HOMEWORK for UNIT 3. Molecules
1. a. Define ionization energy and describe the general trend in ionization energy across a period and
down a group.
b. Which has a larger ionization energy:
i. Rb or Li
ii. S or Cl
iii. F or Br
iv. Ba or Cs
2. a. What happens to ionization energy as you remove each successive electron?
b. When does it suddenly take much more energy to remove an electron? Why?
3. a. Define valence electrons.
b. How many valence electrons are in an atom of carbon (C)?
c. Write the Lewis dot symbols for iodine (I), strontium (Sr), and arsenic (As).
4. Complete these sentences:
a. The octet rule states that ______________________ .
b. Octet rule predicts that an atom of oxygen will try to _____
_____ electrons when forming a
compound.
gain, lose 1, 2, 3, 4
c. Octet rule predicts that an atom of potassium will try to _____
_____ electrons when
forming a compound.
gain, lose 1, 2, 3, 4
5. Predict the charge of the ion formed by each of these elements.
a. Sr
b. I
c. S
d. Cs
6. Which is larger:
a. O or O2–
b. Na or Na1+
c. Cl1– or Cl
d. Ba2+ or Ba
7. Use Lewis dot symbols to show the formation of each of these salts:
a. KI
b. BaS
c. Na2O
d. MgCl2
8. a. What is a covalent bond?
b. what is the difference between a single covalent bond and a double covalent bond?
9. Write a Lewis structure for each of these:
a. H2S
b. CO2
c. ClO21–
d. POF3
10. Write a Lewis structure for each of these:
a. HClO
b. N31–
c. PCl3
d. CH3OH
e. CH3Br
e. C2N2
f. C2H4
f. SOF2
11. Describe and draw the “sea of electrons” model for bonding in metals (look at Figure 7.12, pg 201 in
your text), and describe how this model explains these properties of metals:
a. ability to conduct electricity
b. malleability
12. Predict the type of bonding you expect in each of these substances, and describe how you know:
a. BaCl2 b. SO2 c. Zn d. CH4 e. bronze (Cu + Sn) f. KI g. Al2O3 h. AsF3
13. Is H a metal or a nonmetal? What type of bonding do you expect for H?
Bond polarity
12. a. What is electronegativity?
b. What does it mean to say that a bond is polar?
13. For each bond, show its electronegativity difference (∆EN), indicate the direction of polarity (if any)
with an arrow, and classify the bond as nonpolar covalent, polar covalent, or ionic using the criteria in
Table 8.3 on pg 238 in your text. The chart of electronegativity values is on pg 177 in your text.
a. H–Cl
b. F–F
c. Mg–O
d. H–O
e. C–Cl
f. H–As
g. Na–Cl
Shapes of molecules & molecular polarity
14. Predict the shape of each molecule in problems 10 & 11. If there is more than one central atom,
predict the shape around each central atom.
15. What does it mean to say that a molecule is polar, or has a dipole?
16. Predict whether each structure in problems 10 & 11 is polar or nonpolar, and justify your choice.
7. Why do we describe each of the chemical formulas above as a “formula unit” instead of a molecule?
8. List three characteristic behaviors that you expect for a salt.