Pes Chemistry Webcast 5u75

AP® Chemistry: Exploring Atomic Structure Using Photoelectron Spectroscopy (PES) Data with Jamie Benigna

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Equity and Access Statement  The College Board strongly encourages educators to make equitable access a guiding principle for their AP programs by giving all willing and academically prepared students the opportunity to participate in AP.  We encourage the elimination of barriers that restrict access to AP for students from ethnic, racial and socioeconomic groups that have been traditionally underserved.  Schools should make every effort to ensure their AP classes reflect the diversity of their student population.

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 The College Board also believes that all students should have access to academically challenging course work before they enroll in AP classes, which can prepare them for AP success.  It is only through a commitment to equitable preparation and access that true equity and excellence can be achieved.

Equity and Access: Guiding Questions  What does it mean to “provide all students with access to academically challenging course work before they enroll in AP classes?”  In what way has your math, science or STEM program already either addressed or been challenged by this goal?  What opportunities must be provided in the curricula at all grades to ideally prepare students to compete and succeed in a global economy?

Time to begin … 

Warm welcome to our instructor – Jamie Benigna!

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Be sure to budget about 60 minutes to listen, read and complete the webcast and exercises

Hello from the Instructor  Jamie Benigna • AP Chemistry Teacher, Department Coordinator The Roeper School, Birmingham, Michigan • AP Exam Reader • College Board Consultant • Development Committee Member • Food Stylist and Recipe Contributor to VizChef cooking app

Why a webcast on PES? 

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Chemists rely heavily on various methods of spectroscopy to understand the structure of atoms and molecules that are too small to see directly Photoelectron Spectroscopy (PES) is a powerful instrumental tool for probing the electronic structure of any of the naturallyoccurring elements, as well as materials that contain mixtures of these elements This topic has been included in the redesigned AP® Chemistry course, and may not be well understood by students

Image Source: SPECS GmbH

Course Overview In this webcast we will:

 Review the data that have led to various revisions of the atomic model  Investigate the basic setup of PES instrumentation  Explore the abilities and limitations of PES, and the analysis of the spectra produced by PES.  Share many examples of: • Spectra • Student handouts appropriate for classroom use • Sample assessment items

 Reveal data sources and resources to learn more about PES

Learning Objectives By the end of this webcast, AP® Chemistry teachers will be prepared to teach:

 How PES can be used to probe the electronic structure of atoms,  How the data from PES confirms the shell/subshell model of the atom,  How PES data can be used alongside instruction on electron configurations, electron shielding, and the quantum mechanical model

Setting the Stage

with a few foundational questions

Setting the Stage

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13

Introduction to Photoelectron Spectroscopy (PES)

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Various Models of the Atom + + - - ++- + -+ -+ + Dalton

Thomson

-

++ + ++ + - ++ - -

++ + + ++ + +

Rutherford

Bohr

-

Image sources: http://library.thinkquest.org/13394/angielsk/athompd.html http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec11.html http://mail.colonial.net/~hkaiter/astronomyimages1011/hydrogen_emis_spect.jpg http://.wikimedia.org/wikipedia/commons/9/97/A_New_System_of_Chemical_Philosophy_fp.jpg

Further refinements to these models have occurred with new experimental results

5f

7s 6p

5d

6s 5p

4d

5s 4p 4s 3p 3s 2p 2s 1s

3d

4f

1s 2s 3s 4s 4f 5s 5f 6s 7s

2p 3p 4p

3d 4d

5p

5d

6p 7p

6d

But not all elements ‘follow the rules’ 1s 2s

[Ar]4s1 3d5

[Ar]4s13 d10

3s

1s 2p 3p

4s

3d

4p

5s

4d

5p

6s

5d

6p

7s

6d

7p 4f 5f

How do we know?

hν

  -

hν

-

+

Ionization Energy

Image source: http:// chemistry.beloit.edu/stars/images/IEexpand.g if

Image source: Dayah, Michael. “Dynamic Periodic Table.” Accessed Sept. 5, 2013. http

Ionization Energy Eleme nt

IE1

IE2

IE3

IE4

IE5

IE6

IE7

Na

495

4,560

Mg

735

1,445

7,730

Al

580

1,815

2,740

11,600

Si

780

1,575

3,220

4,350

16,100

P

1,060

1,890

2,905

4,950

6,270

21,200

S

1,005

2,260

3,375

4,565

6,950

8,490

27,000

Cl

1,255

2,295

3,850

5,160

6,560

9,360

11,000

Ar 1,527 2,665 3,945 5,770 7,230 8,780 LO 1.5 - The student is able to explain the distribution of electrons in an atom or ion based upon data.

