Solutions

Exam 2

Form Code
A

Sprin~
2007
1. Only
D
(answer 4) is endothermic (heat is required to melt ice to form liquid water).
The rest of the reactionslstatechanges are exothermic (they give off heat).
2. Use the Rydberg Equation:
lA
=
R
[(l/nf2)

(l/ni2)]
11
h
=
(1.097 x
lo7
m')[(114~)

(1/6*)]
=
3.809 x 10'
m'
h
=
1 13.809 x lo5 m'
=
2.626
x
m
=
2626
nm (answer 5)
3. Answer
5
is correct: the photon emitted from the transition of an electron from n
=
6
to n
=
5 has the least energy of all the transition options given in the question, because the
energy level difference (the AE) between these two levels is less than that between any
of the other levels

the further away from the nucleus of the hydrogen atom, the closer
the energy levels become, and the AE between them becomes closer.
4. Answer 4 (NZF4)
is the only molecule that is not planar.
/\

I'
5. Answer 5 (SF4) is the only molecule that is not tetrahedral.
\

6, Bond polarity is based on the difference in electronegativity (AEN) between the tw
bound atoms. So, NBr
has a AEN of 0, N0
has a AEN of 0.4, PCl
has a AEN of
1.0, and CC
has a AEiN of 0. Therefore PCl
(answer 4) is the most polar bond.
r2
I)
7. The sulfurt~~pitrogen
bond in F3SN is a triple bond (answer 3).
r~*.dl
7;
@
'37
krs+
Ed
w/.lbrmrl
&wy
=
0
I
J
,I
(
fid
(more
s+&bb)
.
7
"PL~~~J<L
044.
:I=:
X
:
.#
F:
I/
,
8.
Molecular polarity is based on the net summation of dipole moments of any polar
bonds within the molecule

that is, if a molecule has a net dipole moment, it is polar.
All of the molecules given have bond dipole moments within their symmetrical
molecules that cancel each other, except for H202
(answer 2) which is a nonlinear
nonsymmetrical molecule and therefore has a net dipole moment and therefore is polar.
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 Spring '07
 Mitchell
 Chemistry, Atom, Reaction, net dipole moment

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