시험 17 4월 2016, 문제 PDF

Preview

Summary

inorganic chemistry midterm exam...

Description

Inorganic Chemistry I (CHM2401) Mid-term Exam (16 questions, 120 points)

Apr 22, 2016

답안을 문제 순서대로 작성하고, 계산 문제의 경우 푸는 과정을 반드시 쓰시오 쓰시오! 답만 쓰면 점수가 없습니다. 서술식의 경우 핵심적인 내용이 모두 들어가야 주어진 점수를 모두 받을 수 있습니 습니다 다.

H

He

Li

Be

B

C

N

O

F

Ne

Na

Mg

Al

Si

P

S

Cl

Ar

Se

Br

Kr

I

Xe

K

Ca Sc

Ti

V

Rb

Sr

39Y

Zr

Cs

Ba

57La

Hf

Fr Ra

89Ac

Cr

Mn Fe

Co

Ni

Cu Zn

Ga

Ge As

Nb

Mo Tc Ru

Rh

Pd

Ag Cd

In

Sn Sb Te

Ta

W

Re Os

Ir

Pt

Au Hg

Tl

Pb

Bi

Po

At

Rn

58Ce

Pr

Nd Pm Sm Eu Gd Tb

Dy Ho

Er

Tm Yb

Lu

90Th

Pa

Es Fm Md No

Lr

U

Np

Pu Am Cm Bk

Cf

1. (3 points × 3 = 9 points) For the 5s and 4dxz hydrogen-like atomic orbitals, sketch the following: (a) The radial function R (x axis = r/a0). (b) The radial probability function a0r2R2 (x axis = r/a0). (c) Contour maps of electron density (xz plane).

2. (4 points × 2 = 8 points) (a) Determine the most favorable arrangement of 2p electrons in 2p orbitals of an oxygen atom, and explain why the arrangement is most favorable with Pauli exclusion principle and Hunt’s rule of maximum multiplicity. (b) Explain why the arrangement is most favorable with the Coulombic and exchange energies of the arrangement comparing the energies with those of the other possible arrangement, (↑↓ ↑↓

).

3. (6 points) According to Slater’s rules, a 3d electron of nickel has a higher effective nuclear charge than a 4s electron. Is the same true for early first-row transition metals? Using Slater’s rules, calculate S and Z* for 4s and 3d electrons of Sc and Ti, and comment on the similarities or differences with Ni.

1

4. (4 points) The graph of ionization energy versus atomic number for the elements Na through Ar shows maxima at Mg and P and minima at Al and S. Explain these maxima and minima.

5. (2 points × 3 = 6 points) Select the best choice, and briefly indicate the reason for each choice: (a) Smallest radius: Sc, Ti, V. (b) Greatest volume: S2–, Se2–, Te2–. (c) Highest electron affinity: O, F, Ne.

6. (5 points) Three isomers having the formula N2CO are known: ONCN (nitrosyl cyanide), ONNC (nitrosyl isocyanide), and NOCN (isonitrosyl cyanide). Draw the most important resonance structures of these isomers, and determine the formal charges. Which isomer do you predict to be the most stable (lowest energy) form?

7. (2 points × 5 = 10 points) Give Lewis dot structures , sketch and explain the shapes of the following: (a) SOF4, (b) ICl3, (c) XeO2F4, (d) PF3(CH3)2, (e) PF3(CF3)2.

8. (2 points × 2 = 4 points) X-ray crystal structures of ClF3O and BrF3O have been determined. (a) Would you expect the lone pair on the central halogen to be axial or equatorial in these molecules? Why? (b) Which molecule would you predict to have the smaller Fequatorial-central atom-oxygen angle? Explain your reasoning.

9. (3 points + 2 points = 5 points) Using (a) the LCP approach and (b) the polarity of these molecules, provide a rationale for HOF having the smallest bond angle in this set.

2

10. (4 points + 2 points + 2 points = 8 points) Provide explanations for the following: (a) Of the compounds mercury(II) cyanate, Hg(OCN)2, and mercury(II) fulminate, Hg(CNO)2, one is highly explosive, and the other is not. (b) The boiling points of the noble gases increase with atomic number. (c) Carbon monoxide has a greater bond-dissociation energy (1072 kJ/mol) than molecular nitrogen (945 kJ/mol).

11. (1.5 points × 6 = 9 points) Determine the point groups for (a) HCN, (b) acetylene, (c)

(d)

(e)

(f)

12. (3 points × 3 = 9 points) List all the symmetry operations for each of the molecules, classify the symmetry operations into classes, and finally determine the point group. (a) NH3, (b) ethylene, (c) staggered ethane.