12,000

LO 1.6 - The student is able to analyze data relating to electron energies for patterns or relationships.

How do we probe further into the atom?   Radiation Type

ν

E

Microwaves

10 – 10

Infrared (IR)

1011 – 1014 Hz

9

11

Hz

10-7 – 10-4 MJ/mol 10-4 – 10-1 MJ/mol

Visible (ROYGBV)

4x1014 – 7.5x1014 Hz

0.2 - 0.3 MJ/mol

Ultraviolet (UV)

1014 – 1016 Hz

0.3 – 100 MJ/mol

X-ray

10 hν

16

– 10

19

-

-

-

Hz -

11+

hν

-

-

-

102 – 105 MJ/mol  

Aspects Probed Molecular rotations Molecular vibrations Valence electron transitions in atoms and molecules Valence electron transitions in atoms and molecules Core electron transitions in atoms

IE1 = 495 kJ/mol

Removing Core Electrons -

-

-

 

-

11+

hν

-

-

-

-

 

   

Radiation Type X-ray

ν 10

16

– 10

19

E Hz

102 – 105

Aspects Probed Core electron transitions

Removing Core Electrons hν

-

-

-

-

  -

11+

hν

-

-

-

 

-

Any frequency of light that is sufficient to remove electrons from the 1st shell can remove electrons from any of the other shells.   = IE + KE

PES Instrument

Image Source: SPECS GmbH, http://www.specs.de/cms/front_content.php?

X-ray or UV Source

Kinetic Energy Energy Kinetic Analyzer Analyzer 6.26

0.52

Binding Energy (MJ/mol)

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

3 +

Kinetic Energy   Analyzer Negative Voltage Hemisphere

       

Slightly Less Negative Voltage Hemisphere

If Kinetic energy is too high… Negative Voltage Hemisphere

Slightly Positive Less Negative Voltage Hemisphere Voltage Hemisphere

If voltage is too high… Negative Voltage Hemisphere

Slightly Positive Less Negative Voltage Hemisphere Voltage Hemisphere

X-ray or UV Source

Kinetic Energy Energy Kinetic Analyzer Analyzer

L i 6.26

Binding Energy (MJ/mol)

Boron 19.3

5 +

5 3 +

5 3 +

5 3 +

5 3 +

5 +

5 3 +

5 3 +

5 3 +

Binding Energy (MJ/mol)

5 3 +

5 3 +

5 3 +

5 3 +

5 3 +

0.52

5 3 +

5 3 +

5 3 +

1.36 0.80

5 3 +

5 3 +

Analyzing Data from PES Experiments

Relative Number of Electrons

Analyzing data from PES 2p

2.0

1s

2s

84.0

4.7

+

90

80

70

60

50

40

30

20

10

Binding Energy (MJ/mol)

Which of the following elements might this spectrum represent? (A)He (B)N (C)Ne (D)Ar

0

Relative Number of Electrons

Analyzing data from PES 2p6 7.9

1s2

2s2

3s2

151

12.1

1.09

3p1 0.58

100

10

1

Binding Energy (MJ/mol)

Given the spectrum above, identify the element and its electron configuration: (A)B (B)Al (C)Si (D)Na

Real Spectrum

Auger Transitions

-

hν

-

-

-

11+

hν

-

-

-

-

Real Spectrum 4 Intensity (x105 counts/s)

3. 5 3

2. 5 2

1. 5 1 .5 0

Copper vs. Chromium

Intensity (x103 counts/s)

6 5 4 3 2 1 0

Mixtures of Elements 4 3.

Intensity (x105 counts/s)

5 3

2. 5 2 1. 5 100 90 1

80

70 60 50 40 30 Binding Energy (MJ/mol)

20

10

0

PES Sample Questions

Sample Question #1 Which element could be represented by the complete PES spectrum below?

Relative Number of Electrons

100

10

1

0.1

Binding Energy (MJ/mol)

(A) Li

(B) B (C) N

(D) Ne

Sample Question #2

Intensity

Which of the following best explains the relative positioning and intensity of the 2s peaks in the following spectra?

