1. 7.33
Careful spectral analysis shows that the familiar yellow light of sodium lamps (such as street lamps) is made up of photons of two wavelengths, nm and nm. What is the difference in energy (in joules) between the photons with these wavelengths?
For nm, E= x J
For nm, E= x J
ΔE= (3.377x10-19)-(3.373x10-19)= 3.526x10-22 J
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S.A. McFarland©2006

2. 6.57
From the standard enthalpies of formation, calculate ΔHorxn for the reaction
C6H12(l) + 9O2(g) -> 6CO2(g) + 6H2O(l).
For C6H12(l), ΔHof = kJ/mol.
-3924 kJ
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3. 7.17
A photon has a frequency of 6.0x104 Hz. (a) Convert this frequency into wavelength (in nm). Does this frequency fall in the visible region? (b) Calculate the energy (in joules) of this photon. (c) Calculate the energy (in joules) of 1 mole of photons all with this frequency.
5x1012 nm, not in visible region
4.0x10-29 J
2.4x10-5 J/mol
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S.A. McFarland©2006

4. 7.54
An electron in an atom is in the n=3 quantum level. List all of the possible values for l, ml, and ms that it can have.
For n=3, l= 0,1, or 2.
n=3, l=0, ml= 0, ms= +1/2 or -1/2
n=3, l=1, ml= -1, 0, 1, ms= =1/2 or -1/2
n=3, l=2, ml= -2, -1, 0, +1, +2, ms= =1/2 or -1/2
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5. “Fill up” electrons in lowest energy orbitals (Aufbau principle)? ?
Be 4 electrons
Li 3 electrons
B 5 electrons
C 6 electrons
B 1s22s22p1
Be 1s22s2
Li 1s22s1
He 2 electrons
H 1 electron
He 1s2
H 1s1
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6. The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hund’s rule).
N 7 electrons
F 9 electrons
Ne 10 electrons
O 8 electrons
C 6 electrons
Ne 1s22s22p6
N 1s22s22p3
O 1s22s22p4
C 1s22s22p2
F 1s22s22p5
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7. Order of orbitals (filling) in multi-electron atom
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s
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8. Shielding effect in many-electron atoms
Energy depends on n and l
Compare 1s and 2s
1s lower in energy
1s is “stabilized”
Harder to remove a 1s electron from the atom
First filled are last removed
1s electrons are “happy” because they sit close to the nucleus (+)
2s electrons are “shielded” from the attractive force of nucleus by the 1s electrons
2s electrons easier to remove
Compare 2s and 2p
2s has greater electron density near the nucleus
2s is shielded less by the 1s electrons (more penetrating)
2s electrons more strongly held by nucleus
Penetrating power decreases as l increases (s > p > d > f > …)
2s lower in energy
Harder to remove a 2s electron
Easier to remove a 2p electron
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9. in the orbital or subshell
Electron configuration is how the electrons are distributed among the various atomic orbitals in an atom.
number of electrons
in the orbital or subshell
1s1
principal quantum
number n
angular momentum
quantum number l
Orbital diagram
1s1 H
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10. Noble gas core
The electronic configuration of all elements except H and He can be represented by a noble gas core, which abbreviates all core electrons as the nearest noble gas (noble gas that precedes the element of interest.
For instance, Li:
[He]2s1
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11. Core vs. valence electronsLi
1s22s1
[He]2s1
valence (outermost shell)
core
Valence electrons will determine chemical properties such as bonding
and reactivity.
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S.A. McFarland©2006

12. What is the electron configuration of Mg?
Mg 12 electrons
1s < 2s < 2p < 3s < 3p < 4s
1s22s22p63s2
= 12 electrons
Abbreviated as [Ne]3s2
[Ne] = 1s22s22p6
What are the possible quantum numbers for the last (outermost) electron in Cl?
Cl 17 electrons
1s < 2s < 2p < 3s < 3p < 4s
1s22s22p63s23p5
= 17 electrons
Last electron added to 3p orbital
n = 3
l = 1
ml = -1, 0, or +1
ms = ½ or -½
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13. 11/27/2018
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14. Exceptions Cr 1s22s22p63s23p64s23d4 [1s22s22p63s23p6]4s23d4 [Ar]4s23d4
There are several exceptions to the rules for assigning electrons to atomic orbitals. Learn these for Cu and Cr. Cr
1s22s22p63s23p64s23d4
[1s22s22p63s23p6]4s23d4
[Ar]4s23d4
[Ar]4s13d5
Cu also displays this irregularity
Slightly greater stability is associated with the half-filled (3d5) and completely filled (3d10) subshells
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15. Outermost subshell being filled with electrons
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16. 7.85
The electron configuration of a neutral atom is 1s22s22p63s2. Write a complete set of quantum numbers for each of the electrons. Name the element.
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S.A. McFarland©2006

17. 7.104
Only a fraction of the electrical energy supplied to a tungsten lightbulb is converted to visible light. The rest of the energy shows up as infrared radiation (heat). A 75-W lightbulb converts 15.0% of the energy supplied to it into visible light (assume the wavelength to be 550 nm). How many photons are emitted by the lightbulb per second? (1 W = 1 J/s)
11/27/2018
S.A. McFarland©2006