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Electrons in Atoms
Section 5.1 Light and Quantized Energy
Section 5.2 Quantum Theory and the Atom
Section 5.3 Electron Configuration
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3. Section 5.1 Light and Quantized Energy
Compare the wave and particle natures of light.
Define a quantum of energy, and explain how it is related to an energy change of matter.
Contrast continuous electromagnetic spectra and atomic emission spectra.
radiation: the rays and particles —alpha particles, beta particles, and gamma rays—that are emitted by radioactive material
Section 5-1

4. Section 5.1 Light and Quantized Energy (cont.)
electromagnetic radiation
wavelength
frequency
amplitude
electromagnetic spectrum
quantum
Planck's constant
photoelectric effect
photon
atomic emission spectrum
Light, a form of electronic radiation, has characteristics of both a wave and a particle.
Section 5-1

5. The Atom and Unanswered Questions
In Rutherford's model, the atom’s mass is concentrated in the nucleus and electrons move around it.
The model doesn’t explain how the electrons were arranged around the nucleus.
The model also doesn’t explain why negatively charged electrons aren’t pulled into the positively charged nucleus.
Section 5-1

6. The Atom and Unanswered Questions (cont.)
Li, Na, K: same column (group or family) on periodic table
Are metals
React with water to form hydrogen gas
In the early 1900s, scientists observed certain elements emitted visible light when heated in a flame.
Analysis of the emitted light revealed that an element’s chemical behavior is related to the arrangement of the electrons in its atoms.
Section 5-1

7. The Wave Nature of Light
electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space.
Visible light is a type of electromagnetic radiation (other types: radio waves, microwaves, infrared radiation, ultraviolet radiation, X-rays, and gamma rays)
Section 5-1

8. Characteristics of waves
The wavelength (λ – Greek letter lambda) is the shortest distance between equivalent points on a continuous wave. It is usually measured from crest to crest. Units are meters (m)
The frequency (n – Greek letter nu) is the number of waves that pass a given point per second. Units are:
wave/second, 1/s, s-1 or Hertz (Hz)
The amplitude ( - Greek letter psi) is the wave’s height from the origin to a crest.
Section 5-1

9. All EM (electromagnetic) radiation travels at the speed of light
The speed of light in a vacuum is x 108 m/s
3.00 x 108 m/s x 1km/1000m x mile/1km = 186,390 miles/s which rounds to 186,000 miles/s
3.00 x 108 m/s = 186,000 miles/s

10. The Wave Nature of Light (cont.)
The crest is the top of the wave; the trough is the bottom of the wave
Section 5-1

11. Red has longest wavelength; shortest frequency
Violet has the shortest wavelength; highest frequency

12. Figure 7.1 The Nature of Waves
Comparing red, green, blue waves. The larger the wavelength, the lower the frequency.

13. Spectroscopy
Spectroscopy is a term that describes lab methods of exposing substances to some sort of continuous energy. .

14. This enables a scientist to analyze the “spectrum” produced
This enables a scientist to analyze the “spectrum” produced. This spectrum acts like a fingerprint for the substance and this fingerprint can identify the substance to a knowledgeable person

15. How Spectroscopy works
A normal atom, unexposed to energy, is said to be in its ground state, which is the most stable state of the atom.
When the atom is exposed to energy, it is said to be in an excited state, where one or more e- have jumped to higher energy levels.

16. As the atom goes from ground state to excited state, it absorbs energy, so the spectrum produced is called an absorption spectrum.
As the atom goes from the excited state back to ground, it emits energy, thus the spectrum produced is an emission spectrum.

17. Note differences in spectra:
Continuous has no lines
Emission shows colored lines against a dark background
Absorption shows lines that are an absence of color against a continuous spectrum
Each set of lines is a fingerprint that would identify an element

18. A spectrum is a pattern studied in spectroscopy
A spectrum is a pattern studied in spectroscopy. A spectrum may also be defined as “a series of wavelengths”.

