1. Hydrogen Spectral Lines

2. Bohr Model of the Atom Electrons in Atoms nucleus (+) electron (-) Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

3. Atomic Spectrum How color tells us about atoms

4. Prism zWhite light is made up of all the colors of the visible spectrum. zPassing it through a prism separates it. Author: Thomas V. Green Jr.

5. If the light is not white zBy heating a gas or with electricity we can get it to give off colors. zPassing this light through a prism does something different. Author: Thomas V. Green Jr.

6. Atomic Spectrum zEach element gives off its own characteristic colors. zCan be used to identify the atom. zHow we know what stars are made of. Author: Thomas V. Green Jr.

7. These are called line spectra unique to each element. These are emission spectra The light is emitted given off. Author: Thomas V. Green Jr.

8. Line-Emission Spectrum ground state excited state ENERGY IN PHOTON OUT Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem 656 nm486 nm 410 nm 434 nm Wavelength (nm) Prism Slits

9. Bohr Model electrons exist only in orbits with specific amounts of energy called energy levels Therefore… electrons can only gain or lose certain amounts of energy only certain photons are produced Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

10. Bohr Model 1 2 3 4 5 6 zEnergy of photon depends on the difference in energy levels zBohr’s calculated energies matched the IR, visible, and UV lines for the H atom Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem nucleus

11. Other Elements zEach element has a unique bright-line emission spectrum. i.e. “Atomic Fingerprint” Helium zBohr’s calculations only worked for hydrogen!  Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

12. Bohr’s Experiment Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 76 Animation by Raymond Chang – All rights reserved.

13. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. (a) Electronic absorption transition (b) H 2 emission spectrum (top), H 2 absorption spectrum (bottom)

14. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. (a) Electronic absorption transition (b) H 2 emission spectrum (top), H 2 absorption spectrum (bottom) Lower-energy orbit Higher-energy orbit Photon e-e- e-e-

15. continuous spectrum absorption spectrum emission spectrum hot source gas absorption spectrum emission spectrum

16. Hydrogen Spectral Lines Lyman series (ultraviolet) Balmer series (visible) Paschen series (infrared) Frequency (hertz) 10 16 10 15 10 14 7 6 5 4 3 2 1 n =

17. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. (ultraviolet) (visible) (infrared) HYDROGEN SPECTRAL LINES

18. Hydrogen Spectral Lines A B C D E F Lyman series (UV) A B C D E Balmer (Visible) A B C D Paschen (IR) E1E1 E2E2 E3E3 E4E4 E5E5 E6E6 Energy Bohr’s model of the atom accounted mathematically for the energy of each of the transitions shown. IR region UV region 656 nm 486 nm 434 nm 410 nm Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 97 ionization

19. Electronic Transitions in the Excited Hydrogen Atom