Li

12

10

8

6

4

Binding Energy (MJ/mol)

2

0

Intensity

14

Be

14

(A) (B) (C) (D)

12

10

8

6

4

Binding Energy (MJ/mol)

2

0

Be has a greater nuclear charge than Li and more electrons in the 2s orbital Be electrons experience greater electron-electron repulsions than Li electrons Li has a greater pull from the nucleus on the 2s electrons, so they are harder to remove Li has greater electron shielding by the 1s orbital, so the 2s electrons are easier to remove

Sample Question #3 Given the photoelectron spectra above for phosphorus, P, and sulfur, S, which of the following best explains why the 2p peak for S is further to the left than the 2p peak for P, but the 3p peak for S is further to the right than the 3p peak for P?

Binding Energy (A) S has a greater effective nuclear charge than P, and the 3p sublevel in S has greater electron repulsions than in P. (B) S has a greater effective nuclear charge than P, and the 3p sublevel is more heavily shielded in S than in P. (C) S has a greater number of electrons than P, so the third energy level is further from the nucleus in S than in P. (D) S has a greater number of electrons than P, so the Coulombic attraction between the electron cloud and the nucleus is greater in S than in P.

Sample Question #4

Intensity (c/s)

Looking at the complete spectra for Na and K below, which of the following would best explain the relative positioning of the 3s electrons?

Na

105

90

75 60 45 Binding Energy (MJ/mol)

30

15

Intensity (c/s)

130 0

K

400 0

350

300

250 200 150 Binding Energy (MJ/mol)

100

50

Sample Question #4a

4

(A) (B) (C) (D)

3.5

3

Na3s

K-3s

Intensity (c/s)

Looking at the spectra for Na and K below, which of the following would best explain the difference in binding energy for the 3s electrons?

2.5 2 1.5 1 Binding Energy (MJ/mol)

0.5

K has a greater nuclear charge than Na K has more electron-electron repulsions than Na Na has one valence electron in the 3s sublevel Na has less electron shielding than K

0

Sample Question #4b

4

(A) (B) (C) (D)

3.5

3

Na3s

K-3s

Intensity (c/s)

Looking at the spectra for Na and K below, which of the following would best explain the difference in signal intensity for the 3s electrons?

2.5 2 1.5 1 Binding Energy (MJ/mol)

0.5

K has a greater nuclear charge than Na K has more electron-electron repulsions than Na Na has one valence electron in the 3s sublevel Na has less electron shielding than K

0

Sample Question #5

Intensity (counts/s)

Given the photoelectron spectrum below, which of the following best explains the relative positioning of the peaks on the horizontal axis?

Image source: http:// www.rsc.org/ej/JM/2010/b925409a/b925409a-f2.g if

(A) O has more valence electrons than Ti or C, so more energy is required to remove them (B) O has more electron-electron repulsions in the 2p sublevel than Ti and C (C) Ti atoms are present in a greater quantity than O can C in the mixture. (D) Ti has a greater nuclear charge, but the 2p sublevel experiences greater shielding than the 1s sublevel.

Sample Question #6

Intensity (c/s)

Given the photoelectron spectrum of scandium below, which of the following best explains why Scandium commonly makes a 3+ ion as opposed to a 2+ ion? 0.6 0.7 3 7

500 2 1

400 0

300

50

40 30 10 Binding Energy (MJ/mol)

9

8

7

6

5

4

(A) Removing 3 electrons releases more energy than removing 2 electrons. (B) Scandium is in Group 3, and atoms only lose the number of electrons that will result in a noble gas electron configuration (C) The amount of energy required to remove an electron from the 3d sublevel is close to that for the 4s sublevel, but significantly more energy is needed to remove electrons from the 3p sublevel. (D) Removing 2 electrons alleviates the spin-pairing repulsions in the 4s sublevel, so it is not as energetically favorable as emptying the 4s sublevel completely.

3

Example Formative Assessment

Intensity

On the photoelectron spectrum of magnesium below, draw the spectrum for aluminum

100

10

Binding Energy (MJ/mol)

1

Hint: for additional formative assessments, use spectra from previous multiple choice questions

Intensity

Quick Check – Can You Now Translate Between These Representations of Mg?