19. The Wave Nature of Light (cont.)
The electromagnetic spectrum is a list of all forms of electromagnetic radiation. Visible light (colors we see) lies in the middle of the whole spectrum.
Section 5-1

20. The Wave Nature of Light (cont.)
Note: the color you see is the color reflected from white light; all others are absorbed.
For example: if you see green, green is reflected and ROYBIV are absorbed. White reflects all; black absorbs all
Section 5-1

21. other
A prism can separate sunlight into a continuous spectrum of colors.
Sunlight is a continuous range of wavelengths and frequencies. It is “visible light”.

22. White is all colors of visible light reflected back
Black is all colors of visible light absorbed
A color is what gets reflected, all others get absorbed
Ex: green means green is reflected and ROYBIV are absorbed

23. An oscilloscope is an instrument that allows you to see waves.

24. Figure 7.2 Classification of Electromagnetic Radiation

25. All EM radiation travels at the same speed, that is, the speed of light (c)
c = 3.00 x 108 m/s

26. c is the speed of light (3.00 x 108 m/s)
Equation to memorize:
c = ln
c is the speed of light (3.00 x 108 m/s)
l is wavelength measured in meters
n is frequency measured in 1/s
Wavelength(l) and frequency (n ) are inversely proportional to each other; that is, as one goes up, the other goes down.

27. This diagram shows that as frequency goes up, the wavelength gets shorter.

28. Example: What would be the wavelength of radiation coming from WLMI (FM 103.9)?
NOTE: (memorize! )
FM signals are at a frequency of MHz
AM signals are at a frequency of kHz

29. Planck’s Hypothesis
Planck’s hypothesis
Max Planck didn’t believe that energy traveled in waves. He thought that it traveled in specific little packets called quanta. (think of a “quantity” meaning some specific amount). His theory is called the quantum theory.

30. Matter can gain or lose energy only in small, specific amounts called quanta.
A quantum is the minimum amount of energy that can be gained or lost by an atom.
A photon is defined as a quantum of radiant energy. It is a particle of electromagnetic radiation with no mass that carries a quantum of energy

31. Planck’s equation to calculate the energy of a photon: E = hn
E and n are directly proportional to each other, which means that as one goes up, the other goes up, too.
h = Planck’s constant = x J/Hz
or = x J s
example: What is the energy of the radiation coming from a photon of energy WLMI?

32. Other examples of calculations
What is the frequency of red light that measure 750. nanometers?

33. What is the wavelength of electromagnetic radiation from AM channel 1250?

34. What would be the energy from a photon of green light that measures 500. nanometers?

35. The Particle Nature of Light (cont.)
The photoelectric effect is when electrons are emitted from a metal’s surface when light of a certain frequency shines on it. Einstein won Nobel prize for defining this.
Section 5-1

36. The Particle Nature of Light (cont.)
Albert Einstein proposed in 1905 that light has a dual nature because the wave model of light cannot explain all of light’s characteristics
A beam of light has wavelike and particle-like properties. This is referred to as “wave-particle duality”.
Section 5-1

37. Atomic Emission Spectra
Light in a neon sign is produced when electricity is passed through a tube filled with neon gas and excites the neon atoms.
The excited atoms emit light to release energy and you see a color (spectrum) as atoms go back to ground state.
Section 5-1

38. The first three spectra are the emission spectra of excited gases of hydrogen (H), mercury (Hg), and neon (Ne).
The bottom spectrum is the absorption spectrum of hydrogen.

39. Atomic Emission Spectra (cont.)
Section 5-1

40. Atomic Emission Spectra (cont.)
The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element.
Each element’s atomic emission spectrum is unique.
Section 5-1

41. Review of the two equations
c = ln
c = ____________
l = ________ in __________
= ___________ in __________
Kind of proportion? _____________
What two things are proportional? ______________
E = hn
E = _________ in ___________
h = ___________________
n = __________ in __________
Kind of proportion? _________
What two things are proportional? ____________

43. Review of the two equations
c = ln
c = speed of light in m/s [3.00 x 108 m/s]
l = wavelength in m
= frequency in 1/s or Hz
Kind of proportion? inverse
What is proportional? l and n
note: (constants are NOT proportional!)
E = hn
E = energy in Joules (J)
h = planck’s constant [6.626 x J/Hz]
n = frequency in Hz
Kind of proportion? direct
What is proportional? E and n