Chapter 28
Atomic Physics
Quick Quizzes
1.
(b). The allowed energy levels in a oneelectron atom may be expressed as
(
)
2
13.6 eV
n
E
Z
n
= −
2
, where
Z
is the atomic number. Thus, the ground state
(
)
1 level
n
=
in helium, with
, is lower than the ground state in hydrogen, with
.
2
Z
=
1
Z
=
2.
(a). The energy of the photon emitted when the electron in a oneelectron atom makes a
transition from a state having principal quantum number
to one having principal
quantum number
i
n
f
n
is
(
)
2
2
2
1
1
eV
f
i
E
Z
n
n
γ
=
−
i
n
13.6
Thus, for given values of
and
f
n
2
, the energy of the photon emitted by a helium atom,
with
, is four times that of the photon emitted when an electron makes the
corresponding transition in a hydrogen atom, with
Z
Z
=
1
=
.
3.
(a)
For
n
, there are 5 allowed values of
A
, namely
A
= 0, 1, 2, 3, and 4.
5
=
(b)
Since
m
A
ranges from –
A
to +
A
in integer steps, the largest allowed value of
A
(
A
= 4 in
this case) permits the greatest range of values for
m
A
. For
5
n
=
, there are 9 possible
values for
m
A
: 4, 3, 2, –1, 0, +1, +2, +3, and +4.
(c)
For each value of
, there are
A
2
1
+
A
possible values of
. Thus, there is 1 distinct
pair with
A
; 3 distinct pairs possible with
m
A
0
=
1
=
A
; 5 distinct pairs with
; 7
distinct pairs with
; and 9 distinct pairs with
2
=
A
3
=
A
4
=
A
. This yields a total of 25
distinct pairs of
A
and
that are possible when
m
A
5
n
=
.
4.
(d). Krypton has a closed configuration consisting of filled
shells as
well as filled 4
s
and 4
p
subshells. The filled
=1, =2, and =3
n
n
n
3
n
=
shell (the next to outer shell in Krypton)
has a total of 18 electrons, 2 in the 3
s
subshell, 6 in the 3
p
subshell and 10 in the 3
d
subshell.
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CHAPTER 28
Answers to Even Numbered Conceptual Questions
2.
Neon signs do not emit a continuous spectrum. They emit many discrete wavelengths as
could be determined by observing the light from the sign through a spectrometer.
However, they do not emit all wavelengths. The specific wavelengths and intensities
account for the color of the sign.
4.
An atom does not have to be ionized to emit light. For example, hydrogen emits light
when a transition carries an electron from a higher state to the
2
n
=
state.
6.
Classically, the electron can occupy any energy state. That is, all energies would be
allowed. Therefore, if the electron obeyed classical mechanics, its spectrum, which
originates from transitions between states, would be continuous rather than discrete.
8.
The de Broglie wavelength of macroscopic objects such as a baseball moving with a typical
speed such as 30 m/s is very small and impossible to measure. That is,
h mv
λ
=
, is a very
small number for macroscopic objects. We are not able to observe diffraction effects
because the wavelength is much smaller than any aperture through which the object could
pass.
10.
In both cases the answer is yes. Recall that the ionization energy of hydrogen is 13.6 eV.
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 Spring '07
 Smith
 Atom, Energy, Photon, Atomic physics, Atomic orbital, ev

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