Tools for Teachers - Shodor



Tools for Teachers

Chemistry

[pic]

Prepared by the Shodor Education Foundation with support from:

Table of Contents

• Purpose 3

• Draft lesson plans by Topic

- Chemical Bonding 4

- Solubility Rules 5

- Electrolytes 10

- ionic and Net ionic Equations 25

- Photoelectron Inquiry Activity 34

- H2 + Cl2 Limiting Reactant 41

• National Science Digital Library. 45

• Useful Web Links 49

Purpose

In June 2006 North Carolina chemistry teachers gathered at a workshop hosted by the shodor education foundation.

Their goal was produce inquiry lesson plans that would be of immediate value to both new teachers and more seasoned teachers.

The lesson plans were to include, as much as possible, resources from the National Science Digital Library (NSDL) and computational science tools from Shodor’s Computational Science Education Reference Desk (CSERD).

This is a summary of the draft lesson plans that were produced along with a list of links and other information that those attending the workshops found to be particularly useful.

Please use these lessons, change them and improve them. Send the changes to us at: Linda@ or halpin@ncssm.edu or gotwals@ncssm.edu

Let us know if you find the NSDL and other resources useful.

Our thanks to the following teachers who carefully and thoughtfully put together the lesson plans in this document:

Ken Carter

Antoinette Cheek

Guido Gabbrielli

Cathy McLuskey

John Pritchett

Chuck Roser

Ragan Spain

Laura Stiles

CHEMICAL BONDING

Learning Objective: To identify the differences between ionic and covalent bonding.

NC Standards: 2.06, 2.07

Pre-Requisite: An understanding of the difference between metals and non-metals

and their respective locations on the Periodic Table.

Skills: Quantitative measurement, data reading, data analysis

Strand: Nature of science, science as inquiry, science and technology

Safety Precautions: If the conductivity of the solutions are actually measured

instead of using the virtual lab, safety goggles should be worn at

all times and students should not breathe fumes. Hands should

be thoroughly washed after the lab.

Science Concepts: Ionic and covalent bonding

Materials: AlCl3, KOH, CaCl2, C12H22O11, CH3OH, C5H12, distilled water, six beakers, stir rod and conductivity meter

Procedure:

1) Virtual Lab

a. Go to the site

b. Follow the instructions and determine if the light shines brightly for the following 6 compounds

i. AlCl3

ii. KOH

iii. CaCl2

iv. C12H22O11

v. CH3OH

vi. C5H12

c. Complete the data table

2) Actual lab

a. Mark the six beakers with the names of the six compounds .

b. Put 100 mL of distilled water in four of the six beakers.

c. Add one scoop of the first four compounds listed to the beakers labeled with their names to the distilled water and stir with the stir rod. (Rinse and dry the stir rod between each addition.)

d. Put the conductivity probe into the beaker and make certain that the tip is completely under the surface of the solution.

e. Record whether the light shines or does not shine on the data sheet.

f. Repeat steps d and e for the other three solutions.

g. Put 100 mL of CH3OH and 100 mL of C5H12 into the remaining two beakers and cover with a lid.

h. Repeat steps d and e for each of the new compounds. Do not breathe the fumes from either beaker. Only remove the lids long enough to perform the test.

Data Table:

|NAME |FORMULA |LIGHT SHINES |

| | |(YES or NO) |

|Aluminum Bromide |AlBr3 | |

|Potassium Hydroxide |KOH | |

|Calcium Chloride |CaCl2 | |

|Sucrose |C12H22O11 | |

|Methanol |CH3OH | |

|Pentane |C5H12 | |

Questions:

1. Group the compounds based on their ability to enable the light to shine.

2. Using the blank outline of the periodic table supplied, insert the different elements.

3. What is the main difference between the two groups?

4. To which group would you expect LiOH, C2H5OH and NaC2H3O2 to belong?

5. The presence of ions is necessary to conduct electricity. Which group should be labeled as Ionic and which group Covalent?

