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Unit One: Structure of the Atom

Lesson 4: The Quantum mechanical Model

Competencies 

Material:

  1. chart showing main energy level, sub-energy level, and maximum electron capacity ( table 1.5 on page 27 of student textbook)
  2. chart for sub-shell, number of orbital and maximum number of electrons

Starter Activity (8minutes)

You can start the lesson by revising Bohr’s electron configuration of main energy levels. Ask students:

Obviously students can answer most of the questions because they learned it in their grade 7 as well as in the previous lesson.

However, make sure that all students come to the consensus that according to Bohr:

Evaluation

Give them elements with atomic numbers of 11, 15 and 18 and ask them to write Bohr’s diagrammatic representation of the atoms.

Main Activities

You can use the following analogy to explain the quantum mechanical model. As you have residence address electrons in an atom also have systematic locations. As you can locate your address starting from Kebele to the bed on which you sleep, it is possible to determine position of an electron starting from atom to the volume of space it occupies.


Your address

Analogous location of an electron

Kebele

Atom

Home

Main energy level

Room in a home

Sub- energy level in a main energy level

Bed in a room

Orbital in sub-energy level

Direction of sleeping in a bed

Spin of an electron in an orbital

Now you can make students discuss with their partners by raising some questions.

Then use the chart to harmonize the discussion. As kebeles have different size so do the atoms. Small atoms have lower number of shells as small kebeles have lower number of houses.

Similarly, as houses of many family members, should have normally many rooms or sleeping places, shells or main energy levels of many electrons have many sub-shells or sub-energy levels as well.

Indeed as large rooms accommodate many beds and many people, larger sub-shells have many orbitals and hold many electrons.

Usually two persons (male and female) sleep in a bed.  Orbitals are also safe heavens for two electrons but can never hold more than two electrons. You may tell them humorously that when two persons sleep in a narrow bed, they sleep in opposite direction so that they can fit to the bed. Similarly, electrons always orient in opposite spin in an orbital.

Use the second chart to explain the sub-shell, number of orbitals and their maximum capacity.


Sub-shell/sub-energy level

Number of orbitals

Maximum number of electrons

s

1

2

p

3

6

d

5

10

f

7

14

Evaluation

You may give them the following individual work.

You may observe the works of each student and assist those who have difficulties.
Give opportunity for the students to ask questions. Let other students answer the forwarded questions.

Concluding Activity (8 minutes)

Explain how the quantum mechanical model modified the Bohr model?
Make sure that the slow learners are included in the lesson. Let them  respond to this question as follows: