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Unformatted text preview: Chapter 7: Electron Conﬁgurations and the Periodic Table 16. 32. 40. 42. Answer: ((1) < (c) < (a) < (1})
Strategy and Explanation: Use Figure 7.1. The energy of a photon is directly proportional to the frequency (v): Lowest energy (d) radio waves < (c) microwaves < (a) green light < (b) Xrays Highest energy Answer: no Strategy and Explanation: Given the wavelength of light and the minimum energy for ejecting elec1rons from a
metal surface, determine if the light has sufficient energy to cause the photoelectric effect (i.e., eject electrons
from that metal’s surface). We use appropriate length conversions and the equation in Section 7.2 to ﬁnd the energy of the photon. Compare the photon energy to the minimum energy. lfthe photon energy is larger, then
the photon can eject electrons; if the energy is smaller, it cannot. The wavelength is it : 600. am. he _ 6.626 ><10_34 Js><2.998 x108m/s _ = —19
Ephown— A 1x1079 m 3.31x10 J
600. nmx— 1 nm
Elmmm“ : 3.69 x 10—19 J > Ephoton Therefore it has insufﬁcient energy to eject electrons. v/Reasonabie Answer Check: The minimum energy is similar to ones calculated for visible light photons in Section 7.2. These two energies are close, so we probably would not have been able to predict this result before
doing the calculation. Answer: (a), (b), and ((1) Strategy and Explanation: The difference between the energies of the two levels is the energy emitted. The
smaller the energy, the longer the wavelength. When we look at Figure 7.8, we need to find which of the given
levels is closer together than the energy levels represented by n = 1 and n = 4. The energies levels represented
by(a) n= 2 andn=4,(b)n=1andn=3, and(d) n= 3 andn= 5, are closertogetherthann=1andn=4. So,
(a), (b), and ((1) will require radiation with longer wavelength. Answer: 4.198 x 11r19 J, 320.5 nm, ultraviolet Strategy and Explanation: Given the values of n for the initial and ﬁnal states of an electron in a helium cation, He+, and an equation describing the relationship between the electron energy level, the atomic number, Z, and
the quantum number, n, determine the transition energy of the electron and what region of the electromagnetic
spectrum it is in. Adapt the method shown in Section 7.3 on page 284. Subtract the initial energy (n : 5) of the electron from the ﬁnal energy (11 = 3) of the electron in helium. Z = 2 for helium. Use Figure 7 .1 to determine
what part of the spectrum it is in. 2 2
—272(2.179x10’18 J)]—[—2(2.179x1018 J)]=—6.198x1019 J 3 5 —19 E _ _
V: photon = AB: “98"“) J =9.354><1014 s“
h h 6.626x10‘3’4 Js
B
l=c=2.998x10 m/s lnm =320.5nm X
V 9.354 ><1014 s‘1 10‘9 m
This wavelength indicates that the emission produces ultraviolet light. / Reasonable Answer Check: The electron levels in helium are closer together than those in hydrogen because
the nucleus has a morepositive charge. 58. Answer/Explanation: The wave mechanical model of the atom tells us that electrons do not follow simple paths
as do planets. Rather, they occupy regions of space having certain shapes and varying distances around the
nucleus. Hence there are subshells and orbitals that were not part of the Bohr model. ...
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 Fall '08
 NITSCHE

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