Department of Chemistry
CHM 1220/1225 – Exam II Form A
1. Write the best Lewis formula for BCl3.
(a) the number of valence electrons:
3 + 3(7) = 24
(a) the number of bonding electrons:
6
(a) the number of nonbonding electrons 18
(a) the formal charge of each atom
zero
(a) resonance structures if they are needed
Cl
Cl
B
Cl
2–
2. Write the best Lewis formula for SO3 .
(a) the number of valence electrons:
(a) the number of bonding electrons:
(a) the number of nonbonding electrons
(a) the formal charge of each atom
1(6) + 3(6) + 2 = 26
8
18
zero on S and double bonded O; –1 on single bonded O’s
2–
O
2–
S
O
O
O
2–
O
O
S
S
O
O
3. Write the best Lewis formula for SeF4.
(a) the number of valence electrons:
(a) the number of bonding electrons:
(a) the number of nonbonding electrons
(a) the formal charge of each atom
4. Write the best Lewis formula for C2F2
(a)
(b)
(b)
(b)
the number of valence electrons:
the number of bonding electrons:
the number of nonbonding electrons
the formal charge of each atom
F
1(6) + 4(7) = 34
8
26
zero
2(4) + 2(7) = 22
10
12
zero
O
F
F
C
Se
F
F
C
F
5. Redraw the skeleton structures for #1 and #4, indicating all polar bonds, using the δ+ and δ– notation.
#1 δ + B––Cl δ–
#4 δ + C––F δ–
6.
BCl3
Nonpolar
Zero dipole moment
SeF4
Polar
Nonzero dipole moment
CHM 1220/1225
Exam II A Answers
Page 2 of 2
7.
Arrangement of pairs
Octahedral
Trigonal planar
Tetrahedral
a.
b.
c,
Molecular Geometry (Shape)
Square pyramidal
Bent or angular or vee-shape
Trigonal pyramid
8.
Hybridization of the central atom
a.
b.
c.
9. a.
b.
c.
d.
Identify each bond as a
σ-bond or π-bond
Cl–P sigma
S–O one sigma, one pi bond each
P–H sigma
3 2
sp d
2
sp
3
sp
4 + 5 + 1 = 10 valence electrons; KK
/2(8 –2) = 3; diamagnetic
1
/2(6 –2) = 2; paramagnetic
–
CN
1
(σ2s)2 (σ2s*)2
(π2p)4 (σ 2p)2
8.
EXAMPLE
STRUCTURAL UNIT
ATTRACTIVE FORCE BETWEEN UNITS
C6H12O6
Molecule
Intermolecular forces
Ca3(PO4)2
Cations and anions
Ionic bond
atoms
Covalent bond
Postive core of atom
Metallic bond
SiC, Diamond,
Graphite
Choose one metal
SOLID TYPE
MOLECULAR
IONIC
COVALENT NETWORK
METALLIC
10.
Phase Change
Beginning Phase
Sublimation
Solid
Melting
Solid
Evaporation
Liquid
Freezing
Liquid
Condensation
Gas
Deposition (or condensation)
Gas
Which absorb (require) energy (heat). Sublimation; Melting; Evaporation
Ending Phase
Gas
Liquid
Gas
Solid
Liquid
Solid