13. (2 points + 3 points × 3 = 11 points) For PF5, which has D3h symmetry: (a) List all the symmetry operations for this molecule. (b) Write a set of transformation matrices that describe the effect of each symmetry operation in the D3h group on a set of coordinates x, y, z for a point. (Hint: Your answer should consist of six 3 X 3 transformation matrices. New coordinates (x’, y’) of a point (x, y) after rotation of θ: x’ = x cos θ – y sin θ, y’ = x sin θ + y cos θ) (c) Using the terms along the diagonal, obtain as many irreducible representations as possible from the transformation matrices. (You should be able to obtain two irreducible representations in this way.) (d) Except the two-dimensional irreducible representation obtained from (c) D3h group has another twodimensional irreducible representation with  (C3 or C32) of –1. Using the properties of characters of irreducible representations in point groups, make a D3h character table except the matching functions in the right part of the table.

3

14. (1 point + 2 points × 2 + 3 points = 8 points) Using the D2d character table:

(a) Determine the order of the group. (b) Verify that the E irreducible representation is orthogonal to each of the other irreducible representations. (c) For each of the irreducible representations, verify that the sum of the squares of the characters equals the order of the group. (d) Reduce the following representations to their component irreducible representations:

15. (3 points × 4 = 12 points) XeOF4 has one of the more interesting structures among noble gas compounds. On the basis of its C4v symmetry:

(a) Obtain a reducible representation based on all the motions of the atoms in XeOF4. (b) Reduce the representation to its component irreducible representations. (c) Classify these representations, indicating which are for translational, rotational, and vibrational motion. (d) Obtain a representation based on the xenon-oxygen bond and determine the corresponding irreducible representation. Is the xenon-oxygen stretching vibration IR active?

16. (3 points × 2 = 6 points) For 1,1,2,2-tetraiododisilane, which has C2h symmetry:

(a) Predict the number of IR-active Si-I stretching vibrations. (b) Predict the number of Raman-active Si-I stretching vibrations.

4

Inorganic Chemistry I (CHM2401) Final Exam (17 questions, 150 points)

Jun 17, 2016

답안을 문제 순서대로 작성하고, 계산 문제의 경우 푸는 과정을 반드시 쓰시오 쓰시오! 답만 쓰면 점수가 없습니다. 서술식의 경우 핵심적인 내용이 모두 들어가야 주어진 점수를 모두 받을 수 있습니 습니다 다.

H Li

He Be

B

C

N

O

F

Ne

Na Mg

Al

Si

P

S

Cl

Ar

As

Se

Br

Kr

I

Xe

K

Ca

Sc

Ti

V

Rb

Sr

39Y

Zr

Cs

Ba

57La

Hf

Fr Ra

89Ac

Cr

Mn Fe

Co

Ni

Cu

Nb

Mo Tc Ru

Rh

Pd

Ag Cd

In

Sn Sb Te

Ta

W

Re Os

Ir

Pt

Au Hg

Tl

Pb

Bi

Po

At

Rn

58Ce

Pr

Nd Pm Sm Eu Gd Tb

Dy Ho

Er

Tm Yb

Lu

90Th

Pa

Es Fm Md No

Lr

U

Np

Zn

Pu Am Cm Bk

Ga Ge

Cf

1. (6 points) According to Slater’s rules, a 3d electron of nickel has a higher effective nuclear charge than a 4s electron. Is the same true for early first-row transition metals? Using Slater’s rules, calculate S and Z* for 4s and 3d electrons of Sc and Ti, and comment on the similarities or differences with Ni.

2. (2 points × 2 = 4 points) X-ray crystal structures of ClF3O and BrF3O have been determined. (a) Would you expect the lone pair on the central halogen to be axial or equatorial in these molecules? Why? (b) Which molecule would you predict to have the smaller Fequatorial-central atom-oxygen angle? Explain your reasoning.

3. (3 points) List all the symmetry operations for staggered ethane, classify the symmetry operations into classes, and finally determine the point group.

4. (2 points + 3 points × 3 = 11 points) For PF5, which has D3h symmetry: (a) List all the symmetry operations for this molecule. (b) Write a set of transformation matrices that describe the effect of each symmetry operation in the D3h group on a set of coordinates x, y, z for a point. (Hint: Your answer should consist of six 3 X 3 transformation matrices. New coordinates (x’, y’) of a point (x, y) after rotation of θ: x’ = x cos θ – y sin θ, y’ = x sin θ + y cos θ) (c) Using the terms along the diagonal, obtain as many irreducible representations as possible from the transformation matrices. (You should be able to obtain two irreducible representations in this way.)

5

(d) Except the two-dimensional irreducible representation obtained from (c) D3h group has another twodimensional irreducible representation with  (C3 or C32) of –1. Using the properties of characters of irreducible representations in point groups, make a D3h character table except the matching functions in the right part of the table. 5. (3 points × 2 = 6 points) For 1,1,2,2-tetraiododisilane, which has C2h symmetry:

(a) Predict the number of IR-active Si-I stretching vibrations. (b) Predict the number of Raman-active Si-I stretching vibrations.

