CHM 217 Sections 203 & 204
Quiz #3: Key.
1. What are you going to do today?
Today we are going to discuss and practice Lewis structures, formal charges, and shape
of the molecules (VSEPR).
2. The formula for energy levels of one-electron atoms/ions is
!
En="RZ 2
n2
. Calculate
the energy of photon emitted during the transition from n=3 to n=2 state in He+ ion.
The Rydberg constant R equals 2.18*10-18J.
The energy difference between n=2 and n=3 levels of He+ ion is
!
"E3#2=E2$E3=$R* 22
22$$R* 22
32=$4R*1
4$1
9
%
&
' (
)
*
"E3#2=$1.21*10$18 J
The energy of electron emitted during n=3n=2 transition equals the absolute value of
the difference between the energy of the n=2 and n=3 levels; ie energy of the photon is
1.21*10-18 J.
3. Draw Lewis structures for following molecules:
CH4 C2H4
C H
H
H
H
C
H
H
C
H
H
H2CO CO2
OC
H
H
OCO
4. Which of the following are unacceptable in the lab (the correct answers are in bold):
Coca-Cola Pepsi-Cola Sprite Mountain Dew PB&J sandwich
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