1. Chapter Two …continued
Electrons in Atoms

2. Bohr’s Model Why don’t the electrons fall into the nucleus?
Move like planets around the sun.
Circular orbits at different levels.
Amounts of energy separate one level from another.

3. Bohr’s Model
Nucleus
Electron
Orbit
Energy Levels

4. } Bohr’s Model Further away from the nucleus means higher energy.
There is no “in between” energy
Energy Levels
Fifth
Fourth
Third
Increasing energy
Second
First
Nucleus

5. The Quantum Mechanical Model
The atom is found inside a blurry “electron cloud”
area where there is a chance of finding an electron.

6. Evidence of Quantum Mechanical Model
The study of light led to the development of the quantum mechanical model.
Light is a kind of electromagnetic radiation.
Electromagnetic radiation includes many kinds of waves
All move at 3.00 x 108 m/s ( c)

7. Parts of a wave
Crest
Wavelength
Amplitude
Orgin
Trough

8. Parts of Wave Orgin - the base line of the energy.
Crest - high point on a wave
Trough - Low point on a wave
Amplitude - distance from origin to crest
Wavelength - distance from crest to crest
abbreviated l (Greek letter lambda).

9. Frequency
The number of waves that pass a given point per second.
Units are cycles/sec, or hertz (hz)
Abbreviated n the Greek letter nu
c = ln

10. Frequency and wavelength
Are inversely related
As one goes up, the other goes down.
Different frequencies of light are different colors of light.
Wide variety of frequencies
The whole range is called a spectrum

11. Low
Energy
High
Energy
Radiowaves
Microwaves
Infrared .
Ultra-violet
X-Rays
GammaRays
Low Frequency
High Frequency
Long Wavelength
Short Wavelength
Visible Light

12. How color tells us about atoms
Atomic Spectrum
How color tells us about atoms

13. Prism
White light is made up of all the colors of the visible spectrum.
Passing it through a prism separates it.

14. If the light is not white
By heating a gas with electricity we can get it to give off colors.
Passing this light through a prism does something different...

15. Atomic Spectrum Each element gives off its own characteristic colors.
Can be used to identify the atom.
Composition of stars.

16. Emission Spectra
These are called discontinuous spectra, or line spectra
unique to each element.
Light is given off, or emitted.

17. Energy and frequency (Honors)
E = hn
E is the energy of the photon
n is the frequency
h is Planck’s constant
h = x Joules sec.
Joule is the metric unit of Energy

18. Equations for Light
Only 2 equations
c = ln
E = hn
Plug and chug.

19. Examples
What is the wavelength of blue light with a frequency of 8.3 x 1015 hz?
What is the frequency of red light with a wavelength of 4.2 x 10-5 m?
What is the energy of a photon of each of the above?

20. An Explanation of Atomic Spectra

21. Where the Electron Starts
The energy level an electron starts from is called its ground state.

22. Changing the energy
Let’s look at a hydrogen atom

23. Changing the energy
Heat, electricity, or light can move the electron up energy levels

24. Changing the energy
As the electron falls back to ground state it gives the energy back as light

25. Changing the energy May fall down in steps
Each with a different energy

26. { { {

27. Ultraviolet
Visible
Infrared
Further they fall, more energy, higher frequency.
This is simplified
the orbitals also have different energies inside energy levels
All the electrons can move around.

28. Heisenberg Uncertainty Principle
It is impossible to know exactly the speed and velocity of a particle.
The better we know one, the less we know the other.
The act of measuring changes the properties.

29. More obvious with the very small
To measure where a electron is, we use light.
But the light moves the electron
And hitting the electron changes the frequency of the light.

30. After Before Photon changes wavelength Photon Moving Electron
Electron Changes velocity
Moving Electron