Teacher Notes:

1. At the end of the questions a more detailed description of the different types of bonding should be given. Suggested internet sites to use in the description are :

a.

b.

c.

d.

e.

2. A good follow-up exercise would be for the students to identify ten simple chemical compounds that they use in their homes and use the Periodic Table to determine if the compounds are ionic or covalent.

3. If the virtual lab is used then it is suggested that one or two live demonstrations are incorporated.

4. This may be a good point to introduce the student to nomenclature.

SOLUBILTY RULES

Learning Objective: To understand the solubility rules and how to apply them

NC Standards: 5.01

Pre-Requisite: An understanding of the difference between ionic and covalent

bonding.

Skills: Quantitative measurement, data reading, data analysis

Strand: Nature of science, science as inquiry, science and technology

Safety Precautions: If the conductivity of the solutions are actually measured

instead of using the virtual lab, safety goggles should be worn at

all times and students should not breathe fumes. Hands should

be thoroughly washed after the lab.

Science Concepts: Solubility

Materials: AlCl3, KOH, CaCl2, AgCl, HC2H3O2, C12H22O11, CH3OH, C5H12, distilled

water, six beakers, stir rod and conductivity meter

Solubility Rules:

Soluble

• All nitrates, acetates, ammonium and Group 1 salts

• All chlorides, bromides and iodides except silver, lead and mercury (I)

• All fluorides except Group IIA, lead (II) and iron (II)

• All sulfates except calcium, strontium, barium, mercury, lead (II) and silver

Insoluble (0.10 M or greater)

• All carbonates and phosphates except Group IA and ammonium

• All hydroxides except Group IA, strontium and barium

• All sulfides except Group IA, IIA and ammonium

• All oxides except Group IA

Procedure:

3) Virtual Lab

a. Go to the site

b. Follow the instructions and determine if the light shines brightly or weakly for the following eight compounds

i. AlCl3

ii. KOH

iii. CaCl2

iv. AgCl

v. HC2H3O2

vi. C12H22O11

vii. CH3OH

viii. C5H12

c. Complete the data table

4) Actual lab

a. Mark the eight beakers with the names of the eight compounds .

b. Put 100 mL of distilled water in six of the eight beakers.

c. Add one scoop of the first six compounds listed to the beakers labeled with their names to the distilled water and stir with the stir rod. (Rinse and dry the stir rod between each addition.) Cover the acetic acid solution with a lid.

d. Put the conductivity probe into the beaker and make certain that the tip is completely under the surface of the solution.

e. Record whether the light shines, weakly shines or does not shine on the data sheet.

f. Repeat steps d and e for the other five solutions.

g. Put 100 mL of CH3OH and 100 mL of C5H12 into the remaining two beakers and cover with a lid.

h. Repeat steps d and e for each of the new compounds. Do not breathe the fumes from either beaker. Only remove the lids long enough to perform the test.

Data Table:

|NAME |FORMULA |LIGHT SHINES |

| | |(YES, WEAKLY or NO) |

|Aluminum Bromide |AlBr3 | |

|Potassium Hydroxide |KOH | |

|Calcium Chloride |CaCl2 | |

|Silver Chloride |AgCl | |

|Acetic Acid |HC2H3O2 | |

|Sucrose |C12H22O11 | |

|Methanol |CH3OH | |

|Pentane |C5H12 | |

Questions:

6. Group the compounds based on their ability to enable the light to shine, shine weakly and not shine.

7. Did any of the covalent compounds allow the light to shine? If the answer is no, explain.

8. Did all the ionic compounds cause the light to shine brightly? If the answer is no, explain.

9. Based on the Solubility Table, what would happen to the light if 0.10 M solutions of CuSO4, Cr2S3, Li2O, FeF3 and (NH4)3PO4 were tested?

