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Model 2. Energy Level Diagrams for Helium, Neon, and Argon

Model 2. Energy Level Diagrams for Helium, Neon, and Argon

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ChemActivity 9



The Shell Model (III)



59



Exercises

1. a) Based on our revised shell model, how many peaks would be expected in a

photoelectron spectrum of lithium? b) What would you expect the relative sizes of

the peaks to be? c) The 1s ionization energies for H, He, and Li are 1.31, 2.37, and

6.26 MJ/mole, respectively. Explain this trend. d) The first ionization energies for

H and Li are 1.31 and 0.52 MJ/mole, respectively. Explain why the Li first

ionization energy is lower.

2. Answer Ex. 1a and 1b for beryllium and for carbon.

3. Sketch the energy level diagram (as in Model 2) for Be and for C.

4. What element do you think would give rise to the photoelectron spectrum shown

below? Explain your reasoning.



Problems

1. Indicate whether each of the following statements is true or false and explain your

reasoning:

a) The photoelectron spectrum of Mg2+ is expected to be identical to the

photoelectron spectrum of Ne.

b) The photoelectron spectrum of 35Cl is identical to the photoelectron

spectrum of 37Cl.

2. The energy required to remove a 1s electron from F is 67.2 MJ/mole. The energy

required to remove a 1s electron from Cl is: a) 54 MJ/mole; b) 67.2 MJ/mole; c)

273 MJ/mole; d) a 1s electron cannot be removed from Cl. Explain.



60



ChemActivity



10



Electron Configurations

(How Are Electrons Arranged?)



Model: Ionization Energies and Electron Configurations.

Table 1.



Ionization energies (MJ/mole) for the

first 18 elements.

Element

1s

2s

2p

3s

H

1.31

He

2.37

Li

6.26

0.52

Be

11.5

0.90

B

19.3

1.36

0.80

C

28.6

1.72

1.09

N

39.6

2.45

1.40

O

52.6

3.04

1.31

F

67.2

3.88

1.68

Ne

84.0

4.68

2.08

Na

104

6.84

3.67

0.50

Mg

126

9.07

5.31

0.74

Al

151

12.1

7.19

1.09

Si

178

15.1

10.3

1.46

P

208

18.7

13.5

1.95

S

239

22.7

16.5

2.05

Cl

273

26.8

20.2

2.44

Ar

309

31.5

24.1

2.82



Table 2.



Electron configurations of

selected elements.

Element

Configuration

1

H

1s

He

1s2

Be

1s2 2s2

C

1s2 2s22p2

Ne

1s2 2s22p6

Mg

1s2 2s22p6 3s2



3p



0.58

0.79

1.06

1.00

1.25

1.52



ChemActivity 10 Electron Configurations



61



Critical Thinking Questions

1. What is the first ionization energy of:

a)



N?



b)



Ar?



2. Give an experimental method for obtaining the data in Table 1.

3. What information is provided by an electron configuration?



4. What is the relationship between the data in Tables 1 and 2?



5. Is it possible to deduce the electron configuration for an atom from its photoelectron

spectrum? If so, describe how. If not, describe why not.



6. We will now construct two possibilities for the photoelectron spectrum of K.

a)



First, consider the first three shells (18 electrons) of K. For these 18

electrons, estimate the IEs [Hint: compare to Ar.] and indicate their relative

intensities.



b)



If the 19th electron of K is found in the n = 4 shell, would the ionization

energy be closest to 0.42, 1.4, or 2.0 MJ/mole? Explain. [Hint: compare to

Na and Li.] Show a predicted photoelectron spectrum based on this

assumption.



62



ChemActivity 10 Electron Configurations



c)



If the 19th electron of K is found in the third subshell of n = 3, would the

ionization energy be closest to 0.42, 1.4, or 2.0 MJ/mole? Explain. [Hint:

compare to other cases in which a new subshell appears.] Show a predicted

photoelectron spectrum based on this assumption.



Exercises

1. Explain why more energy is required to remove an electron from the 1s orbital of

Na (104 MJ/mole) than to remove an electron from the 1s orbital of Ne (84

MJ/mole).

2. According to the data in Table 1, would it require less than 0.50 MJ/mole, 0.50

MJ/mole, or more than 0.50 MJ/mole to remove a 3s electron from the Mg+ ion?

Explain.



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64



ChemActivity



11



Electron Configurations and the

Periodic Table

(How Many Subshells Are There?)



Model 1. Simulated Photoelectron Spectrum of Potassium.



Table 1. Ionization energies (MJ/mole) for selected elements.

Element

1s

2s

2p

3s

3p

3d

4s

K

347

37.1

29.1

3.93

2.38

0.42

Ca

390

42.7

34.0

4.65

2.90

0.59

Sc

433

48.5

39.2

5.44

3.24

0.77

0.63



Critical Thinking Questions

1. Which of your predicted spectra from CTQ 6 of ChemActivity 10 provides the

better match to the experimental spectrum, Model 1? Explain.



ChemActivity 11



Electron Configurations and the Periodic Table



65



2. Based on the analysis we have used to assign peaks in photoelectron spectra to

shells and subshells in atoms, why is the peak at 0.42 MJ/mole in the K spectrum

assigned to the n = 4 shell (as opposed to being another subshell of n = 3)? Refer to

the data in Table 1 of ChemActivity 10: Electron Configurations.



Model 2. Simulated Photoelectron Spectrum of Scandium.

(The 1s peak occurs at 433 MJ/mole and is not shown in this spectrum.)



Critical Thinking Question

3. In the photoelectron spectrum of Sc, the peak at 0.63 MJ/mole is assigned to the 4s

subshell. Why is the peak at 0.77 MJ/mole in the Sc spectrum assigned as a third

subshell of n = 3 (named 3d) as opposed to being a second subshell of n = 4 (that is,

4p)?



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Model 2. Energy Level Diagrams for Helium, Neon, and Argon

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