Teacher Instructions
This lesson can be used to teach Periodicity after the Quantum Model has been taught. The
Quantum Model then becomes a basis for understanding the reasons for the periodic trends.
Do not assign reading about Periodicity before these activities so that this guided Inquiry
can lead them to discover periodic trends. Guided Inquiry can also lead them to discover the
connections between periodicity and the Quantum Model. Many opportunities for Inquiry
exist throughout the activities and will be pointed out in this teacher instruction document.
The students are asked to use Excel to create a graph of the atomic radii versus the atomic
number of the first 53 elements. Students can then be asked to use Excel to graph the
ionization energies versus the atomic number of the first 53 elements. In class the students
will use their graphs, colored pencils or markers, a Periodic Table, and the student
worksheet which follows to analyze and interpret the graphs and to make discoveries about
the periodic trend of atomic radii and ionization energies within Groups and within Periods.
Worksheet questions in Bold indicate the students are being asked to apply their
understanding of the Quantum Model to answer the question.
Students generally need individual help on the worksheet. Walking around the classroom and
responding to student questions is usually adequate to encourage students’ understanding of
the instructions and give them courage to do this guided inquiry. Do not allow text books
and do encourage students to think and make their own hypotheses. Positive reinforcement
should be freely offered when students are struggling. Specific suggestions to the teacher
will be included in the worksheet key.
See worksheets, sample student graphs, and worksheet keys on the following pages.
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ANALYSIS OF PERIODIC PROPERTIES
1.
Using a highlighter, color each of the points on each of the graphs that represent
each element in Group 1.
2. Using a different colored highlighter, color the points on each graph that represent
each element in Group 18.
3. Using a highlighter, enclose in a circle the points on each of the graphs that
represent each element in Period 1.
4. Using a different colored highlighter, enclose in a circle the points on each graph
that represent each Period.
5. Look up the dictionary meaning of the word trend. Write it here.
Graph of Atomic Radii:
6. What trend do you see of the atomic radii within Group 1?
7. What trend do you see of the atomic radii within Group 18?
8. Examine trends of atomic radii in each of the Groups on your graph. Make a
statement that generalizes what happens to the atomic radii within a Group.
9. Make a hypothesis to explain the cause of the trend within Groups.
10. Test your hypothesis and give data that supports/contradicts your hypothesis.
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11. What is the trend of atomic radii within Period 1?
12. What is the trend of atomic radii within Period 2?
13. Examine trends of atomic radii in each of the Periods on your graph. Make a
statement that generalizes what happens to the atomic radii within a Period.
14. Make a hypothesis to explain the cause of the trend within Periods.
15. Test your hypothesis and give data that supports/contradicts your hypothesis.
Graph of IONIZATION ENERGY:
16. Which Group of elements has the lowest first Ionization Energies?
17. Which Group of elements has the highest first Ionization Energies?
18. Describe the trend in I.E. within a Group.
19. Describe the trend in I.E. within a Period.
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20. Define Ionization Energy.
21. Make a hypothesis to explain the trend of Ionization Energy within a Group.
22. Test your hypothesis and give data that supports/contradicts your hypothesis.
23. Make a hypothesis to explain the trend of Ionization Energy within a Period.
24. Test your hypothesis and give data that supports/contradicts your hypothesis.
25. Choose the correct word in the following statements that generally describe the
relationships between atomic numbers, atomic radii, and first ionization energy:
Atomic radii (increase, decrease) down a Group.
Atomic radii (increase, decrease) across a Period.
Ionization energies (increase, decrease) down a Group.
Ionization energies (increase, decrease) across a Period.
Trends in atomic radii and ionization energies within Groups and Periods are
(the same, opposite).
26. Explain how these two graphs demonstrate Periodicity.
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TEACHER KEY TO ANALYSIS OF PERIODIC PROPERTIES
1.
Using a highlighter, color each of the points on each of the graphs that represent
each element in Group 1. The teacher should walk around and check students’ work,
and answer questions with questions, if possible. Example: Student: “How do I know
which elements are in Group 1?” Teacher: “Can you use the Periodic Table to identify
them?” See accompanying graph.
2. Using a different colored highlighter, color the points on each graph that represent
each element in Group 18. Same idea as question 1.
3.
Using a highlighter, enclose in a circle the points on each of the graphs that
represent each element in Period 1. Same idea as question 1.
4. Using a different colored highlighter, enclose in a circle the points on each graph
that represent each Period. See completed graph.