10. Using the textbook, or the internet, determine the color of all the solutions.

11. Using the Periodic Table, provide an explanation of the findings in question 5.

12. Did any covalent compounds cause the light to shine weakly? If the answer is yes, explain.

Teacher Notes:

5. At the end of the questions a more detailed description of solubility should be given. Suggested internet sites to use in the description are :

a.

b.

c.

d.

6. If the virtual lab is used then it is suggested that one or two live demonstrations are incorporated.

Strong, Weak, and Non-Electrolytes

This lesson includes:

• Teacher demonstration

• Computer Animations

• Lecture Notes

• Student Notes

• Interactive Power Point Assessment

• Student Assignment

Learning Objectives

Students will use electrical conductivity to:

• Distinguish among strong, weak, and non-electrolytes.

• Compare degrees of dissociation of strong and weak acids and bases.

Standards: 2.06, 2.07, 5.04

Strands: Science as Inquiry, The Nature of Science, Science and Technology

Safety Precautions: If the conductivity of the solutions are actually measured

instead of using the virtual lab, safety goggles should be worn at

all times and students should not breathe fumes. Hands should

be thoroughly washed after the lab.

Science Concepts: solubility, properties of ionic and covalent compounds, degree of

ionization/dissociation, electrolytes

Materials: conductivity tester, water vinegar, sucrose solution, sodium chloride solution

Internet, LCD projector

Student note sheet, Teaches notes

(Note: Student note sheet can be projected on a white board and students can record information as

teacher provides it. A Smart Board may also be used as a way to present student notes.)

Lesson Outline

I. A. Begin lesson with a demo using a conductivity tester that turns on a light bulb when in an electrolytic solution: water, sugar, vinegar, and sodium chloride

C. If a conductivity tester is not available and you have access to the Internet and a LCD projector, use the following animation to show conductivity of the three solutions:



or



B. Students record on their note sheet whether the light bulb comes on bright, dim, or off.

C. Have students suggest what they think is happening to each solute to cause the different observations.

II. A. Show the following animations at

i. Dissolving sugar

ii. Dissolving sodium chloride

B. As Students watch each animation; they should complete each illustration on their note sheet.

C. After students have completed both illustrations, have them predict by illustrating on their note sheet what happens to the acetic acid solution to cause the light bulb to come on dimly.

D. Show the following animations at

i. Strong acid ionization

ii. Weak acid equilibrium

E. After students have watched each animation, they should describe and illustrate on their note sheet what happens to each acid when dissolved in water.

III. Simply define electric currents: Electric current is the flow of electric charge.

IV. A. Define the following terms. Students should record the definitions on their note sheet

i. Strong electrolyte

ii. weak electrolyte

iii. non-electrolyte

B. Show the following animations:



Students should complete the illustrations on their handout as they view these animations by indicating if the light bulb is off, bright or dim and by indicating the species that are present in each solution that the conductivity tester is placed in and if each solution is a non-, weak, or strong electrolyte.

V. Provide students with the rules for deciding which compounds are non-, weak, or strong electrolyte

VI. Power Point Tutorial

VII. Assignment

Conductivity Demonstration Observations

• In the data table below, record what happens to the light bulb as each substance/solution is tested with the conductivity tester.

Data Table 1.

|Substance/Solution |Light Bulb |

|Water, H2O | |

|Sucrose, C12H22O11 (aq) | |

|Sodium chloride, NaCl (aq) | |

|Vinegar/Acetic Acid, HC2H3O2 (aq) | |

• What do you think happens when each substance – sucrose, sodium chloride, and acetic acid – are dissolved in water to cause the light bulb to remain off or come on brightly or dimly?

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________________

Dissolving of sucrose (sugar) in water

• View the animation of the sugar dissolving in water.

• Complete the illustration below to show what is happening to the sugar molecules as they dissolve.

Dissolving of sodium chloride (salt) in water

• View the animation of the sugar dissolving in water.

