CH141f Study Guide - Midterm Guide: Antibonding Molecular Orbital, Atomic Radius, Isoelectronicity

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11 Oct 2018
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CH141 – Practice Exam 3 Page 1 of 7
Name: __Answer Key____________
Part I. Multiple Choice:
1. Which of the following pairs of atoms/ions is isoelectronic?
__ A. O–2, S–2
__ B. Na, Na+1
X_ C. Br–1, Kr
__ D. Cu, Zn
__ E. none of these
2. Which of the following quantum number sets describes a 4f orbital?
__ A. n=2, l=0, ml= 0
__ B. n=3, l=1, ml= -1
__ C. n=3, l=2, ml= -1
__ D. n=4, l=2, ml= +1
X_ E. n=4, l=3, ml= +2
3. Which element below has the largest atomic radius?
__ A. S
X_ B. P
__ C. N
__ D. B
__ E. F
4. Which element below has the highest electronegativity?
__ A. C
__ B. P
X _ C. N
__ D. B
__ E. Be
5. Order the elements S, Cl, and F in terms of increasing atomic radii.
__ A. S, Cl, F
__ B. Cl, F, S
__ C. F, S, Cl
X_ D. F, Cl, S
__ E. S, F, Cl
6. Which of the following statements is true?
__ A. Electrons are never found in an antibonding MO.
__ B. All antibonding MOs are higher in energy than the atomic orbitals of which they are composed.
__ C. Antibonding MOs have electron density mainly outside the space between the two nuclei.
__ D. None of the above is true.
X_ E. Two of the above statements are true. (B and C)
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CH141 – Practice Exam 3 Page 3 of 7
13. In one sentence, clearly explain why CO has a small bond dipole (polar compound) and the oxygen
has a partial positive charge. You can draw a picture to support your answer.
Although oxygen is more electronegative than carbon, CO has a +1 formal charge on O and a -1
formal charge on C, which causes a slight bond dipole toward the C.
C O
–1 +1
14. In one sentence, clearly explain why MgO has a much higher lattice energy than NaF.
It takes more energy to separate ions with larger charges due to increased coulombic attraction.
15. For laughing gas, N2O
a) Draw a valid Lewis structure below (connectivity N–N–O). Assign formal charges to all atoms.
N N O
1 +1
b) Draw two additional resonance structures of the structure you drew in part (a). Assign formal charges
to all atoms.
N N O ONN
+1 –1 +1+1
–2
c) Circle the single structure above (from the three structures in parts (a) and (b)) that most closely
represents the true structure of N2O and briefly explain your choice.
Formal charges are minimized and the -1 formal charge is on the most electronegative atom.
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