CHE 111- Summer 2016 NAME __Chelsea Dennis __
Dr. Shree Iyengar Homework #7
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This homework covers the major concepts in Chapters 8 and 9, which are very closely related. You should consult the lab manual for relevant information on ‘geometries of molecules.’ There are Chapter notes available for this material under 'Modules' in Canvas.
Learning Outcome for Chapters 8 and 9: When you complete reading the chapter and practicing the end-of-chapter exercises, you are expected the have the following skills as learning outcomes:
* Use appropriate models of chemical bonding to explain the structure of molecules
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1. Explain how the Octet Rule is used in the following situations; you should include relevant electron configurations to support your answer.
a. ionic bond formation between Mg and P
Mg would like to get rid of 2 electrons in the valence shell to obey the Octet rule and P would like to gain 3 electrons to obey the Octet rule. So P will take 2 of Mg electrons to become stable.
b. covalent bond formation in NCl3
N would have to gain 3 electrons to obey the Octet rule and Cl would have to gain 1 electron. So N can pair with 3 Cl to become stable and Cl will be stable as well.
2. Write the abbreviated electron configuration for each of the following ions:
a. Cr3+ b. Telluride ion (Te2—)
[Ar]3d3 [Kr]4d105s25p4
3. Determine the total number of valence electrons for the following molecules (molecular formulas are given in the parenthesis):
a. Niacin (C6H5NO2) - a vitamin, aka vitamin B3
C=4, H=1, N=5, O=6
4x6+5+5+6x2=46
46 Valence electrons
b. 2,5-dimethylfuran (C6H8O) – a compound found in cigarette smoke
4x6+8+6=38
38 Valence electrons
4.. a. Rank the following bonds in order of increasing bond polarity (least to most):
F—C, Br—Br, O—Br, and O—C
__Br-Br__ __O-Br__ __O-C___ ___F-C__
Least polar Most polar
5. Complete the following table with required information (this is similar to lab on geometries of molecules and ions) Total Lewis structure Shape # valence e—
a. HCO2H 18 Trigonal Planar at C Bent at OH
b. N2F2 24 Planar cis
(dinitrogen difluoride)
c. C2N2 (there is a C-C bond) 18 Linear
6. Draw two resonance structures for Bromite ion.
7. a. Explain what is meant by formal charge.
Assuming all electrons in a chemical bond are equally shared, a formal charge is the charge assigned to an atom in a molecule.
b. Assign formal charge to each atom in the Lewis structure of cyanate ion: (Note: the ion has an overall charge of negative one) O: +1
C: 0
N: -2
8. Give the hybridization of the atom shown in bold in the following: (Hint: first draw the Lewis structure for each.)
a. Sulfur in S2F2
Sp
b. the middle Carbon in H2CCCH2
Sp3
9. a. Draw the Lewis structure for each of the following and predict the bond angle in each case:
a. SCl2 b. BeCl2
b. Would you expect either of the above two compounds to be a polar molecule? What criteria do you use to determine the overall polarity of each?
SCl2 would be considered a polar molecule because it contains 2 pairs of electrons and 2 polar bonds. BeCl2 has 1.5 polar bonds so it would be considered polar as well.
10. Consult page 330 in the textbook for the structure of TNT that shows all the atoms and all the bonds.
a) How many sigma and pi bonds does this compound have?
Sigma: 21
Pi bonds: 6
b) What is the hybridization of C atom that is outside the ring?
Sp3
c) What is the hybridization of N atom (all three N’s have the same hybridization)? Sp2 