5. Look up the dictionary meaning of the word trend. Write it here.
General direction
Graph of Atomic Radii:
6. What trend do you see of the atomic radii within Group 1?
The atomic radii increase as you go down the Group.
7. What trend do you see of the atomic radii within Group 18?
The atomic radii increase as you go down the Group.
.
8. Examine trends of atomic radii in each of the Groups on your graph. Make a
statement that generalizes what happens to the atomic radii down a Group.
Radii increase within each Group.
9. What is the trend of atomic radii across Period 1?
The atomic radii decrease as you go across the Period.
10. What is the trend of atomic radii across Period 2?
The atomic radii decrease as you go across the Period.
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11. Examine trends of atomic radii in each of the Periods on your graph. Make a
statement that generalizes what happens to the atomic radii across a Period.
Atomic radii decrease as you go across the Period.
12. Make a hypothesis to explain the cause of the trend of atomic radii within
Groups.
This is a question that elicits shallow answers at first: “The radii get
bigger because there are more protons and electrons.”…..This is where the teacher
can guide the Inquiry by saying, “Yes, but aren’t there more electrons and protons
as you go across the Period? And do the radii increase there?” Then the students
might be challenged to think about the Quantum Model when they try to explain the
trend. Students might then give the correct answer: “The radii increase as you go
down the Group because electrons are in higher energy levels, which have a greater
distance from the nucleus.”
13. Test your hypothesis and give data that supports/contradicts your hypothesis
Students usually give 1s1, 2s1, 3s1, and 2p8, 3p8 , etc. as evidence to
support their hypothesis.
14. Make a hypothesis to explain the cause of the trend within Periods.
This is very difficult for students, and they usually cannot answer this
unless they do research outside of class on the Internet or sometimes their
textbook. I applaud their efforts of discussing this and applaud their arguments
and questions. Usually if you leave it open with no penalty, some student will come
back with the answer the next day:
“The radii decrease in the period because the electrons are being added to the
same energy level but are being pulled by stronger positive charge as more protons
are in the nucleus.”
15. Test your hypothesis and give data that supports/contradicts your hypothesis.
Students can test the above hypothesis by writing the outer electron
configuration of a couple of periods: 2s22p7 3s23p5 etc. showing electrons in same
energy level as the number of protons increases.
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Graph of IONIZATION ENERGY:
16. Which Group of elements has the lowest first Ionization Energies?
Group 1
16. Which Group of elements has the highest first Ionization Energies?
Group 17
17. Describe the trend in I.E. down a Group.
I.E. decreases in a Group
18. Describe the trend in I.E. across a Period.
I.E. increases in a Period
19. Define Ionization Energy:
Energy required to remove the first electron from a neutral gaseous atom in
its ground state at 0 K to infinity.
20. Make a hypothesis to explain the trend of Ionization Energy within a Group.
Using the same teaching strategy as for the previous hypotheses, encourage the
students to think Quantum Model explanations. This usually leads to the
realization that electrons at a greater distance from the nucleus (higher energy
levels) will have less force acting on them by the protons and will therefore be
easier to rip off. (Lower ionization energy).
21. Test your hypothesis and give data that supports/contradicts your hypothesis.
Students can cite the electron configurations again: 1s1, 2s1, 3s1, and 2p8, 3p8
and state that the distances from the nucleus increase with energy levels.
22. Make a hypothesis to explain the trend of Ionization Energy across a Period.
Students can usually think of more protons exerting more force on electrons at
approximately the same distance from the nucleus (same energy level),
therefore making the ionization energy higher.
23. Test your hypothesis and give data that supports/contradicts your hypothesis.
Students can test the above hypothesis by writing the outer electron
configuration of a couple of periods: 2s22p7 3s23p5 etc. showing
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electrons in same energy level as the number of protons increases and
therefore exerts more force on those electrons.
24. Choose the correct word in the following statements which generally describe the
relationships between atomic numbers, atomic radii, and first ionization energy:
Atomic radii (increase, decrease) down a Group.
Atomic radii (increase, decrease) across a Period.
Ionization energies (increase, decrease) down a Group.
Ionization energies (increase, decrease) across a Period.
Trends in atomic radii and ionization energies within Groups and Periods are
(the same, opposite).
25. Explain how these two graphs demonstrate Periodicity.
The trend
The trend
The trend
Group.
The trend
Period.
in atomic radii within a Group is repeated with each new Group.
in atomic radii within a Period is repeated with each new Period.
in ionization energy within a Group is repeated with each new
in ionization energy within a Period is repeated with each new
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