p subshell. The Pauli exclusion principle says that no two electrons can have the same four quantum numbers, which the given configuration does not violate. 007 10.0 points Which of the following is an alkaline earth metal? 1. Sc 2. Fe Version 145 – Exam 1 – sutcliffe – (51310) 5 to shorter wavelengths as the temperature of the blackbody increases. CORRECT 4. The emission from a blackbody consists of a series of discrete spectral lines, the colors of which are unique to the type of blackbody used. Explanation: A blackbody’s radiation emission curve is broad, lopsided and has a peak which shifts to shorter wavelengths as the temperature of the blackboady increases. Theoreticians tried to model this using classical mechanics and never could get their models to behave be- cuase they predicted vast amounts of UV, gamma, etc. being produced by a blackbody above absolute zero - the ”UV Catastrophe”. A plain old incandescent lightbulb with a dim- mer switch can be used to reproduce the emis- sion curves of a blackbody - and even vary its temperature by changing the current with the dimmer switch. 017 10.0 points What is the formula for phosphorous pentaflu- oride? 1. PF5 correct 2. PF 3. P7F 4. PF9 5. K5F 6. P5F 7. KF5 8. PF7 Explanation: This compound’s name suggests 1 phos- phorus atom for every 5 fluorine atoms. The symbol for phosphorus is P, and that for flu- orine is F. The less electronegative atom P is written first in the formula. 018 10.0 points A given atomic orbital has a total of two nodal planes. What type of orbital is this? 1. g 2. f 3. s 4. d correct 5. p Explanation: A node is a point, a plane or a three dimen- sional region of space where the sign of the wavefunction changes from positive to neg- ative (or negative to positive), so it equals zero. The lowest energy orbital of each type will have no three dimensional nodes but dif- fering numbers of nodal planes: 1s – no nodal planes 2p – one nodal plane (two opposing lobes of different signs) 3d – two nodal planes (four opposing lobes of two different signs) 4f – three nodal planes (six opposing lobes of two different signs) (One orbital has only one nodal plane and one conical node for both 3d and 4f .) If we go to the next higher value of n for the same type of orbital we would add a spherical (radial) node but the number of nodal planes would remain the same. 019 10.0 points Which of the following sets of quantum numbers are valid, i.e. don’t violate any boundary conditions? I) n = 3, ℓ = 2, mℓ = −2, ms = + 1 2 II) n = 9, ℓ = 5, mℓ = 6, ms = + 1 2 III) n = 2, ℓ = 1, mℓ = 0, ms = +1 IV) n = 2, ℓ = 0, mℓ = 0, ms = + 1 2 Version 145 – Exam 1 – sutcliffe – (51310) 6 1. III only 2. IV only 3. I only 4. I, III, IV 5. I, II, IV 6. I, IV correct 7. II only 8. II, III Explanation: Set II and III are invalid. For II, mell = 6 is disallowed because ℓ = 5. For III, ms = +1 is disallowed because ms may only be + 1 2 or − 1 2 . 020 10.0 points Which of the following has the same electron configuration as Ca2+ ? 1. S2− correct 2. Ne 3. Ca 4. Mg2+ 5. F− Explanation: We are looking for the atom or ion that is isoelectronic to Ca2+. (Isoelectronic means to have the same number of electrons; con- sequently the same electron configuration.) The net +2 charge indicates that Ca2+ has two more protons than electrons. Since cal- cium always has 20 protons, Ca2+ must have 18 electrons, so we need an answer choice with 18 electrons. A neutral calcium atom has 20 electrons. The +2 charge on Mg2+ indicates that the magnesium atom has two more protons than electrons, so it has 10 electrons total. Ne has 10 electrons. The −1 charge on F1− indicates that the ion has one more electron than proton, so F1− has a total of 10 electrons. The −2 charge on S2− indicates that the ion has two more electrons than protons. S2− has 16 protons and therefore must have 18 electrons. S2− is isoelectronic with Ca2+. 021 10.0 points You need 50.0 g of milk for a cookie recipe, but you don’t have a scale. You do know that milk has a density of 1.10 g/cm3. Knowing that 1 cm3 = 1 mL, how much milk should you should use for this cookie recipe? 1. 48.90 mL 2. 22.0 mL 3. 51.1 mL 4. 45.5 mL correct 5. 55.0 mL Explanation: (50 g) · cm3 1.1 g · 1 mL cm3 = 45.4545 mL 022 10.0 points Compared to a 280 nm photon, a 320 nm photon has 1. longer wavelength, lower frequency, lower energy. correct 2. longer wavelength, lower frequency, higher energy. 3. longer wavelength, higher frequency, higher energy. 4. shorter wavelength, higher frequency, lower energy. 5. shorter wavelength, lower frequency, higher energy. Version 145 – Exam 1 – sutcliffe – (51310) 7 6. shorter wavelength, lower frequency, lower energy. Explanation: 023 10.0 points A comparison of the electron configurations of zirconium (Zr) and Molybdenum (Mo) in- dicates that 1. Mo has three more d electrons and one less s electron than Zr. correct 2. Mo has two more d electron and one less s electron than Zr. 3. Mo has one more d electron and one more s electron than Zr. 4.Mo has two more d electrons and the same number of s electrons as Zr. 5. Mo has three more d electron and the same number of s electrons as Zr. Explanation: The electron configuration for Zr is [Kr] 5s24d2, whereas the electron configuration for Mo is [Ar] 5s14d5. 024 10.0 points Which of the following is the molecular for- mula for pentane? 1. C6H14 2. C4H10 3. C7H16 4. C5H12 correct 5. C3H8 Explanation: 025 10.0 points Consider a Bohr atom with the following en- ergies for the first three energy levels: 1st energy level : −5× 10−18 J 2nd energy level : −6× 10−19 J 3rd energy level : −2× 10−19 J A photon with energy = 4.4×10−18 J interacts with the atom. What might happen as a result of this interaction? 1. None of the transitions listed would oc- cur. 2. An electron could transition from the 1st to 2nd energy level. correct 3. An electron could transition from the 1st to 3rd energy level. 4. An electron could transition from the 2nd to 3rd energy level. Explanation: 026 10.0 points An electron in a hydrogen atom moves from the n = 2 to n = 5 level. What is the wave- length of the photon that corresponds to this transition and is the photon emitted or ab- sorbed during this process? 1. 1875 nm; emitted 2. 434 nm; absorbed correct 3. 276 nm; absorbed 4. 1875 nm; absorbed 5. 276 nm; emitted 6. 434 nm; emitted Explanation: 027 10.0 points In attempting to explain the line spectrum of hydrogen, Bohr suggested that the energy of electrons in atoms is 1. continuous. 2. infinite.