1. Chapter 5 Electrons in Atoms

2. Light and the Atom
Last we spoke, we went over the structure of the atom
What do you remember?
After Rutherford came up with his proposed model of the atom, more questions came up than were answered: Namely, where do those electrons go?
Oddly enough, it was light that showed the way for chemists

3. Light and the Atom Lithium and water Sodium and water
Sodium and water
Potassium and water

4. Analysis of the emitted light revealed that an elements chemical behavior is related to the arrangement of the electrons in its atoms.
But to understand this more, we need to know a little bit about light…

5. The Wave Nature of Light
Visible Light is a type of electromagnetic radiation: a form of energy that exhibits wavelike behavior as it travels through space.
Other examples of EM are x-rays, radio waves, and even gamma rays

6. Characteristics of waves
Wavelength (λ): Shortest distance between equal points on a continuous wave (i.e. crest to crest, trough to trough) UNIT: m, cm, nm, etc… (a metric distance)
Frequency (υ): The number of waves that pass a given point per second. Unit: Hertz (Hz) aka wave/sec.
Amplitude: Height of the wave from origin to crest or origin to trough.

7. Frequency

8. Electromagnetic Wave relationship
c= λυ c= the speed of light in a vacuum (3.00 X 108 m/s) λ= wavelength υ= frequency

9. Electromagnetic Spectrum
Visible light, however, only comprises a small portion of what’s called the electromagnetic spectrum
The EM spectrum includes all forms of electromagnetic radiation, with the only differences in the types of radiation being their frequencies and wavelengths.

10. Electromagnetic Spectrum

11. A Problem
Microwaves are used to cook food and transmit information. What is the wavelength that has a frequency of 3.44 x 109 Hz?

12. The Particle Nature of Light
The only problem with thinking light is a wave is that you’re wrong…part wrong.
Saying light moves as a wave does not explain how light interacts with matter.
It doesn’t explain why heated objects only emit certain frequencies
And it doesn’t explain why some metals emit electrons when certain lights are shown on them (The Photoelectric Effect)

13. The Quantum Concept
When an object is heated, it emits a glowing light.
As something gets hotter, it possesses a greater amount of energy and it will turn different colors. These different colors correspond to different frequencies and wavelengths.
The wave concept could not explain the emission of these different frequencies.

14. A Quantum
A German physicist, Max Planck studied the light emitted by heated objects.
He concluded that matter can gain or lose energy in small, specific amounts called quanta.
A quantum is the minimum amount of energy that can be gained or lost by an atom.

15. A Quantum
Planck’s work also led him to create a mathematical formula to describe the relationship between the energy of a quantum and the frequency of the emitted radiation.
Equantum= hυ
h = Planck’s constant X Js
υ= frequency
E= Energy

16. Light’s Dual Nature
The photoelectric effect is when electrons are emitted from a metal when certain frequencies (or higher) of light are shown on the surface.
This does not agree with the wave model.
All of these discrepancies needed an explanation

17. The Duality of Light
It was Albert Einstein who suggested light has a dual nature: it acts as both a wave and a particle.
You can think of light as a beam of bundles of energy call photons (a massless particle that carries a quantum of energy)
Einstein went on to propose this equation:
Ephoton= hυ

18. A Problem
Every object gets its color by reflecting a certain portion of incident light. The color is determined by the wavelength of the reflected photons, thus by their energy. What is the energy of a photon from the voilet protion of the sun’s light if it has a frequency of x 10 14Hz?

19. Atomic Emission Spectra
What does a prism do? How do neon signs work?
If you were to light up a neon sign and pass the light through a prism, what do you think would happen? How about a glass tube filled with argon gas, instead of neon.
Each element has it’s own specific atomic emission spectrum- a set of frequencies of the electromagnetic waves emitted by atoms of the element