1. Chapter 5: Electrons in Atoms

2. Why focus on electrons?
Scientists wanted to know why certain elements behaved similarly to some elements and differently to others
Reactivity
When heated with a flame

3. Light as Waves Visible light is a type of electromagnetic radiation
electromagnetic radiation - a form of energy that exhibits wavelike behavior as it travels through space

4. Wave Diagram

5. Frequency (υ/f) - number of waves per second
- in hertz (Hz) or s-1 or 1 𝑠
Wavelength (λ) - distance between corresponding parts on consecutive waves
- in meters (m)
Speed of light (c)
x 108 m/s

6. Electromagnetic Spectrum
HIGH
ENERGY
LOW
ENERGY
Raging Martians Invaded Venus Using X-Ray Guns

7. c = f Frequency and wavelength are INVERSELY related
- as one goes up, the other goes down
c = f
c: speed of light (3.00  108 m/s)
: wavelength (m, nm, etc.)
f: frequency (Hz)

8. What is the frequency of light that has a wavelength of 680. nm?

9. What is the wavelength of light with a frequency of 4.27 x1018 hertz?

10. Turn to your partner and summarize…
State the relationship between the energy and frequency of electromagnetic radiation.
Answer: frequency and energy are directly related, when one goes up, the other goes up, too
What are the only differences between the types of electromagnetic radiation on the electromagnetic spectrum?
Answer: frequencies and wavelengths of the waves

11. Light as Particles
In the early 1900’s, German physicist Max Planck was trying to understand why some substances change color when heated.

12. What Max thought
As the substance is heated, its energy changes in specific amounts called quanta
Quantum: the minimum amount of energy that can be gained or lost by an atom
The amount of energy that can be emitted by a substance is directly proportional to the frequency of the radiation given off.
If something is heated, the energy is increased and different frequencies of light are given off (different colors).

13. Ground state: the lowest allowed energy state of an atom or other particle

14. Einstein’s Contribution
Observed the photoelectric effect
Concluded - light has properties of both waves and particles
“wave-particle duality”
Photon - particle of light that carries a quantum of energy
C. Johannesson

15. The Photoelectric Effect
Electrons (called photoelectrons) are emitted from a metals surface when light of a certain frequency shines on the surface

16. E = hf Energy of light is:
- directly related to the frequency of the light
- inversely related to the wavelength.
- As frequency , energy
- As wavelength , energy
Energy has units of Joules (J)
h = Planck’s constant = x J. s
E = hf

17. A photon has an energy of 1. 23 x10-16 J
A photon has an energy of 1.23 x10-16 J. What is the frequency and wavelength of the photon?

18. What is the energy and wavelength of radiation whose frequency is 6
What is the energy and wavelength of radiation whose frequency is x 1018 hertz?
3.00 x108 m/s = 4.44 x10-11 m
6.775 x1018 s-1
E = h υ = (6.626 x10-34 Js) (6.775 x1018 s-1)
= x10-15 J
λ = 𝑐 υ

19. What is the wavelength of light that has a frequency of 2
What is the wavelength of light that has a frequency of 2.27 x1017 hertz?
What is the frequency of light that has a wavelength of 680. nm?
What is the wavelength of light with a frequency of 4.27 x1018 hertz?
A photon has an energy of 1.23 x10-16 J. What is the frequency and wavelength of the photon?

20. wavelength = 1.32 x10-9 m
frequency = 3.29 x1017 hertz
wavelength = 7.03 x10-11 m
frequency = 1.86 x1017 hertz
wavelength = 1.62 x10-9 m

21. So what does light have to do with chemistry?
You can identify an element by the color of light it gives off when heated…

22. How is light given off?
When atoms absorb energy (for example, from a flame), electrons become excited and temporarily get into a higher energy level
When they drop back down to their ground state, energy is released in the form of light
Atomic emission spectrum: the set of frequencies of the electromagnetic spectrum that consists of several individual lines of color corresponding to the frequencies of the radiation emitted by atoms of the element