1. Chem
Today: Bohr Diagrams, Waves, Energy
Next class: Flame Test Lab

2. Review: Bohr Model of the Atom
Electrons are shown in concentric shells or energy levels around the nucleus
The 1st shell can hold up to 2 electrons
The 2nd shell can hold up to 8 electrons
The 3rd shell can hold up to 18 electrons
The 4th shell can hold up to 32 electrons
When filling electrons, you fill the first (inner) shell first

3. Electrons
Valence electrons= electrons in the outermost shell of the atom

4. Lewis Structures (Electron Dot Diagrams)
A Lewis structure is in a sense a shortcut for representing the structure of an atom.
A Lewis structure contains 2 parts
1. element symbol (representing the nucleus)
2. electron dots (representing the valence electrons)

5. Lewis Structure Example
N has 5 valence electrons, so it’s Lewis structure would look like:
Maximum 2 electrons per side!
Note: by convention, you should not have more than 2 electrons per “side”
The maximum number of valence electrons you can have is 8.

6. Bohr Diagram Practice: Get stamped!
Use the example to help you fill out the Bohr Diagrams, Electron Configuration, and Valence Electrons

7. What do these 6 items all have in common?

8. Electromagnetic radiation
- a form of energy that has wavelike properties
- all forms found in the electromagnetic spectrum
Examples of electromagnetic radiation:
Xrays
Microwaves
Light waves
Radio waves – when you hear static on the radio when you aren’t getting a signal, that is the leftover microwaves from the big bang 15 billion years ago (it is cooling off so now the waves are the energy and wavelength of radio waves)

9. ELECTROMAGNETIC RADIATION
RADIO
WAVES
MICRO-
WAVES
INFRARED
LIGHT
VISIBLE
LIGHT UV
LIGHT
X-RAYS
LOWEST
ENERGY
HIGHEST
ENERGY

10. Listening to music in the car using the radio
RADIO WAVES
Listening to music in the car using the radio

11. MICROWAVES
Making popcorn

12. Using the remote control
INFRARED LIGHT
Using the remote control

13. The blue color of the sky
VISIBLE LIGHT
The blue color of the sky

14. ULTRAVIOLET LIGHT
Using a tanning booth

15. X-RAYS
Checking to see if the
ankle was broken

17. WAVELENGTH AND FREQUENCY ARE TWO IMPORTANT PROPERTIES OF WAVES.
DIFFERENT FORMS OF EMR TRAVEL IN WAVES.
WAVELENGTH AND FREQUENCY ARE TWO IMPORTANT PROPERTIES OF WAVES.

18. Wave Characteristics Amplitude Wavelength Wavelength
2 sec
0 sec
Amplitude
Wavelength
Wavelength
Frequency
Amplitude
The shortest distance between two equivalent
Points (meters)
How many waves pass a certain point per sec. (s-1 OR Hz)
Wavelength – the shortest distance between two equivalent points on a wave
Frequency – how many wave pass a certain point per second
Amplitidude –the height of the wave from crest to origin
State: Light travels as photons; photons have no mass but have energy
The energy a photon has is based on the equation E = hv
Energy is directly proportional to the frequency. Frequency has a unit of Hz which is = 1 𝑠 or s-1 or per second.
Wavelength is also related to frequency; how many people know the speed of light? Yes, what is it? EA 3 x 108 m/s
The speed of light is a constant that is known. Speed of light is based on the speed it travels over time. Wavelength is in meters and frequency is per second, so c=vλ
The height of a wave from crest to origin

19. THE HIGHER THE FREQUENCY, THE SHORTER THE WAVELENGTH
FREQUENCY = THE NUMBER OF WAVES THAT PASS BY A FIXED POINT PER SECOND.
THE HIGHER THE FREQUENCY, THE
SHORTER THE WAVELENGTH

20. THE HIGHER THE FREQUENCY, THE HIGHER THE ENERGY
FREQUENCY = THE NUMBER OF WAVES THAT PASS BY A FIXED POINT PER SECOND.
THE HIGHER THE FREQUENCY, THE HIGHER THE ENERGY

21. THE HIGHER THE ENERGY, THE SHORTER (SMALLER) THE WAVELENGTH

22. Practice

23. Electrons and Energy Levels
Each electron has a distinct amount of energy that is related to the energy level (shell) it is in
Electrons with the lowest energy are found in the shell closest to the nucleus
Electrons with the highest energy are found in the shell furthest from the nucleus
The greater the distance from the nucleus, the greater the energy of the electron

24. Each energy level has a maximum number of electrons that it can hold
The smallest energy level (the one closest to the nucleus, the first) can hold 2 electrons.
The second energy level, can accommodate 8 electrons.
The third energy level, can accommodate 18 electrons.
The 4th energy level can accommodate 32 electrons
N e
1 2
2 8
3 18
4 32

25. HOW DOES A NEON SIGN WORK?
BECAUSE OF ELECTRONS

26. Ground vs. Excited State
Ground state=when the electrons occupy the lowest energy levels possible
Excited state=electrons are found in a higher energy level or shell (even when a lower energy levels is not completely full)

27. Ground and Excited State
When an electron gains energy, it jumps to a higher energy level or shell
This is a very unstable condition
We call this condition the excited state
Very rapidly, an electron in the excited state will lose energy and move back to a lower energy level or shell
When excited electrons fall from an excited state to a lower energy level, they release energy in the form of light

28. Ground  Excited State
Electron gains energy from heat, light, electricity
Electron “jumped” to a higher energy level (shell)

29. Excited  Ground State Electron releases energy in the form of light
Electron “falls” back and returns to ground state (normal position)

30. Bright Line Spectrum
Electrons falling from an excited state down to the ground state give off visible light
Different elements produce different colors of light or spectra
These spectra are unique for each element (just like a human fingerprint is unique to each person)

31. Demo