1. Light & Atomic Spectra & Nuclear Chemistry Planck’s Constant

2. Types of Light Visible light is the light that humans can see. Visible light is the light that humans can see.

3. Did you know? Dogs can see only shades of gray Dogs can see only shades of gray and some insects can see light from the ultraviolet part of the spectrum and some insects can see light from the ultraviolet part of the spectrum

4. Seeing the Light Visible light is the light that humans can see. Visible light is the light that humans can see. More specifically, you see the light that is not absorbed by objects. More specifically, you see the light that is not absorbed by objects. Green plants are green because they absorb all of the colors of the visible spectrum except the green color (you could also say the green wavelengths). Green plants are green because they absorb all of the colors of the visible spectrum except the green color (you could also say the green wavelengths).

5. Red A red wall is red to your eyes because it is not absorbing light from the red wavelengths. A red wall is red to your eyes because it is not absorbing light from the red wavelengths.

7. electromagnetic radiation Visible light is only one small portion of a family of waves called electromagnetic (EM) radiation. Visible light is only one small portion of a family of waves called electromagnetic (EM) radiation. EM waves includes radio waves, uv, infared, microwave, x-rays, gamma rays EM waves includes radio waves, uv, infared, microwave, x-rays, gamma rays Visible light is near the middle of the spectrum. Visible light is near the middle of the spectrum.

9. ROY-G-BIV ROY-G-BIV ROY-G-BIV represents all of the colors in the visible spectrum of light. R (red) - O (orange) - Y (yellow) - G (green) - B (blue) - I (indigo) - V (violet). represents all of the colors in the visible spectrum of light. R (red) - O (orange) - Y (yellow) - G (green) - B (blue) - I (indigo) - V (violet). Red has the longest wavelength and violet has the shortest. Red has the longest wavelength and violet has the shortest. You could also say that red is the least energetic and violet is the most energetic of the visible spectrum. You could also say that red is the least energetic and violet is the most energetic of the visible spectrum.

10. Prisms When refraction is at work in a prism it breaks the beam of visible light into its basic colors. When refraction is at work in a prism it breaks the beam of visible light into its basic colors. A prism is made up of two planar surfaces at an angle. A prism is made up of two planar surfaces at an angle. It uses the slower speed of light in glass to its advantage by refracting the light twice. It uses the slower speed of light in glass to its advantage by refracting the light twice. When the light ray leaves the prism, it speeds up again (entering the air) and refracts a second time. When the light ray leaves the prism, it speeds up again (entering the air) and refracts a second time. That second dispersal creates the colorful spectrum of colors. That second dispersal creates the colorful spectrum of colors.

11. Light waves are classified by frequency of wavelength Low frequency= long wavelength Low frequency= long wavelength High frequency= short wavelength High frequency= short wavelength

12. Parts of a wave Amplitude Amplitude height of the wave from normal to highest point. height of the wave from normal to highest point. Wavelength Wavelength the distance from origin to origin, crest to crest the distance from origin to origin, crest to crest Frequency Frequency 1 wave per period 1 wave per period measured in Hz (1Hz = 1wave per second). measured in Hz (1Hz = 1wave per second).

13. In 1900, Max Planck was working on the problem of how the radiation an object emits is related to its temperature. was working on the problem of how the radiation an object emits is related to its temperature. Planck's constant, the constant of proportionality relating the energy of a photon to its frequency; or h, and it has the value Planck's constant, the constant of proportionality relating the energy of a photon to its frequency; or h, and it has the value

14. The formula The energy E contained in a photon, the smallest possible 'packet' of energy, is directly proportional to the frequency f : The energy E contained in a photon, the smallest possible 'packet' of energy, is directly proportional to the frequency f : E photon = hf E photon = hf E = (6.626176 x 10 -34 J*s) * f (frequency) E = (6.626176 x 10 -34 J*s) * f (frequency) and conversely: and conversely: F (frequency) = E photon / (6.626176 x 10 -34 J*s) F (frequency) = E photon / (6.626176 x 10 -34 J*s) Frequency SI units are Hz or 1/s or s -1 Frequency SI units are Hz or 1/s or s -1

15. Sample Problem Example Problem: Calculate the energy in J of a quantum of radiant energy (the energy of a photon) with a frequency of 5.00 x 10 15 Hz. Example Problem: Calculate the energy in J of a quantum of radiant energy (the energy of a photon) with a frequency of 5.00 x 10 15 Hz. 1 st list the knowns: 1 st list the knowns: Frequency (f) = 5.00 x 10 15 Hz Frequency (f) = 5.00 x 10 15 Hz h= 6.626 x 10 -34 J*s (Planck’s constant) h= 6.626 x 10 -34 J*s (Planck’s constant) Unknown: E Unknown: E