6. (5 points + 2 points × 3 = 11 points) The hypofluorite ion, OF–, can be observed only with difficulty. (a) Prepare a molecular orbital energy level diagram (formed with 2s and 2p atomic orbitals) for this ion. (b) How does your diagram illustrate the difference in electronegativity between O and F? (c) What is the bond order, and how many unpared electrons are in this ion? (d) What is the most likely position for adding H + to the OF– ion? Explain your choice.

7. (8 points + 2 points = 10 points) Methylene, CH2, plays an important role in many reactions. One possible structure of methylene is linear. (a) Construct a molecular orbital energy-level diagram for this species. Include sketches of the group orbitals, and indicate how they interact with the appropriate orbitals of carbon. (b) Would you expect linear methylene to be diamagnetic or paramagnetic? Explain your choice.

8. (6 points × 3 + 3 points + 8 points = 29 points) (a) Using the D2h point group of CO2, construct reducible representations for the combination of 2s, 2px, 2py, and 2pz orbitals on the O atoms, respectively and reduce the representations to their irreducible representations. (b) Draw the group orbitals for CO2 composed of 2s, 2px, 2py, and 2pz orbitals on the O atoms, respectively and match the group orbitals with the labels of the irreducible representations obtained in (a). (c) Illustrate all the interactions between the atomic orbitals of central carbon (2s, 2px, 2py, and 2pz orbitals) and the group orbitals found in (b) with the same symmetries. (d) Explain why the group orbitals formed by adding and subtracting the oxygen 2s orbitals are essentially nonbonding in the molecular orbitals of CO2. (e) Use the projection operator method to derive normalized SALCs that define the group orbitals for CO2 based on the oxygen 2s ( (O2s(A)) and (O2s(B))) and 2py ((O2py(A)) and (O2py(B))) orbitals, respectively (Hint: Use the normalizing factor for the determination of coefficients.).

6

9. (2 points × 3 = 6 points) (a) Write a function defining H0 that can be used to represent superacid acidity. (b) HF has H0 = –11.0. How does the addition of 4% SbF5 affect the H0 value of the resulting solution? (c) Write a chemical equation for reversible processes that can explain why SbF5 should have such a strong effect and why the resulting solution is so strongly acidic that it can protonate alkenes. (CH3)2C=CH2 + H+  (CH 3)3C+

10. (3 points × 4 = 12 points) Correlation of gas-phase and aqueous-solution basicity data is instructive. The figure below shows a graph of gas-phase basicity vs. pK a of conjugate acids in water for some Brønsted– Lowry bases.

(a) Arrange the bases in the order of increasing basicity in gas-phase and water, respectively. Qualitatively, how well do these gas phase and solution data correlate? Explain. (b) Rationalize the positions of the ethers on the graph relative to the alcohols and water. (c) Qualitatively, how welI do the gas phase and solution data correlate for the two ethers and the two alcohols? Are these trends the result of inductive or steric effects? Explain. (d) Rationalize the seemingly paradoxical location of water in your graph relative to the other bases.

7

11. (3 points + 5 points = 8 points) The absorption spectra of solutions containing Br2 are solvent dependent. When elemental bromine is dissolved in nonpolar solvents such as hexane, a single absorption band in the visible spectrum is observed near 500 nm. When Br2 is dissolved in methanol, however, this absorption band shifts and a new band is formed. (a) Account for the appearance of the new band. (b) Illustrate the interactions between the appropriate orbitals of Br2 and methanol and expect whether the 500 nm band is likely to shift to a longer or shorter wavelength in methanol. 12. (4 points) The most common source of mercury is cinnabar (HgS), whereas Zn and Cd in the same group occur as sulfide, carbonate, silicate, and oxide. Why?

13. (4 points × 2 = 8 points) (a) What percent of the total volume is occupied by spheres in a body-centered cube in which all atoms are identical? (b) LiBr has a density of 3.464 g/cm3 and the NaCl crystal s tructure. Calculate the interionic distance. Atomic weights of Li and Br are 6.941 u and 79.904 u, respectively.

14. (5 points × 3 = 15 points) Answer the questions. (a) Draw the band structures of a metal with overlapping bands and a p-type semiconductor and represent Fermi levels in the structures. (b) Suggest two different types of applications of a p-n junction and explain the fundamentals of operating the functions. (c) What is the Meissner effect of a superconductor? Describe the type of superconductors that can be used to demonstrate the effect. Suggest an application of the effect.

15. (5 points) A series of ZnSe quantum dots was prepared of a range of sizes, with diameters from approximately 1.5 to 4.5 nm, and the photoluminescence emission spectra were recorded. Were the lowest energy emission bands produced by the largest or smallest quantum dots? Explain your choice with the quantum confinement effect of quantum dots. 16. (2 points) Determine the formulas of the following silicate.

17. (6 points + 4 points = 10 points) (a) Construct a Frost diagram (x axis = oxidation state, y axis = –nE) from the Latimer diagram below for nitrogen in acidic solution:

(b) Deduce the reduction potential for N2O  NH3OH+.

8...