Unit Two: Periodic classification of the Elements

Lesson 2: Classification of the elements

• Comptencies
• Starter Activities
• Main Activites

Competencies 

• Describe the three classes of the elements in the modern Periodic Table
• Describe  the four blocks of the elements in the periodic table in relation to   their electronic configuration
• Tell the block of an element from its electronic configuration

Materials

• Periodic table
• Concept map chart

Starter activities (6 minutes)

This lesson can be started by revising the relationship between electron configuration and the periodic classification of the elements.

Provide students an activity to find the group and period numbers of the elements with atomic numbers: 6, 15 and 19.

Let a few students come forward to write the electron configuration of one element on a chalk board and assign the group and period numbers. The remaining students should give comments on the works.

At this level students should write the electron configurations both in main energy levels and sub-energy levels Atomic number 6: - 2, 4 or 1s2 2s2 2p2 because this element has two main energy levels, it is located in period 2. Similarly, it has 4 electrons in the outer most shell, L-shell ( 2s and 2p), it is located in group 4 of the periodic table.

Evaluation

Students can be asked how one can find out the period and group numbers of an element.

Main activity (25 minutes)

Procedure

1. Arrange students in groups depending on the class size.
2. Let each group elect chair man and secretary

   The following activity may be printed and given for each group or can be written on the chalk board before hand.

3. Give them the following four groups of hypothetical elements with atomic numbers. 11A,
   1. 38B, 4C, 19D
   2. 8E, 13F, 35G, 5H
   3. 24I, 40J, 30K, 21L
   4. 58M, 90Q, 64 R, 66T
4. Write the electron configuration of each member    and answer the following questions in group.
   1. What is the similarity in electron configuration among members of each group?
   2. Write valence electrons configuration of each group of the elements.
   3. In which of the group(s) do all members (elements) have valence electrons in the same energy level?
   4. In which of the group(s) do members have valence electrons in different energy levels?
   5. Write the relative position of the elements each group in the periodic table. This can be done by observing the periodic table.
      • Group a.
      • Group b.
      • Group c.
      • Group d.
   6. Give your own reason why these groups of elements are given the positions in the periodic table.
   7. Write down a summary or generalization about the classification of the elements in the periodic table.
   8. Let the representative of each group present their observations to the class.

      The whole class may discuss on the presentations, questions answers among students should be encouraged.

On the basis of students’ discussion, you can give the following explanations

• Those elements whose   valence electrons fall in the s-orbital are called s-block elements. Ask them in which group they are?
• Elements with valence electrons in the p-orbital are called p-block elements. Ask them which group elements they are?
• The s and p block elements are collectively called representative elements or main group elements. The groups are represented by roman numbers followed by letter A. These are groups IA to VIIA
• Elements whose valence electrons enter the d- orbital are called d-block and those with the last electron in f-orbital are f-block.
• The d-blocks are called transition elements because they are located between the two representative groups of elements.
• The f-block elements are called the rare earth metals because they are found rarely in nature.
• You may give further explanation on each block of the elements the next period.

Evaluation

Students can be asked the following oral questions to answer individually.

1. How many blocks does the modern periodic table have?
2. What is the basis to classify elements in the periodic table into blocks?
3. Identify the relative positions of each block in the periodic table.
4. What are the especial names of each group?

Encourage the slow learners to answer the above questions.

Concluding activity (9 minutes)

You can give the following concept map for the students as a concluding activity.
Fill the blank spaces in the concept map with the appropriate terms.

Make sure that students copied and completed the concept map successfully as follows.