100

10

Binding Energy (MJ/mol) -

4s 3p 3s 2p 2s

1s

1

Mg

-

-

-

-

-

12+

-

-

-

-

1s2 2s2 2p6 3s2

Using Data to Makes Conclusions About Atomic Structure + + - - + - + - + -+ -+ +Thomso n image source: http://ericsaltchemistry.blogspot.com/2010/10/jj-thomsons-experiments-withcathode.html

++ + + ++ + +

-

- ++ ++ ++ - ++ - Rutherfor d

http://84d1f3.medialib.glogster.com/media/f9/f9a5f2402eb205269b648b14072d9fb3a2f556367849d7feb5cfa

Bohr

Relative Number of Electrons

PES – Data that Shells are Divided into Subshells 2p6 7.9

1s

2s

3s

3p

2

2

2

1

151

12.1

1.09 0.58

100

10

1

Binding Energy (MJ/mol)

Eleme nt

IE1

IE2

IE3

IE4

IE5

IE6

Na

495

4560

Mg

735

1445

7730

Al

580

1815

2740

11,600

Si

780

1575

3220

4350

16,100

P

1060

1890

2905

4950

6270

21,200

S

1005

2260

3375

4565

6950

8490

IE7

27,000

Applicable Science Practices From the AP Chemistry Curriculum Framework:

 SP 3.2 • The student can refine scientific questions

 SP 3.3 • The student can evaluate scientific questions

 SP 6.3 • The student can articulate the reasons that scientific explanations are refined or replaced.

Wrap up and Take Aways

Applicable Learning Objectives From the AP Chemistry Curriculum Framework:  1.5 – The student is able to explain the distribution of electrons in an atom or ion based upon data.  1.6 – The student is able to analyze data relating to electron energies for patterns and relationships.  1.7 – The student is able to describe the electronic structure of the atom, using PES data, ionization energy data, and/or Coulomb’s law to construct explanations of how the energies of electrons within shells in atoms vary.  1.8 – The student is able to explain the distribution of electrons using Coulomb’s law to analyze measured energies.  1.12 – The student is able to explain why a given set of data suggests, or does not suggest, the need to refine the atomic model from a classical shell model with the quantum mechanical model.  1.13 – Given information about a particular model of the atom, the student is able to determine if the model is consistent with specified evidence.  1.14 – The student can justify the selection of a particular type of spectroscopy to measure properties associated with vibrational or electronic motions of molecules.

ing Resources and use the webcast handouts

 Classroom activities • Shells Class Activity • From Shells to Subshells Class Activity

 Teacher resources • Spectrum generator spreadsheet • Peaks compiled (80 elements) • Frequently asked questions

 Testing items • Sample items referenced in this webcast (for classroom use, formative, or summative assessments)

ing Resources (cont.)  Arizona simulated photoelectron spectra http://www.chem.arizona.edu/chemt/Flash/photoelectron.html

 Guided inquiry activities on PES • John Gelder (Oklahoma State University) • Moog and Farrell, Chemistry: A Guided Inquiry • POGIL

 Books on PES technical specs • Van der Heide, Paul. X-Ray Photoelectron Spectroscopy: An Introduction to Principles and Practices. New Jersey: John Wiley & Sons, Inc, 2012. • Ellis, Andrew M., Miklos Feher, and Timothy Wright. Electronic and Photoelectron Spectroscopy: Fundamentals and Case Studies. New York: Cambridge University Press, 2005.

ing Resources (cont.)  AP Chemistry Teacher Community (resources section) https://apcommunity.collegeboard.org/web/apchem

 Spectra search strings • • • • • • •

XPS X-ray photoelectron spectroscopy UVPS ESCA spectroscopy ESCA spectra Photoelectron spectrum Photoelectron spectroscopy

ing Resources (cont.)

Image Source: Shen Laboratory, Stanford University and SLAC National Accelerator Laboratory http://arpes.stanford.edu/facilities_ssrl.htm l

Image source: Inna M Vishik http://www.stanford.edu/~ivishik/inna_ vishik_files/Page452.htm

Take Away You should now feel confident

 Explaining how data informs our understanding of the atom  Using PES and experimental evidence to build mental models of atomic structure  Explaining how a PES instrument collects data and how to analyze spectra

Information Jamie Benigna AP Chemistry Development Committee Member [email protected]

Thank you!  Complete a survey on the course and receive Jamie’s summer reading list!  Survey: https://www.surveymonkey.com/s/3FNCLPG