Beacon Lesson Plan Library

Order, Order All Electrons

Rosemary Wilson
Santa Rosa District Schools

Description

Students learn how to ‘read' the periodic table by applying their knowledge of the construction of atoms. Applications of Aufbau Principle, Hund's Rule, and Pauli Exclusion Principle will be explained in detail.

Objectives

The student knows that elements are arranged into groups and families based on similarities in electron structure and that their physical and chemical properties can be predicted.

Materials

-Periodic Table Wall Chart
-Textbook of choice
-Laser pointer
-Blackboard and chalk or overhead, transparency
and marking pen
-Handout showing four-story building with divisions
for types of apartments
-Handout showing energy level diagram for entering
electrons

Preparations

1. Draw element ‘building’ on the blackboard or on a transparency.
2. Draw energy level diagram on the blackboard or on a transparency.
3. Check batteries in laser pointer.
4. Prepare ‘building’ handout showing a four-story building with ‘s’, ‘p’, ‘d’, and ‘f’ apartments when they arise.
5. Prepare energy level for entering electrons handout showing ‘d’ electrons actually one level below the expected entry and ‘f’ electrons actually two levels below the expected entry.

Procedures

1. It is imperative to define Aufbau Principle, Hund’s Rule and Pauli Exclusion Principle before beginning this lesson so that students already have those concepts explained as far as their limited knowledge will allow. Students also need to have prior knowledge of the use of symbols for elements and the make-up of atoms confined to electrons, protons and neutrons. They should also be taught that there are four types of ‘orbitals’ for electrons called ‘s’, ‘p’, ‘d’, and ‘f’ and that these orbitals will be individually filled before another orbital type is started. The students should have already been taught limited knowledge of quantum numbers so that they know that a pair of electrons in an orbital are illustrated by two arrows, one going up and one going down.

2. Explain to the students the importance of the periodic table in that it holds a wealth of information if they only learn to ‘read’ it.

3. Ask the students as a whole, if anyone has an idea as to the arrangement of the symbols of the elements on the periodic table or could it be that it is just arranged that way because of convention.

4. After students give suppositions as to the arrangement, explain that an atom is like a building having apartments which are 1, 3, 5 or 7 bedroom apartments having the limitation of double occupancy.

5. Draw a diagram on the board, or have one prepared for the overhead, which already shows, or will eventually show, a tall building with four floors. Refer to the handout which shows the building with the floors divided into ‘s’, ‘p’, ‘d’, and ‘f’ apartments.

6. Explain to the students that you cannot reach the second floor without first going on the first floor (Aufbau Principle).

7. Explain to the students that the first floor only has one type of apartment, an ‘s’ type which is only a one bedroom apartment. As soon as it is clear that there is only one apartment with one bedroom on the first floor, explain to the students that there is a maximum of ‘double occupancy’ allowed in each bedroom (Pauli Exclusion Principle). As soon as the first floor is explained, ask a student how ‘many elements’ should be on the first floor since there is only one type of apartment and there is only one bedroom in that type of apartment.

8. The student should answer ‘2’. Using the laser pointer, highlight the first floor, period, on the periodic table wall chart, and ask the class how many element’s symbols are on the first floor. The answer should be ‘2’.

9. Next, draw the second floor with two types of apartments available, ‘s’ and ‘p’. Explain that there is still just one ‘s’ which has ‘double occupancy but there are three ‘p’ apartments each having ‘double occupancy’.
10. Ask a student how many elements should be allowed on the second floor considering the ones’ with double occupancy and the three ‘p’s with double occupancy.

11. The answer should be ‘8’. Using the laser pointer, highlight the second floor, period, on the wall chart and ask the students how many elements are actually on the second floor. There are ‘8’.

12. ( Before continuing with the third floor, it is advisable to determine the ability of the class to comprehend deviations in the chart which can be explained but sometimes serve to confuse the more challenged student.) For the third floor, explain that there are three types of apartments available, ‘s’, ‘p’ and ‘d’. The ‘s’ type apartment still has only one bedroom, the ‘p’ type has three bedrooms but the ‘d’ type has five bedrooms. Explain that there is still a maximum of ‘double occupancy’ for each bedroom. Ask a student how many elements should be on the third floor considering there is an ‘s’ with one bedroom having two occupants, a ‘p’ with three bedrooms having two occupants each and a ‘d’ with five bedrooms having two occupants each. The answer should be ‘18’.

13. With the laser pointer, highlight the third floor, period, of the periodic table and ask the students how many elements' symbols are on the third floor. Unfortunately, the answer is ‘8’. Now explain the entering of electrons into the lowest energy level available, Hund’s Rule.

14. Using a second diagram on the blackboard or the overhead, show an energy level diagram showing the overlapping of the third and fourth floors such that the ‘s’ electrons on the fourth level are actually lower in energy than the ‘d’ electrons on the third floor. Refer the students to their handout showing the energy levels of entering electrons.

