1. Anyone who is not shocked by quantum mechanics has not understood it. —Neils Bohr (1885–1962)

2. December 3 Objectives: View emission spectrum of Hydrogen, identify the color bands Understand Bohr’s model of the atom

3. Observations Look at the light produced by the hydrogen lamp What color is it? Put on your diffraction glasses What colors can you see now?

4. This means hydrogen is producing specific bands of light with definite wavelengths/ frequencies. Hydrogen Emission Spectrum: Pink light emitted from hydrogen When separated by a prism, shows distinct bands of color

5. Niels Bohr Nobel Prize – 1922 “For his services in the investigation of the structure of atoms and the radiation emanating from them” Five facts from the next four slides…

6. Niels Bohr’s Atom (Slide 1 of 3) Electrons move around the nucleus in orbits, like a solar system. The orbits are sometimes called energy levels. Planetary Model Electrons cannot exist between orbits (energy is quantized)

7. (Slide 1b of 3) Electrons cannot exist between orbits – think of rungs on a ladder. You can’t be in between one rung and another.

8. Bohr’s Atom (Slide 2 of 3) Electrons closest to the nucleus are lowest in energy. Electrons farthest from the nucleus are highest in energy. Ground state- electrons are in the lowest energy level possible Excited state - If energy is put into the atom, the electrons will jump up in energy (move away from the nucleus)

9. Bohr’s Atom (Slide 3 of 3) Excited electrons naturally go back to ground state. In order to do this, energy must leave the atom. Because energy is quantized in an atom, the amount of energy that leaves is the difference in energy between orbits. If this energy is in the visible light range, we will see certain colors

10. Atomic Spectra Absorption: When energy is added and an electron moves from a lower energy level to a higher energy level Emission: When an electron falls from a higher energy level to a lower energy level and a photon is emitted. The energy of each absorbed or emitted photon corresponds to a particular frequency, E = hν

12. Hydrogen Atom Line Emission Spectrum Ground State: Lowest energy Excited State: Higher energy When an electron “falls” from higher to lower energy, it gives off extra energy (E) as a photon (E=hν)

13. This produces bands of light with definite wavelengths. Electron transitions involve jumps of definite amounts of energy. Hydrogen Emission Spectrum: Pink light emitted from hydrogen When separated by a prism, shows distinct bands of color

14. Electron at highest energy level produces what kind of EMR? - UV The electron at lowest energy level? - Red

15. IMPLICATIONS Classical Theory: (old) Any amount of energy could be absorbed or emitted Quantum Theory: (new) Hydrogen atoms can only have EXACT energy levels

16. One More Thing in the Notes Summary: Write a 1-2 sentence summary of the Bohr model of the atom and the hydrogen emission spectrum.

17. Flame Tests strontiumsodiumlithiumpotassiumcopper Many elements give off characteristic light which can be used to help identify them.

18. Next time - Thursday Flame Test Lab You will determine the emission spectra of a number of elements using colored flames Close-toed shoes Ladies: Something to tie your hair back