Unit Two: Periodic classification of the Elements

Lesson 3: Periodic Properties

Comptencies
Starter Activities
Main Activites

Competencies

Explain the general trends in properties of elements down a group of the Periodic Table
Explain the general trends in properties of elements across a period of the Periodic Table
Deduce the properties of an element from its position in the Periodic Table
Make a charts to show the trends in properties of elements in the Periodic Table

Materials

Periodic table, charts to show trends of properties of the elements in the periodic table, worksheet and concept map.

Note for the teacher

This sub-topic is covered in six periods. So, you may use the first period to group students, explain the procedures of the activities, sharing the tasks and checking whether students understood the process clearly.

You may assign two groups to present two properties in a period. Each group may be given 10minutes to present its work. The two groups together need 20minutes. 10 minutes can be used for questions and answers. The remaining 10 minutes may be used for evaluation. The last day may be used for summary, questions and answers.

Starter activity (5 minutes)

Revising period and group of the periodic table
The following points may be raised for discussion in pairs with their bench mates and respond afterwards.

What are the relationships between elements in a period?
How are elements in a group of the periodic table related?
Do all elements in the same period have the same properties?
Do all elements in the same group have the same properties?
Tell the properties in the period or group you know and their trends.

Pose for some time so that students discuss and let them give their response. Encourage the rest of the class to supplement, amend, object or approve the answers given by a group representative.

Some students may think that all elements in a group are identical in all respects. But you should explain that although elements in a group have the same valence electrons, they have different properties. At this stage introduce properties like: nuclear charge, atomic size, electron affinity, electronegativity, ionization energy and metallic properties.

Students may know some of these properties and their trends in a period and group. After they adequately discussed, check that all of them can give the following summary points:

All elements in a period have the same number of shells and those in the same group have the same number of valence electrons.
However, their physical and chemical properties vary in a period and a group with certain trends that they can explain after they study this lesson.
The periodic properties are: nuclear charge, atomic size, electron affinity, electro negativity, ionization energy and metallic character.

Evaluation

Give them the following evaluation questions: What happens to properties of the elements as you move in a period and a group? List properties of the elements which show some changes across a period and a group of the periodic table.

Main activity (27minutes)

Procedure

Arrange your students into base groups of 6 members randomly. Give numbers 1 to 6 to the students in each base group. Giving number should be carefully done so that if number 1 in group 1 is fast learner, number 2 in group 2 should be fast learner etc. so that in the expert group distribution of students include all kinds of learners.
Let all the number 1’s come together to make one group, all the number 2’s make the second group and all the number 3’s the third group etc. These groups are called expert groups.
Arrange the expert groups according to the following correspondence :
- Group 1................................................ nuclear charge
- Group 2................................................ atomic size
- Group 3................................................ ionization energy
- Group 4................................................ electro negativity
- Group 5................................................ electro negativity
- Group 6................................................ metallic properties
Provide worksheet to each group that contains discussion points. If facilities are not available to supply written worksheet, it is possible to write the points on the chalk board before hand.