15. Using the laser pointer, highlight the fourth floor. Show that the first two elements are those 4 ‘s’ electrons which fill before the 3 ‘d’ electrons. Ask a student if it is visible anywhere on the chart where there might be an area of grouping of 10 elements which are set apart from the others. The answer should be that there are 10 symbols immediately after the two elements which have 4 ‘s’ electrons.

16. Explain to the students now that the ‘d’ electrons are always located on one level below where they should be but that they are still 3 ’d’ electrons not 4 ’d’ electrons.

17. Explain to the students that the fourth floor has four types of apartments, ‘s’, ‘p’, ‘d’, and ‘f’. Explain that the ‘s’ still has one bedroom, the ‘p’ still has three bedrooms, the ‘d’ still has five bedrooms. Ask how many bedrooms they think an ‘f’ apartment might have. Place the numbers 1 – 3 – 5 - ? on the board to help the students see the sequence. The answer should be ‘7’. Ask how many elements' symbols should be found in an area if there is ‘double occupancy’ for each bedroom. The answer should be ‘14’.

18. Ask a student if there is an area they see on the chart which has ‘14’ element’s symbols which are isolated as a group. Using the laser pointer, highlight the ‘f’ block.

19. At this time, the question usually arises which ponders why the ‘f’ block elements are below all the others on the chart and why they are not placed at the point of entry as the ‘d’ elements are. Explain that this is a possibility but that the chart would be too wide and that this is convention to place them below the others since it is their understood point of entry.

20. Using the laser pointer as you ‘read’, choose an element’s symbol on the periodic table and ‘read’ its electron configuration by reading from left to right, top to bottom, now knowing to read the period level, 1, 2, 3, etc., and the orbital type, ‘s’, ‘p’, ‘d’, or ‘f’, showing the students ‘reading’ the chart simply by knowing how it is built. When ‘reading’ the configuration, use superscripts after the orbital type to show how many electrons are in that section, eg. 1 s2, 2 s2, 2 p6, 3 s2, 3 p3 for P. Choose a second example for reinforcement.

21. Ask the class for a volunteer to choose an element and ‘read’ aloud its electron configuration simply by looking at the periodic table wall chart. Help the other students follow what the volunteer is ‘reading’ by using the laser pointer to highlight the areas being read by the volunteer as he/she proceeds.

22. If a student is incorrect in the configuration, allow that student to try again after being given restated information which is needed for that student to correct the error.

23. After the student volunteer has ‘read’ aloud the electron configuration of the chosen element, write the configuration on the blackboard or the overhead for the students to see the placement of each item read, eg. 2 s2.

24. Choose one of the examples placed on the board to show the students that if you add the superscripts of all the orbitals, the number will be the same as the atomic number of that element.

25. Repeat the ‘reading’ of configurations by volunteers as time allows. Repeat the correction process for ‘reading’ configurations if necessary.

26. Sum all points covered before assessing students;
Aufbau Principle
Pauli Exclusion Principle
Hund’s Rule‘
s’, ‘p’, ‘d’, ‘f’ orbitals

27. Final step for students to show mastery of the reading of the periodic table as it relates to electron configuration is to ask them to write the configurations of the five elements listed on the ‘Electron Building’ handout.

Assessments

Note: This lecture has an informal formative assessment imbedded throughout the lecture process .

1. Ask a student to determine an element’s electron configuration by ‘reading’ the periodic table for a specific element.
2. Continue to ask students to determine other elements' electron configurations by choosing specific students or by taking volunteers.
3. Direct the students to write the electron configurations of two elements, Al and Se, on the backs of the ‘building’ handout using the proper format as read from the periodic table. (i.e. 1 s 2, 2s2, 2p6 etc.)
4. Students will show achievement when they successfully ‘read’ the periodic table by writing the electron configurations of the two example elements.
5. Understanding of this knowledge will be addressed on the written test for the chapter.
6. Goal 3 objective is assessed by the students’ abilities to ‘read’ the periodic table as to its indication of electrons’ entry order.

Extensions

1. Students need to have the basic knowledge of chemistry which should be covered in preceding chapters of any traditionally organized chemistry textbook.
2. Continue this information to show that the properties of elements can be predicted because of the placement on the periodic table and that this is due to electron arrangement.
3. Enhance this information by explaining the brilliant work of Dimitri Mendeleev and his formulation of the early periodic table. Also mention the works of other scientist who were also trying to discover a logical arrangement of elements and their characteristics and properties, eg. Newlands.
4. Show related films such as The Periodic Table and Periodicity.

Web Links

Web supplement for Order, Order All Electrons
Chemical Elements

Return to the Beacon Lesson Plan Library.