• Label the large and small particles as a positive sodium ion, Na+1, and negative chloride ions, Cl-1.

• Complete the illustration below to show what is happening to the sodium and chloride ions as they dissolve.

• Based on your observations of the dissolving of sucrose and sodium chloride in water, illustrate what you believe happens to the acetic acid, HC2H3O2, when it dissolves in water to turn the light bulb on dimly.

• Watch the animation of a strong acid ionization.

• Describe and illustrate what happens to the acid when dissolved in water.

• Do all acid molecules ionize?_________________________________________________

• Watch the animation of a weak acid equilibrium.

• Describe and illustrate what happens to the acid when dissolved in water.

• Do all acid molecules ionize? _____________________________________________________

• Referring back to your illustration of the dissolving of sucrose (sugar), describe how the two acid ionizations are different from the dissolving of sucrose in water.

________________________________________________________________________________

________________________________________________________________________________

_________________________________________________________________________________

Electric current –

Electrolytes–

• Strong electrolyte -

• Weak electrolyte -

• Non- electrolyte -

Complete the illustrations as you view the electrolyte animations:



[pic] [pic] [pic]

_________________ __________________ ___________________

• In the blank below each container above, label each solution above as a strong, weak or non-electrolyte.

How to decide if a compound is a non-electrolyte, weak electrolyte, or strong electrolyte.

Strong electrolytes

• Strong acids – HCl, HBr, HI, H2SO4, HNO3, HClO4, HClO3

• Strong bases – Group IA hydroxides, Ca(OH)2, Sr(OH)2, Ba(OH)2

• Soluble ionic compounds

Weak electrolytes

• weak acids

• weak bases

Non-electrolytes

• molecular compounds– bonding is covalent

• Insoluble ionic compounds

Conductivity Demonstration Observations

• In the data table below, record what happens to the light bulb as each substance/solution is tested with the conductivity tester.

Data Table 1.

|Substance/Solution |Light Bulb |

|Water, H2O |Off |

|Sucrose, C12H22O11 (aq) |Off |

|Sodium chloride, NaCl (aq) |Bright |

|Vinegar/Acetic Acid, HC2H3O2 (aq) |Dim |

• What do you think happens when each substance – sucrose, sodium chloride, and acetic acid – are dissolved in water to cause the light bulb to remain off or come on brightly or dimly?

Teacher records students answers

Dissolving of sucrose (sugar) in water

• View the animation of the sugar dissolving in water.



• Complete the illustration below to show what is happening to the sugar molecules as they dissolve.

Dissolving of sodium chloride (salt) in water

• View the animation of the sugar dissolving in water.



• Label the large and small particles as a positive sodium ion, Na+1, and negative chloride ions, Cl-1.

• Complete the illustration below to show what is happening to the sodium and chloride ions as they dissolve.

• Based on your observations of the dissolving of sucrose and sodium chloride in water, illustrate what you believe happens to the acetic acid, HC2H3O2, when it dissolves in water to turn the light bulb on dimly.

• Watch the animation of a strong acid ionization.

• Describe and illustrate what happens to the acid when dissolved in water.

• Do all strong acid molecules ionize?_________________________

Allow students time to complete their illustrations then draw an illustration fro students or have students share their drawings.

• Watch the animation of a weak acid equilibrium.

• Describe and illustrate what happens to the acid when dissolved in water.

• Do all weak acid molecules ionize? _________________________

Allow students time to complete their illustrations then draw an illustration fro students or have students share their drawings.

• Referring back to your illustration of the dissolving of sucrose (sugar), describe how the two acid ionizations are different from the dissolving of sucrose in water.