16. Solve for the unknown: Solve for the unknown: E= h x f E= h x f E= (6.626 x 10 -34 J*s) x (5.00 x 10 15 1/s) E= (6.626 x 10 -34 J*s) x (5.00 x 10 15 1/s) E=3.31 X 10 -18 J E=3.31 X 10 -18 J

17. What is the energy of a photon of microwave radiation with a frequency of 3.20 x 10 -11 Hz? What is the energy of a photon of microwave radiation with a frequency of 3.20 x 10 -11 Hz?

18. What is the energy of a photon of green light with a frequency of 5.80 x 10 14 Hz?

19. Einstein Based on Planck's work, Einstein proposed that light also delivers its energy in chunks; light would then consist of little particles, or quanta, called photons, each with an energy of Planck's constant times its frequency. Based on Planck's work, Einstein proposed that light also delivers its energy in chunks; light would then consist of little particles, or quanta, called photons, each with an energy of Planck's constant times its frequency.

20. c=λf c=speed of light = 3.0 x 10 8 m/s λ= wavelength (make sure it is in meters (m) so the units will match) f=frequency in Hz

21. Sample Problem Calculate the wavelength of the yellow light emitted by a sodium lamp if the frequency of the radiation is 5.10 x 10 14 Hz Calculate the wavelength of the yellow light emitted by a sodium lamp if the frequency of the radiation is 5.10 x 10 14 Hz List the knowns: List the knowns: Frequency (f) = 5.10 x 10 14 Hz Frequency (f) = 5.10 x 10 14 Hz c=speed of light = 3.0 x 10 8 m/s c=speed of light = 3.0 x 10 8 m/s Unknown: Unknown: λ in m

23. What is the wavelength of radiation with a frequency of 1.50 x 10 13 Hz What is the wavelength of radiation with a frequency of 1.50 x 10 13 Hz

24. What frequency is radiation with a wavelength of 5.00 x 10 -6 cm? What frequency is radiation with a wavelength of 5.00 x 10 -6 cm?

25. It's all Energy The quantum theory says light consists of very small bundles of energy/particles called photons. Wavelength determines: energy & type of EM radiation Wavelength determines: energy & type of EM radiation # of photons: states how much radiation is present # of photons: states how much radiation is present

26. Photons determine how bright the light is…. Lots of photons give a brighter, more intense type of light. Lots of photons give a brighter, more intense type of light. Fewer photons give a very dim and less intense light. Fewer photons give a very dim and less intense light.

27. Think of a dimmer switch When you use the dimmer switch on the wall, you are decreasing the number of photons sent from the light bulb. The type of light is the same while the amount has changed.

28. Flame Test Lab Flame tests are used to identify the presence of a relatively small number of metal ions in a compound. Flame tests are used to identify the presence of a relatively small number of metal ions in a compound. Flame colors are produced from the movement of the electrons in the metal ions present in the compounds. Flame colors are produced from the movement of the electrons in the metal ions present in the compounds.

29. So in the flame, electrons get excited and pushed to higher energy levels electrons get excited and pushed to higher energy levels When they fall back down, they give off photons of light of different colors, based upon how far they fall. When they fall back down, they give off photons of light of different colors, based upon how far they fall.

30. For example, a sodium (na) ion in an unexcited state has the structure 1s 2 2s 2 2p 6. When heated: electrons gain energy and jump into any of the empty orbitals at higher levels – When heated: electrons gain energy and jump into any of the empty orbitals at higher levels – for example, into the 7s or 6p or 4d, depending on how much energy is absorbed from the flame. for example, into the 7s or 6p or 4d, depending on how much energy is absorbed from the flame. Because the electrons are now at a higher and more energetically unstable level, they tend to fall back down to where they were before Because the electrons are now at a higher and more energetically unstable level, they tend to fall back down to where they were before

31. It might fall straight back or jump through many levels… It might fall straight back or jump through many levels… Each of these jumps involves a specific amount of energy being released as light energy, and each corresponds to a particular color. Each of these jumps involves a specific amount of energy being released as light energy, and each corresponds to a particular color.

32. Whatever color is produced, tells you what element you have. Whatever color is produced, tells you what element you have. This is a great way to determine an unknown substance… This is a great way to determine an unknown substance…