1. Chapter 5
Electrons In Atoms

2. Topics to Be Covered 5.1 5.2 5.3 Light and Quantized Energy 136-145
Quantum Theory and the Atom
5.3
Electron Configuration

3. Light and Quantized Energy
Section 5.1
Light and Quantized Energy

4. The Atom & Unanswered Questions
Early 1900s
Discovered 3 subatomic particles
Continued quest to understand atomic structure
Rutherford’s model
Positive charge in nucleus
Fast moving electrons around that
No accounting for differences and similarities in chemical behavior

5. The Atom and Unanswered Questions
Example:
Lithium, sodium, and potassium have similar chemical behaviors (explained more in next chapter)
Early 1900s
Scientists began to unravel mystery
Certain elements emitted visible light when heated in a flame
Analysis revealed chemical behavior depends on arrangement of electrons

6. The Wave Nature of Light
Electromagnetic radiation
A form of energy that exhibits wavelike behavior as it travels through space
Visible light is a type of ER

7. Characteristics of Waves
All waves can be described by several characteristics
Wavelength
Frequency
Amplitude

8. Wavelength Represented by lambda λ
Shortest distance between equivalent points on a continuous waves
Measure crest to crest or trough to trough
Usually expressed in m, cm, or nm

9. Frequency Represented by nu ν
The number of waves that pass a given point per second
Given in the unit of hertz (Hz)
1 Hz = 1 wave per second

10. Amplitude
The wave’s height from the origin to a crest or from the origin to a trough
Wavelength and frequency do not affect amplitude

11. Speed
All electromagnetic waves in a vacuum travel at a speed of 3.00 x 108 m/s
This includes visible light
The speed of light has its own symbol C
C= λν

12. Electromagnetic Spectrum
Also called the EM spectrum
Includes all forms of electromagnetic radiation
With the only differences in the types of radiation being their frequencies and wavelengths

13. Electromagnetic Spectrum
Figure 5.5

14. Problems
Page 140
Calculating Wavelength of an EM Wave

15. Particle Nature of Light
Needed to explain other properties of light
Heated objects emit only certain frequencies of light at a given temperature
Some metals emit electrons when light of a specific frequency shines on them

16. Quantum Concept When objects are heated they emit glowing light 1900
Max Planck began searching for an explanation
Studied the light emitted by heated objects
Startling conclusion

17. Quantum Concept Planck discovered:
Matter can gain or lose energy only in small specific amounts
These amounts are called quanta
Quantum—is the minimum amount of energy that can be gained or lost by an atom

18. Example Heating a cup of water
Most people thought that you can add any amount of thermal energy to the water by regulating the power and duration of the microwaves
In actuality, the temperature increases in infinitesimal steps as its molecules absorb quanta of energy, which appear to be a continuous manner

19. Quantum Concept
Planck proposed that energy emitted by hot objects was quantized
Planck further demonstrated mathematically that a relationship exists between energy of a quantum and a frequency

20. Energy of a Quantum Equantum=hv Equantum represents energy
h is Planck’s constant
v represents frequency

21. Planck’s Constant Symbol = h 6.626 x 10-34 J*s
J is the symbol for joule
The SI unit of energy
The equation shows that the energy of radiation increases as the radiation’s frequency, v, increases.

22. Planck’s Theory For given frequencies
Matter can emit/absorb energy only in whole number multiples of hv
1hv, 2hv, 3hv, 4hv etc.
Matter can have only certain amounts of energy
Quantities of energy between these values do not exist

23. The Photoelectric Effect
electrons, called photoelectrons
are emitted from a metal’s surface
when light of a certain frequency, or higher than a certain frequency shines on the surface

24. Light’s Dual Nature
Einstein proposed in 1905 that light has a dual nature
photon—a massless particle that carries a quantum of energy

25. Energy of a Photon Ephoton=hv Ephoton represents energy
h is Planck’s constant
v represents frequency

26. Light’s Dual Nature Einstein proposed
Energy of a photon must have a certain threshold value to cause the ejection of a photoelectron from the surface of a metal
Even small #s of photons with energy above the threshold value will cause the photoelectric effect
Einstein won Nobel Prize in Physics in 1921

27. Sample Problems Page 143 Sample Problem 5.2
Calculating Energy of a Photon

28. Atomic Emission Spectra
See page 145

29. Quantum Theory and The Atom
Section 5.2
Quantum Theory and The Atom

30. Bohr’s Model of the Atom
Dual-nature explains more
Atomic Emission Spectra
Not continuous
Only certain frequencies of light
Explained the Atomic Emission Spectra

31. Energy States of Hydrogen
Bohr proposed certain allowable energy states
Bohr proposed electrons could travel in certain orbitals

32. Energy states of Hydrogen
Ground State
Lowest allowable energy state of an atom
Orbit size
Smaller the orbit, the lower the energy state/level
Larger the orbit, the higher the energy state/level

33. Energy states of Hydrogen
Hydrogen can have many excited states
It only has one electron
Quantum Number
Number assigned to each orbital n
Look at Table 5.1

34. The Hydrogen Line Spectrum
Hydrogen Ground State
Electron is in n=1 orbit
Does not radiate energy
Hydrogen Excited State
Energy is added to the atom from outside source
Electron moves to a higher energy orbit

35. The Hydrogen Line Spectrum
Only Certain Atomic Energy Levels Possible
Example Our Classroom
Balmer Series
Electron transitions from higher-energy orbits to the second orbit
Account for visible lines

36. The Hydrogen Line Spectrum
Lyman Series
Ultraviolet
Electrons drop into n=1 orbit
Paschen Series
Infrared
Electrons drop into n = 3 orbit