Strong acids ionize 100%

Weak acids partially ionize

Although sucrose does dissolve in water, the molecules do not ionize

Electric current – flow of electric charge

Electrolytes–

• Strong electrolyte – 100% ionization when dissolved in water

• Weak electrolyte – partial ionization when dissolved in water

• Non- electrolyte – no ionization when dissolved in water

Complete the illustrations as you view the electrolyte animations:



[pic] [pic] [pic]

Non-electrolyte Weak electrolyte Strong electrolyte

• In the blank below each container above, label each solution above as a strong, weak or non-electrolyte.

How to decide if a compound is a non-electrolyte, weak electrolyte, or strong electrolyte.

This is a good place to review solubility rules

Strong electrolytes

• Strong acids – HCl, HBr, HI, H2SO4, HNO3, HClO4, HClO3

• Strong bases – Group IA hydroxides, Ca(OH)2, Sr(OH)2, Ba(OH)2

• Soluble ionic compounds

Weak electrolytes

• weak acids

• weak bases

Non-electrolytes

• molecular compounds– bonding is covalent

• Insoluble ionic compounds

Conductivity Tester Templates[pic]

[pic][pic][pic]

Ionic & Net Ionic Equations

This lesson includes:

• Computer Animations

• Lecture Notes

• Student Notes

Prerequisites:

Students should be able to:

• Write formulas and name compounds.

• Balance equations.

• Identify reaction types.

• Predict products.

• Use solubility rules to determine if a substance is soluble or insoluble in water.

Learning Objectives

Students will:

• Use the state of matter symbols: (s), (l), (g), (aq)

• Write and balance ionic equations.

• Write and balance net ionic equations for double replacement reaction.

Standards: 2.03, 5.01, 5.02, 5.03

Strands: Science as Inquiry, The Nature of Science, Science and Technology

Safety Precautions: If performing reaction demos (single and double replacement ractions) instead of using the virtual lab, safety goggles should be worn at all times and students should not breathe fumes. Hands should be thoroughly washed after the lab.

Science Concepts: solubility, properties of ionic and covalent compounds, degree of

ionization/dissociation, electrolytes

Materials: Internet, LCD projector

Student note sheet, Teaches notes

(Note: Student note sheet can be projected on a white board and students can record information as

teacher provides it. A Smart Board may also be used as a way to present student notes.)

happens to soluble ionic compounds when dissolved in water?

Example 1. View the double displacement reaction animation:



Before starting the animation, complete the following:

• Referring to the solubility rules, determine if lead nitrate, Pb(NO3)2 , and potassium iodide, KI, are soluble or insoluble in water.

Pb(NO3)2 ___________________ KI _______________________

• Illustrate the particles that are present in each beaker.

• Why is there one Pb+2 ion and two NO3-1ions present in the first beaker?

______________________________________________________________________________________________________________________________

• Why is there one K+1 ion for every I-1 ion in the second beaker?

______________________________________________________________________________________________________________________________

• Describe the relationship between the number of ions present in each beaker and the formula for each compound. _______________________________________________________________

_______________________________________________________________

• Describe the relationship between the state of matter symbol and the solubility of each reactant.

_______________________________________________________________

_______________________________________________________________

Start the animation.

After two PbI2 compounds have been formed, stop the animation and complete the following:

• Why did one Pb+2 ion react with two I-1 ions? _______________________________________________________________

_______________________________________________________________

• Describe what is happening to the K+1 and NO3-1 ions. _______________________________________________________________

_______________________________________________________________

• In the box below, illustrate what is present in the flask at this point.

• Which product is the precipitate? _________________________

• Which species are the spectator ions? ______________________

• Explain how you know this? _______________________________________________________________

_______________________________________________________________

Finish watching the animation.

• In the box below, illustrate what is in the flask at the end of the reaction.

• Write the chemical formulas for each reactant and product, including the states of each reactant and product.

• Referring to the solubility rules, determine if each product is soluble of insoluble.

PbI2 _________________ KNO3 ____________________

• Describe the relationship between the state of matter symbol and the solubility of each product.

_______________________________________________________________

_______________________________________________________________

Writing Ionic and Net Ionic equations

Balance the equation below.

