Name
Section
Rec TA
Ch 1a, Problem Set Five
Due Friday, Oct. 30, 2015
at 4 PM in the Drop Box
Side 1 of 2
Problems 1 and 2 are designated (() as ‘no collaboration’ problems.
( 1. (15 Points) Out of each pair, which neutral element has the lower ionization energy?
Explain each answer with screening and/or electronic configurations for full credit.
a. (5 points) Na , Mg
b. (5 points) Zn , Ge
c. (5 points) Mg , Ne
( 2. (10 Points) Making covalent bonds to silicon surfaces has important implications for the
silicon device industry.
a. (5 points) Calculate the difference in Pauling electronegativity (page 56, Gray) for
each Si-R bond listed below:
Si-Cl, Si-OH, Si-H, Si-CH3, Si-SiH3, Si-F
b. (5 points) Rank each bond from the most ionic to most covalent.
3. (25 Points; 5 each) For each of the following molecules, draw a Lewis dot structure. For
full credit you must include all lone pairs and formal charges. Show any significant
resonance structures. (For background on resonance structures, see Oxtoby, Gillis &
Campion 6th edition on p. 89, or Gray on p. 64.)
a. [OCHCH2]b. NO2 (hint: N is the central atom)
c. O3 (hint: not a triangle)
SOF6 (hint: one F attached to O)
e. SO3 (hint: there are 3 possible
d.
formal charges for S in this case)
4. (5 Points) When drawing Lewis dot structures, many students think in only two
dimensions, even though molecules exist in three dimensions. Several phosphorus
compounds show interesting architectures for which Lewis dot structures cannot be
drawn if one is constrained to two-dimensional thinking.
Draw the structure of P4. The 3D geometry must be clear from your drawing.
Don’t consider resonance structures or formal charges.
Name
Section
Rec TA
Side 2 of 2
Ch 1a, Problem Set Five
Due Friday, October 30, 2015
at 4 PM in the Drop Box
5. (45 Points) In lecture, you saw the following chart of oxoacids of the form –X-O-H.
For each pair, identify which oxoacid is a stronger acid and then briefly explain your
answer. Be sure to include all relevant factors that influence acidity. In some cases,
you may need to use structures to justify your explanation.
a.
b.
c.
d.
(6 points) H3AsO4 vs. H3PO4
(6 points) H2SO4 vs. HSO4(12 points) HClO2 vs. HClO4 (Hint: you must draw resonance structures)
(6 points) HClO vs. HCO3-
Based on resonance arguments, you might expect H2CO3 to be a much stronger acid than
H3PO3. It is in fact only a slightly better acid.
e. (8 points) Using resonance diagrams, show why, at first glance, we would expect
H2CO3 to be a much better acid than H3PO3. (At first glance we assume the
molecule has the form, P(OH)3.)
f. (7 points) Propose a reasonable Lewis dot structure for H3PO3 that is consistent
with the measured relative acidities. Explain why. (Hint: none of the rules
regarding resonance stabilization of products are being broken here!)