1. Modern Atomic Theory Ms. Hoang ACP Chemistry

2. Summary  Visible light is a small section of the EM spectrum  Light exhibits wave-like and particle-like properties  To characterize wave, scientists use wavelength, frequency, speed (and amplitude)  Short wavelength = (high/low) frequency = (high/low) energy  Long wavelength = (high/low) frequency = (high/low) energy  Wavelength determines color of light  White light is light of all wavelengths  Objects around us absorb visible light of different wavelengths and emit light of different wavelengths. That is why objects appear to have colors.

3. Concept Check-in  What color is a banana under white light?  Yellow  What color is a banana under green light?  Black

4. Objectives  Use light and wave formulae to calculate wavelength and frequency of light  Contrast continuous spectra with line spectra  Explain why the emission spectra of elements are line spectra rather than continuous spectra

5. Light and Wave formulae h = 6.626 x 10 -34 J.s | 1nm = 1.00 x 10 -9 m

6. Example  A photon has an energy of 4.00 x 10 -19 J.  Find the frequency of the radiation  Find the wavelength of the radiation  Find the color of the photon if possible

7. Your turn  A photon has an energy of 3.00 x 10 -19 J.  Find the frequency of the radiation  Find the wavelength of the radiation  Find the color of the photon if possible

8. Your turn  A bright line spectrum contains a line with a wavelength of 518 nm.  The color of the line is:  A. Violet  B. Green  C. Yellow  E. Red  The energy is:  A. 5.12 x 10 -23 J  B. 3.84 x 10 19 J  C. 5.12 x 10 23 J  D. 3.84 x 10 -19 J

9. Flame Test revisit

11. Energy is quantized

12. Flame Test revisit

13. Types of spectra  Continuous vs. Line  How do we know? Spectroscope

14. Types of spectra  _______ light = contains light of all wavelengths  __________  Light from an excited element (electrical current) = contains light of _______ wavelengths  _____________  Question: Why do atoms emit line spectra?

15. Hydrogen atom Emission Spectrum for Hydrogen

16. Bohr Model of the Atom  Electrons go in orbits around the nucleus like the solar system  Each orbit is a discrete  Only works for Hydrogen atom

17. n = 3 n = 2 n = 1

18. Emission and Absorption Spectra

19. Cosmos – Hiding in the Light

20. Wave Mechanical Model of the Atom  Orbitals = electron cloud = probability map of finding electrons = easier to find electrons in the shaded regions  The size of an atom is described as 90% probability of finding an electron at a given point in space