Pb(NO3)2 (aq) + KI (aq) ( PbI2 + KNO3 (aq)

Separate all the soluble compounds into to positive and negative ions. Keep the equation balanced. This results in the complete ionic equation.

Cross out the ions that appear in the same form on each side of the equation. The ions crossed out are called spectator ions.

Rewrite the equation, omitting the spectator ions. This results in the net ionic equation. This equation should be balanced.

Example 2. View the double displacement reaction animation:



Before starting the animation, complete the following:

• Illustrate the particles that are present in each beaker.

• Describe the relationship between the number of positive and negative ions present in each beaker and the formula for each compound. _______________________________________________________________

_______________________________________________________________

• Describe the relationship between the state of matter symbol and the solubility of each reactant.

_______________________________________________________________

_______________________________________________________________

Start the animation.

After about two water molecules, H2O, have been formed, stop the animation and complete the following:

• In the box below, illustrate what is present in the flask at this point.

• Which species are the spectator ions? ______________________

• Explain how you know this? ___________________________________________________________

_______________________________________________________________

Finish watching the animation.

• In the box below, illustrate what is in the flask at the end of the reaction.

• Write the chemical formula for the reactants and products, including the states of each reactant and product.

• Describe the relationship between the state of matter symbol and the solubility of each product.

_______________________________________________________________

Balance the equation below.

HCl(aq) + NaOH(aq) ( NaCl(aq) + H2O(l)

Separate all the soluble compounds into to positive and negative ions. Keep the equation balanced. This results in the complete ionic equation.

Cross out the ions that appear in the same form on each side of the equation. The ions crossed out are called spectator ions.

Rewrite the equation, omitting the spectator ions. This results in the net ionic equation. This equation should be balanced.

Example 3. View the single displacement reaction animation:



Before starting the animation, complete the following:

• Illustrate the particles that are present before the reaction begins..

• Describe the relationship between the number of positive and negative ions present in the beaker and the formula for AgNO3. _______________________________________________________________

_______________________________________________________________

• Describe the relationship between the state of matter symbol and the solubility of the AgNO3.

_______________________________________________________________

_______________________________________________________________

• What state of matter symbol would you include with the copper, Cu?

Start the animation.

After about two Cu+2 ions have been formed, stop the animation and complete the following:

• In the box below, illustrate what is present in the beaker at this point.

• Why does it take 2 Ag+1 ions to replace 1 Cu+2 ion? _______________________________________________________________

_______________________________________________________________

• Which species are the spectator ions? ______________________

• Explain how you know this? _______________________________________

_______________________________________________________________

Finish watching the animation.

• Describe the appearance of the copper strip at the end of the reaction?

_______________________________________________________________

• Write the chemical formula for the reactants and products, including the states of each reactant and product.

• Describe the relationship between the state of matter symbol and the solubility of each product.

_______________________________________________________________

______________________________________________________________

Balance the equation below.

AgNO3(aq) + Cu(s) ( Ag(s) + Cu(NO3)2(aq)

Separate all the soluble compounds into to positive and negative ions. Keep the equation balanced. This results in the complete ionic equation.

Cross out the ions that appear in the same form on each side of the equation. The ions crossed out are called spectator ions.

Rewrite the equation, omitting the spectator ions. This results in the net ionic equation. This equation should be balanced.

Watch the following animations:





Write complete ionic and net ionic equations for each.

PHOTOELECTRON SPECTROSCOPY

Learning Objective: To understand the role, location, and nature of electrons in

an atom.

NC Standards: 2.06, 3.01

Pre-Requisite: An understanding of the atom – suggest The Atom Inquiry Activity

Skills: Data analysis

Strand: Nature of science, science as inquiry and science and

technology

Safety Precautions: None

Science Concepts: Understand the different types of orbitals, the

location of electrons, how many electrons are in

each orbital, how many orbitals are in each

sublevel, how ionization energy relates to electron

configuration and how ionization energy relates to

the distance of an atom from the nucleus.

