Chemistry Department
CHM 1220/1225 Winter 2006
Sample Exam II Answer Key
1. SO2: 18 valence electrons; 8 bonding electrons; 10 nonbonding electrons; all zero formal charges
S
O
O
3. BeF2:16 valence electrons; 4 bonding electrons; 12 nonbonding electrons; all zero formal charges
F
Be
F
+
3. XeF5 : 42 valence electrons; 10 bonding electrons; 32nonbonding electrons; zero formal charge on each F;
+1 on Xe
F
F
+
F
F
Xe
F
––
4. HCO2 :
–
O
–
O
C
H
C
O
H
O
5. δ+ S–O δδ+ Be–F δδ+ Xe–F δδ+ C–O δ- and δ- C–H δ+ (only very slightly polar)
6. SO2 is polar and has a nonzero dipole moment; BeF2 is nonpolar and has a zero dipole moment.
7. Complete the chart below:
CO32–
Arrangement of pairs
Trigonal planar
Molecular Geometry (Shape)
Trigonal planar
ClF4+
Trigonal bipyramidal
See-saw
NH3
Tetrahedral
Trigonal pyramidal
8. Complete the chart below:
CO32–
ClF4+
NH3
9. a.
b.
c.
d.
Hybridization of the
central atom
2
sp
3
sp d
3
sp
5 + 6 = 11 valence electrons: (σ2s)
1
NO: /2(8 – 3) = 2.5
+ 1
NO : /2(8 – 2) = 3
+
NO
2
(σ2s*)2
(π2p)4
Identify each bond as a
σ-bond or π-bond
3 C-O sigma and 1 C-O pi bond
4 Cl-F sigma bonds
3 N-H sigma bonds
(σ2s)2
(π2p*)1
8.
SOLID TYPE
STRUCTURAL UNIT
ATTRACTIVE FORCE
BETWEEN STRUCTURAL
UNITS
cations, anions
Ionic bond
Positive core of metal atom
Metallic bond
Choose one or
two metals
Atoms
Covalent bond
C(diamond),
C(graphite), SiC
Molecules
Intermolecular forces
Ionic
Metallic
Covalent network
Molecular
10. 0º is the melting point/freezing point
100º is the boiling point
EXAMPLE
NaCl
H2O, NH3, etc.