College Physics
11th Edition
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
Section: Chapter Questions
Problem 1CQ: Estimate the order of magnitude of the length, in meters, of each of the following; (a) a mouse, (b)...
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Transcribed Image Text:GOAL Apply the modified Bohr theory to a hydrogen-like atom.
PROBLEM Singly ionized helium, He a hydrogen-like system, has one electron in the 1s orbit when
the atom is in its ground state. Find (a) the energy of the system in the ground state in electron volts
and (b) the radius of the ground state orbit.
STRATEGY Part (a) requires substitution into the modified Bohr model. In part (b) modify the equation
for the radius of the Bohr orbits by replacing e2 by Ze2, where Z is the number of protons in the nucleus.
SOLUTION
(A) Find the energy of the system in the ground state.
Write the equation for the energies of a
hydrogen-like system:
Substitute the constants and convert to
electron volts:
Substitute Z = 2 (the atomic number
of helium) and n = 1 to obtain the
ground state energy:
(B) Find the radius of the ground state.
Generalize to a hydrogen-like atom by
substituting Ze2 for e²:
For our case, n = 1 and Z = 2.
En
En
rn
m.X.2²2²2² (²2)
mk 4
2h²
E₁ = 4(13.6 eV) = -54.4 eV
"1
z²(13.6 eV)
2
n²h²
mk Ze²
=
n²
Z
= 0.0265 nm
-(ao)
n²
(0.0529 nm)
LEARN MORE
REMARKS Notice that for higher Z, the energy of a hydrogen-like atom is lower, which means that the
electron is more tightly bound than in hydrogen. The result is a smaller atom, as seen in part (b).
QUESTION When an electron undergoes a transition from a higher to lower state in singly ionized
helium, how will the energy of the emitted photon compare with the analogous transition in hydrogen?
Explain. (Select all that apply.)
The transition energy will be higher in singly ionized helium.

Transcribed Image Text:REMARKS Notice that for higher Z, the energy of a hydrogen-like atom is lower, which means that the
electron is more tightly bound than in hydrogen. The result is a smaller atom, as seen in part (b).
QUESTION When an electron undergoes a transition from a higher to lower state in singly ionized
helium, how will the energy of the emitted photon compare with the analogous transition in hydrogen?
Explain. (Select all that apply.)
The transition energy will be higher in singly ionized helium.
This happens because the helium atom has more protons.
This happens because the helium nucleus is less massive.
The transition energy will be lower in singly ionized helium.
This happens because the helium atom has more neutrons.
EXERCISE
Repeat the problem for an excited state of doubly-ionized lithium (Z = 3, n = 9).
eV
E2
r2
nm
HINTS: GETTING STARTED
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