1. Electrons in Atoms
2.2 Configurations, Lewis Dot Diagrams and the Electromagnetic Spectrum

2. Electrons In Motion Electrons are negative and the nucleus is positive
Why aren’t electrons pulled into the nucleus and held there?
(1 min) Brainstorm answer with your shoulder partner
List as many ideas as possible

3. Niels Bohr(1885-1962 Worked with Rutherford suggested:
Electrons have enough energy to keep them in constant motion

4. Bohr’s Explanation
Electrons have energy of motion that enables them to overcome the nucleus’s attractive forces
This explanation is called the planetary model
Experiments show that electrons occupy orbits with defined amounts of energy, not random amounts like satellites in orbit.

5. The Electromagnetic Spectrum
High voltage electricity can increase the energy of an electron
Electromagnetic radiation or radiant energy can also supply energy to electrons
Electromagnetic radiation travels in waves with both electric and magnetic properties
Example: Radiant energy from the sun

6. Properties of Waves Frequency: number of wave vibrations per second
Unit of measure is hertz (Hz)
Wavelength: The distance between corresponding points on two consecutive waves

7. Relationship Between Frequency and Wavelength
A low frequency results in a long wavelength

8. Waves and Energy Waves transfer energy from one place to another
Electromagnetic waves have similar characteristics
However, they can travel through empty space
Ex. Radio waves
Microwave radiation
Visible light
All of these forms of radiant energy are part of the electromagnetic spectrum

10. Visible light
Is a very small portion of the spectrum

11. Answer the Following:
What form of electromagnetic radiation in this diagram has the longest wavelengths?
What wavelengths do microwaves have?
What is the unit of wavelengths?
What form of electromagnetic radiation in this diagram has the highest energy?

12. Answers Radio Waves (10-100,000 nm) 0.010-1.0 nm Nm (nanometers)
Gamma rays ( Hertz)
Higher frequency has higher energy and shorter wavelength

13. Aurora Borealis : Northern Lights
What causes these lights?
Caused by Solar Winds: A continuous flow of electrons and protons from the sun
High-energy charged particles collide with oxygen and nitrogen in the ionosphere transferring energy to them
The increased energy causes the electrons to jump to higher energy levels
When the electrons return to the lower energy level they release the energy as light
The amount and location of the energy released determines the visible color

14. Aurora and Atomic Structure
How does the aurora borealis relate to the structure of an atom?
Excited electrons dropping to lower energy levels produces the different colored lights
This supports the model of the atom having electrons in specific energy levels
The colors are predictable based on those produced by electrons in specific gasses which make up the atmosphere.

15. Electrons and Light
What does the electromagnetic spectrum have to do with electrons?
It is related to the energy of motion of electrons and radiant energy- different amounts of energy released cause diff. colors

16. Analogy: Book Drop
Rank the heights of the drop based on the sound produced by the fall
Close your eyes and listen carefully
Which fell from the greatest height?
Which fell from the lowest height?
How could you tell?
How does this relate to electron energy and the light?

17. Emission Spectrum
Emission Spectrum: the spectrum of light released from excited atoms of an element
Each element has its own, different, emission spectrum
It is like a fingerprint.
Evidence of energy levels:
Electrons absorb only enough energy needed to move to a specific higher energy level
When falling back they give off only the amount of energy to drop them back to that lower energy: giving off a specific color of light.

18. Electrons Moving to Different Energy Levels

19. Electrons and Energy Levels
Like your feet on a ladder, electrons can not be between energy levels
They must absorb the amount of energy required to land on an energy level
However, energy levels are not evenly spaced like rungs on a ladder.
As n increases the energy levels get closer together

20. Line Emission Spectra Lab
Silently Read the lab Background information
Note any questions that arise AS YOU READ.
Mark the text
Propose a question to investigate, during the lab, by looking at various spectra

21. Your Hypothesis Construct a hypothesis
An if then statement which connects the independent variable (the one you change) to the dependent variable (the one you can not change)
Example: If I lower the temperature of the room to 20 degrees for the next 24 hours, then all of my plants will freeze.
If _____________________________________ then_____________________________.

22. Your Experiment
How will you make your observations in order to answer your question and test your hypothesis?
Note the material available on the table.
Write specific instructions in your “Experiment” Section, be sure to say what you will do, what you will write down and how you will record your observations/data
First……..
Second…..
Then……

23. Submit your plan for approval
Once you have received approval, carefully conduct your experiment.
Prepare your poster presentation
Be sure to include all of the required components, from the lab handout.
Share your poster, when assigned

24. Poster Presentations

25. The Electron Cloud
Continuing research has shown that energy levels are not neat
They are regions of space around the nucleus in which electrons are most likely to be found
The space around the nucleus where the atom’s electrons are most likely to be found is called the Electron Cloud

26. Electron In Energy Levels
The lowest energy level is the smallest and closest to the nucleus
One S suborbital with one orbital =2electrons
The 2nd energy level is larger, holds 8 electrons
One P suborbital with 3 orbitals = 6 electrons
The 3rd energy level is even larger and further away from the nucleus, holds 18 electrons
One D suborbital with 5 orbitals = 10 electrons

27. Valence Electrons
Electrons in the outermost or highest energy level are called valence electrons
Many physical and chemical properties of an element are directly related to the number and arrangement of valence electrons
Valence electrons are the ones that interact during a chemical reaction

28. Lewis Dot Diagrams
Because valence electrons are very important to the behavior of atoms, we represent them is symbols
Lewis Dot Diagrams represent VALENCE electrons as dots around the chemical symbol of the element
Each dot represents 1 valence electron

29. Writing Lewis Dot Diagrams
Helium
Has 2 valence electrons, so 2 dots
He: This is the Lewis Dot Diagram for Helium
You try one:
Write the Lewis Dot Diagram for Oxygen.

30. Assessment
For each of the following elements, describe how many electrons are in each energy level, and draw the Lewis Dot Diagram
Argon
Magnesium
Nitrogen
Aluminum
Explain the change that occurs within an atom when it emits light
Explain the differences and similarities between Bohr’s model of the atom and the electron cloud model.
Describe how we concluded that electrons occupy specific energy levels.
Use an everyday example to prove that light waves transfer energy

31. Answers
2,8,8
2,5
Mg: ,8,2
Al: ,8,3
Electrons absorb energy and jump to higher energy levels. Then electron drops down to lower level again, they give off the energy as light.
Cloud- region of high probability of finding electron
Bohr- specific, neat orbits BOTH show e- in orbit
3. Atoms release energy of only certain frequencies, so certain energy levels are given off, so electrons must be in only certain frequencies
4.Photovaltaic cells, things in the light get warm, heat lights