Materials: No additional material needed

Background Information:

Earlier we proposed an atomic model with electrons in orbitals around the nucleus, some further away from the nucleus than others. If an electron is said to occupy an energy level in an atom then each electron must be in an orbital at a particular distance from the nucleus and the energy levels corresponding to these orbitals have a certain energy level.

The next step in the location of the electron required Photoelectron Spectroscopy. In chemistry, spectroscopy is a technique that is used to detect what type, and/or what amount, of a chemical substance might be in a chemical sample. Spectroscopic methods are quite common and popular in areas such as forensic (crime) science, where they are used to detect what might be in a murder victims blood, or what might be in some substance found at a crime scene.

In photoelectron spectroscopy (PES), we can detect what substance we have by measuring the amount of energy needed to remove electrons. All substances contain electrons. Electrons can be added to a substance or removed from a substance. If we add an electron, the substance becomes negatively charged. If we remove an electron, the substance becomes positively charged. We can write this last example as: [pic]

This equation says that we have a molecule (M), and it loses an electron to become M+. How does this happen? Energy is needed to remove the electron. This energy is called the ionization energy. When an electron is removed, we say it is ionized, and the energy needed to do that is the ionization energy (IE).

Where does that energy come from? It can come from light energy, which is called a photon. When energy from a photon (shown in the graphic as squiqqly red arrows) strikes the surface of a substance some of the electrons “ionize”, and leave the substance. The substance now has a positive charge. In photoelectron spectroscopy, we are interested in measuring the energy required to remove these electrons. It is often the case that there is more energy striking the surface than is actually needed to remove the electron(s). When that happens, the electrons also have kinetic energy.

The table below provides a short overview of the process:

|Description |Image |

|In the beginning condition, we have two electrons that |[pic] |

|are bound to the molecule (represented by the letter | |

|“M”. This is called the initial state. | |

|After energy strikes the metal surface, an electron |[pic] |

|moves to the next level, called the vacuum level. Given| |

|that the electron has left a “hole” in the molecule, | |

|there is now a plus charge on the molecule. | |

|The energy required to move the electron from the bound |[pic] |

|state to the vacuum level is known as the ionization | |

|energy (I.E.). It is possible, as is shown here, for | |

|the electron to move past the vacuum level. | |

|Assuming that the electron does move past the vacuum |[pic] |

|level, the extra energy is in the formed of kinetic | |

|energy (K.E.). The metal is now M+ (a | |

|positively-charged metal) plus an ionized, or free, | |

|electron. | |

[pic]

The photoelectron spectrum is a plot of the number of electrons emitted versus their kinetic energy. In the diagram below, the “X” axis is labeled high to low energies so that you think about the XY intersect as being the nucleus.

[pic]

(

[pic]

Orbital names s, p, d, and f stand for names given to groups of lines in the spectra of the alkali metals. Early chemists called the line groups sharp, principal, diffuse, and fundamental.

Electron configuration: a notation describing electrons in an atom. For example

Sodium electrons are represented as1s22s22p63s1. The coefficient tell us the energy level and the superscript tells us the number of electrons in that energy level.

Interpretations from the data:

1. There are no values on the y axis in the tables above. Using the Periodic Table and Table 1, put numbers on the y axis.

