1. Modern Atomic Model

2. Electron modeling…
To understand electrons, scientists began comparing them to something they knew - light.

3. What they knew about light
Light is a wave – similar to water waves
Visible light belongs to electromagnetic radiation spectrum
Origin - 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

4. Behavior of light All forms of EMR have common properties: Amplitude
Wavelength
Frequency
Speed
1- electric & magnetic field right angles to each other
2- gamma rays [10-11], X-rays [10-9], UV [10-8], visible spectrum (ROYGBV) [4.00 x 10-7 – 7.00 x 10-7], IR [10-6], microwave [10-2], TV [100], radio [101]
3 - IR longer than visible spectrum wavelengths, is radiant heat, Microwaves longer still (heat only food by transferring E to moisture in food), Short waves on other side of visible light (UV  sunburn & skin cancer)
4 - When we say light, we are talking about visible light.

5. Behavior of Light
Wavelength (l), frequency (n), and speed (c) are mathematically related
c = ln

6. Behavior of light Frequency and wavelength: Are inversely related
As one goes up, the other goes down.
Different frequencies of light go with different colors of light.
There is a wide variety of frequencies
The whole range is called a continuous spectrum

7. Continuous EMR Spectrum
Radiowaves
Microwaves
Infrared .
Ultra-violet
X-Rays
GammaRays
Low Frequency
High Frequency
Long Wavelength
Short Wavelength
Visible Light

8. Wave model had problems
At the start of the 20th century, scientists made observations of light that didn’t fit the model…

9. Wave model problems Black body radiation
In 1900, Max Planck heated matter that didn’t burn and studied the radiation emitted. It was predicted that matter could absorb or emit any quantity of energy. His experimental data did not fit that statement.

10. What happened to the rest of the light?
Max Planck
What happened to the rest of the light?

11. E = h Wave model problems
Based on Planck’s work, we know the following about light:
The energy is in specific amounts called quanta.
The light’s energy (E) and frequency (n) are directly related by a constant (h).
E = h
E = h x nu
E is the energy of the photon
nu is the frequency
h is Planck’s constant and equals x Joules × seconds

12. Wave model problems
Planck’s ideas weren’t accepted until some time later when Albert Einstein used Planck’s equation to work on solving the photoelectric effect.

13. Wave model problems  Photoelectric effect
Light shining on certain metals can eject electrons.
Simulation
Ex. an intense light w/low frequency could shine all day w/o knocking out any electrons
The fact that light was able to knock electrons loose wasn’t a problem. What wave theory couldn’t explain was why only certain frequencies of light (or higher) could knock out electrons.

14. Wave model problems
Which has greater energy – red or violet light?

15. Wave model problems  Photoelectric effect
Einstein proposed that light consisted of energy quanta that behaved as particles – not waves. He called them photons instead of quanta.
The problem was then solved by the notion that radiation is emitted or absorbed in whole numbers of photons.
Electrons need specific energy photon, not several photons of any energy. Higher energy comes from light with higher frequencies [smaller wavelengths]. Higher energy is also associated with damage to organisms [X-rays…]

16. Wave model problems  Photoelectric effect
It was later proven that light could definitely act as a particle. So, we now have light acting as both a wave and a particle.
This will be the basis for understanding how e- behave.

17. Wave model problems  Bright line spectrum
Scientists noticed that you could vaporize an element in a flame to produce different flame colors. You can then use a prism to sort the colors to produce a line spectrum (only certain colors are produced).

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

19. If the light entering the prism is not white…
By adding energy to a gas, we can get the gas to give off colored light
Passing this light through a prism does something different than white light

20. Wave model problems  Bright line spectrum
Problem: Each element produced a different line spectrum.

21. These are called line spectra They are unique to each element.
These are emission spectra (the light is emitted or given off)
Each element gives off its own characteristic colors
*Can be used to identify the element
*How we know what stars are made of

22. Rutherford’s Model
Doesn’t work to help explain the bright line spectrum – we need something better

23. Bohr’s Model: An explanation for the observed atomic spectra

24. Bohr Model for Hydrogen
The e- goes around the nucleus only in allowed paths called orbits.
The H atom has energy possibilities based on which orbit the e- occupies.
The ground state occurs when the e- is in the orbit closest to the nucleus.
The orbit containing the e- determines the outer dimensions of the atom.
The energy of the e- increases as it moves to orbits that are farther from the nucleus (excited state).

25. Bohr’s Model simplified}
Energy is in Levels
Further away from the nucleus means more energy.
There is no “in between” energy
Fifth
Fourth
Increasing energy
Third
Second
The different possible orbits in the H atom can be visualized in the following analogy. [ladder analogy – When on a ladder, you have to stand on the rungs. You can’t stand halfway in between the rungs. For each rung, there is a set amount of potential energy. So, the distance between the rungs can be used to explain the gain or loss of E ( = gain,  = loss).] An e- can only be in an orbit, it can’t be between orbits.
First
Nucleus

26. Picture the Loss and Gain of Energy for an e-
Higher Energy Level or excited state
Light Energy G a I n
Loss
Summary: The electron went from particle to wave and back!
*The farther the electrons fall, the more energy released and higher frequency produced
*All the electrons can move
Lower Energy Level or ground state

27. Bohr Model - Explains where an electron is most likely to be found
The first shell is lowest in energy
2nd level next
Electrons occupy shells in order
They are numbered: 1, 2, 3, 4, 5, 6 etc
Nucleus
Then 4th
Then 3rd

28. Energy input will determine which level the electron moves to
Jumps and Lines
Energy Hydrogen Spectrum
410
434
486
656
Energy
Energy
Nucleus
Energy input will determine which level the electron moves to
Nucleus

29. Energy input will determine which level the electron moves to
Jumps and Lines
Energy Helium Spectrum
447
501
587
667
Note that these are different frequencies from H
Every element is unique!
Energy
Energy
Nucleus
Energy input will determine which level the electron moves to
Nucleus
Ideas are the same. The second electron effects the atomic structure and therefore the spectrum.

30. Bohr Model Problems Unfortunately, Bohr’s model only worked for H.
So what about the 100+ other elements?

31. Matter exhibits both wave and particle properties!
De Broglie
Determined that particles of matter could act as waves.
Described the wavelength of moving particles.
Conclusion:
Matter exhibits both wave and particle properties!
For that matter, all matter is able to act as a wave. The problem w/ things bigger than atoms is that the wavelength is too small to be detected.