Discussion points
1. Nuclear charge
  1. What is nuclear charge?
  2. How the trend does vary along a period? Why?
  3. How the trend does vary in a group? Why?
  4. Give examples by taking one period and one group of the periodic table.
  5. Draw a graph of nuclear charge against group number and a graph of nuclear charge against period number. Compare the two graphs and write down your observation.
  6. What is effective nuclear charge?
  7. Explain trends of the nuclear charge in a period and in a group of the periodic table. Give reasons.
2. Atomic size/ atomic radius
  1. What is atomic size?
  2. How the trend does vary along a period? Why?
  3. What are the factors affecting it along a period?
  4. How the trend does vary in a group? Why?
  5. What factors influence atomic size when descending down a group?
  6. Give example by taking one period and one group of the periodic table. Draw Bohr’s model to explain how atomic size changes along the period and down the group.
  7. Where in the periodic table is the largest atom located? What about the smallest atom?
3. Ionization energy
  1. What is ionization energy?
  2. Give three examples of the ionization of atoms
  3. How is its trend along the period? Why?
  4. What factors influence its trend in the period of the periodic table? Explain the effects of each factor.
  5. How is its trend in the group? Why?
  6. What factors influence its trend in the group of the periodic table? Explain the effects of each factor.
  7. Where in the periodic table is the atom with the largest ionization energy located? What about the atom with the smallest ionization energy?
  8. Do the metals or the non-metals have the highest ionization energy? Why?
4. Electron affinity
  1. What is electron affinity?
  2. Give three examples of reactions to show electron affinity.
  3. How is its trend along the period? Why?
  4. What factors influence its trend in the period of the periodic table? Explain the effects of each factor.
  5. How is its trend in the group? Why?
  6. What factors influence its trend in the group of the periodic table? Explain the effects of each factor.
  7. Where in the periodic table is the atom with the largest electron affinity located? What about the atom with the smallest electron affinity?
  8. Do the metals or the non-metals have the highest electron affinity? Why?
5. Electro negativity
  1. What is electro negativity?
  2. How is its trend along the period? Why?
  3. What factors influence its trend in the period of the periodic table? Explain the effects of each factor.
  4. How is its trend in the group? Why?
  5. What factors influence its trend in the group of the periodic table? Explain the effects of each factor.
  6. Where in the periodic table is the atom with the largest electro negativity located? What about the atom with the smallest electro negativity?
  7. Do the metals or the non-metals have the highest electro negativity? Why?
6. Metallic character
  1. What is Metallic character?
  2. How is its trend along the period? Why?
  3. What factors influence its trend in the period of the periodic table? Explain the effects of each factor.
  4. How is its trend in the group? Why?
  5. What factors influence its trend in the group of the periodic table? Explain the effects of each factor.
  6. Where in the periodic table are the metals located? How about the non-metals?
  7. Where do we find the most metallic element? What about the least metallic element?
Let the students take note of the group’s discussion, and go back to their base group.
In the base group each expert presents and explains his/her topics points to the groups
The members listen to the explanations, ask and answer questions.

You should supervise discussions of the students and avoid any misconceptions they that may result. Some slow learners may encounter difficulty to explain their topics successfully. In such cases it is advisable to assist and encourage by giving some clues.

Evaluation

You can give the following kinds of class work exercises after the lesson so that students can do individually. This gives you the opportunity to know individual student’s performance. Check the works of the students by giving more emphasis to the slow learners. The fast learners should also be challenged by giving additional works depending on the lesson topics.

Here are some sample questions. The first one constitutes effective nuclear charge, atomic size and ionization energy while the second one summarizes the whole lessons on periodic properties. You can construct similar questions and other alternative assessment to evaluate your students. It is believed that such tabular forms of assessment somewhat motivates students by creating some interest. So, the teacher should be creative enough to formulate such questions. However, students may face difficulty in understanding it. To avoid misunderstanding of learners, give them clear and adequate directions.

The following table shows part of a periodic table. Let students answer the following questions related to the table.

Period

Group
IA	IIA	IB	IIB	IIIA	IVA	VA	VIA	VIIA	VIIIA
2	Li	Be			B	C	N	O	F	Ne
3	Na	Mg			Al	Si	P	S	Cl	Ar
4	K	Ca	Sc	Ti	Ga	Ge	As	Se	Br	Kr

Fill in the blank space with the correct term or phrase based on the above table.

The element with the list nuclear charge is (1) _______ and the one with the highest nuclear charge (2) _______ Nuclear charge of S is (3) _______than nuclear charge of Se.
As you go from Na to Cl along the period nuclear charge (4) _______.
Effective nuclear charge (5) _______ from B to Ga while it (6) _______ from Na to Ar.
Shielding or screening effect (7) _______down the group but (8)_______ along the period from left to right.
Atomic size of Li is (9) _______ than that of K.
Element with the least atomic size is (10) _______
Element with highest atomic size is (11) _______
Atomic size of Ca is (12) _______ than atomic size of be because number of (13) _______ increases down the group.
Atomic size (14) _______ from K to Kr because electrons are filled on the same shell, the (15) _______ continuously increase and attraction force increases.

Complete the following concept map using: ionization energy, atomic size, electron affinity, electro negativity and metallic character.

Answer 1:

Li
Kr
Less
Remains the same
Increases
Increases
Increases
Remains the same
Smaller
Ne
K
Larger
Energy levels
Decrease
Nuclear charge

Ionization energy, electron affinity, electro negativity
Nuclear charge
Atomic size, metallic character
Electro negativity, electron affinity
Ionization energy
Metallic Character
Atomic size
Electron negativity
Electron affinity

Concluding activity

Let students come to the chalk board and explain the trends of the periodic properties by using diagrams arrows and other descriptions possible. In this way 12 students can gat opportunity to explain one property each either across a period or along a group. The rest of the class should also be involved by giving corrections if there are mistakes or give approvals for the correct works.