2. Label each peak on the graphs above with s, p, d, or f to indicate the suborbital they represent..

3. What is the total number of electrons in a neutral potassium atom?

4. How does the number of electrons in a neutral potassium atom relate to the Atomic Number of potassium?

5. Potassium loses one electron when forming an ion. Which electron is mostly to be removed to form K+? _______________ Explain _______________________________________________________

_____________________________________________________________________________

6. Sketch a photoelectric spectrum of calcium. (Don’t try to make it to scale)

7. What is the trend in ionization energy for electrons as they move further from the nucleus?

8. Why is the ionization energy for the 1s orbital in calcium greater than the ionization energy of the 1s orbital in potassium? __________________________________________________________________

9. What element could have the following spectrum? __________

[pic]

10. Examine the graph below.

[pic]

a) Which electron(s) is represented by the 0.77 peak?________________

b) Which electron(s) is represented by the 0.63 peak? _______________

c) Scandium looses two electrons when forming Sc2+. Which electrons are most likely to be removed? __________________________.

Explain the logic for your answer. ____________________________________________

11. Draw a model of a scandium atom by sketching the relative distance of each energy sublevel from the nucleus. Describe how your model compares to the spectrum in #6.

12. Using the Periodic Table, what is the relationship between sublevels and the number of orbitals within each sublevel?

13. Sketch a spectrum of bromine ( label the “Y” axis quantitatively but not the “X” )

14. Write the electron configuration of the following.

a. K b. K+

c. Ca d. Ca2+

e. Sc f. Sc2+

Teacher notes:

This activity should be done after “The Atom” activity. You should discuss the break //in the “X” axis and why it is drawn this way.

The following is a more complete explanation of photoelectron spectroscopy. You way wish to us with your honors or advanced students.

We can use mathematics to describe the concept above. We can write this equation:

[pic]

This equation states that the ionization energy (IE) is equal to the amount of energy coming in (the photon energy, represented by hv) minus the kinetic energy of the electron.

If we have a neutral (uncharged) molecule that is a gas, the photon (hv) ionizes the molecule (M), and leaves the molecule in a positively charged ion state (Mi+). We also now have a free electron (e-): [pic]

We can rearrange the mathematics to show that the ionization energy is also a measure of the difference in energy between the positive ion state Mi+ and the initial state of the molecule M.

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The difference between the energy found in the bound state (also known as the ground state) and the vacuum level (also known as the excited state) is what we measure in photoelectron spectroscopy, or PES. Spectroscopy is the technique in chemistry where we measure the interactions between light energy (photons) and some molecule or molecular system.

We can measure ionization energies using a number of techniques, including molecular modeling. One of the quantities that can be measured are the energies of the molecular orbitals, or MOs. Two of the MOs are of particular interest: the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO). These orbitals are the most important in terms of chemical reactivity. If an electron in a molecule is going to leave, it’s probably going to leave from the HOMO. If an electron is going to be added to a molecule, it’s probably going to find its home in the LUMO. Collectively, these orbitals are known as the frontier orbitals (because they are on the “frontier” of chemical reactivity). More importantly, Koopman’s Theorem states this: the value of the HOMO is also the value of the ionization energy. Thus, we can use molecular modeling to calculate the HOMO, and from that, immediately derive the ionization energy.

If the students color code the main energy levels in question 11 it would reinforce the difference between main energy levels and sublevels.

The use of a long piece of paper tape in question 13 would beneficial in helping the students better understand the relative distances between sublevels.

Activity and spectrum graphics taken from the Pogil Project activities.

(Photoelective Graphics adapted from , with permission of the author. Photoelectric effect graphic from )

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National Science Digital Library for Teachers



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Undissolved sucrose molecules

Dissolved sucrose molecules

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Undissolved sodium chloride

Dissolved sodium chloride

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Dissolved acetic acid, HC2H3O2

O.1 M C2H5OH

0.1 M NaCl

0.1 M HC2H3O2

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Undissolved sucrose molecules

Dissolved sucrose molecules

[pic]

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[pic]

(

Undissolved sodium chloride

Dissolved sodium chloride

Dissolved acetic acid, HC2H3O2

O.1 M C2H5OH

0.1 M NaCl

0.1 M HC2H3O2

Pb(NO3)2 (aq)

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KI (aq)

HCl (aq)

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NaOH (aq)

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Cu

AgNO3 (aq)

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