Written Assignment 9: Chemical Bonding
Answer all assigned questions and problems, and show all work.
1. Use the second member of each group from Group IA to Group 7A to show that the number of valence electrons on an atom of the element is the same as its group number.
Li has 1 valence electron
Cl has 7 valence electrons
(Reference: Chang 9.2)
2. Explain the following: (3 points)
a. ionic bond=electrostatic force that holds ions together in an ionic compound.
b. nonpolar covalent bond=electrons are shared equally between the two atoms.
c. polar covalent bond= the electrons spend more time in the vicinity of one atom than the other.
3. Specify which compound in the following pairs of ionic compounds has the higher lattice energy: Explain your choice. (6 points)
a. KCl or MgO=MgO
b. LiF or LiBr=LiBr
c. Mg3N2 or NaCl=NaCl
(Reference: Chang 9.23)
4. Compare the properties of ionic compounds and covalent compounds. (6 points)
Electronegativity is a property of atoms, not bonds. An ionic bond is formed between elements with very different electronegativities, a covalent bond between atoms with similar electronegativities.
(Reference: Chang 9.32)
5. Four atoms are arbitrarily labeled D, E, F, and G. Their electronegativities are as follows: D = 3.8, E = 3.3, F = 2.8, and G = 1.3. If the atoms of these elements form the molecules DE, DG, EG, and DF, how would you arrange these molecules in order of increasing covalent bond character? (4 points)
(Reference: Chang 9.37)
6. Classify the following bonds as ionic, polar covalent, or nonpolar covalent, and
give your reasons: (4 points)
a. the CC bond in H3CCH3- Covalent
b. in KI the KI bond- Ionic
c. the NB bond in H3NBCl3– Polar Covalent
d. the CF bond in CF4– Polar Covalent
(Reference: Chang 9.39)
7. Write the correct Lewis structures for the following compounds (relative positions of atoms are shown correctly).(21 points)
a. H C N
b. H C C H
c. O Sn O
d. F F
e. H O F
g. F F
(Reference: Chang 9.47)
8. Classify the following substances as ionic compounds or covalent compounds containing discrete molecules: CH4, KF, CO, SiCl4, BaCl2.(5 points)
CH4=Covalent KF=Ionic CO=Covalent SiCl4=Covalent BaCl2=Ionic
(Reference: Chang 9.73)
9. Predict the geometries of the following species using the VSEPR method: (a) PCl3,
(b) CHCl3, (c) SiH4, (d)TeCl4. (12 points)
a. 1 lp AX3E trigonal pyramidal
b. 0 lp AX4 tetrahedral
c. 0 lp AX4 regular tetrahedral
d. 1 lp AX4E a see-saw structure
(Reference: Chang 10.7)