Bohr Model of the Atom

1. Ch. 5 - Electrons in Atoms Bohr Model of the Atom

2. 5.1 The Development of Atomic Models • The timeline shows the development of atomic models from 1803 to 1911.

3. 5.1 The Development of Atomic Models • The timeline shows the development of atomic models from 1913 to 1932.

4. Atomic Line Emission Spectra and Niels Bohr • Bohr’s greatest contribution to science was in building a simple model of the atom. • It was based on an understanding of theLINE EMISSION SPECTRAofexcited atoms. Niels Bohr (1885-1962)

5. Other Elements • Each element has a unique bright-line emission spectrum. • “Atomic Fingerprint” Helium • These bright - color lines are created by electrons changing energy levels

6. Line Spectra of Other Elements

7. Bohr Model • e-exist in orbits with specific amounts of energy called energy levels • Therefore… • e- can only gain or lose certain amounts of energy (QUANTUM), when they change energy levels • photons, which are a quantum of light are produced, when an electron changes energy levels

8. Quantized Energy comes in discrete packages Example: second hand on clock that “ticks” STAIRS Continuous Energy is flowing Example: second hand on clock that moves continuously ESCALATOR Quantized vs. Continuous

9. Bohr’s Model } • Further away from the nucleus means more energy. • There is no “in between” energy • Each rung on the ladder represents, energy level in the atom • Energy levels are not the same “size” Fifth Fourth Third Increasing energy Second First Nucleus

10. Changing the energy • Let’s look at a hydrogen atom

11. Where the electron starts • The energy level and electron starts from is called its ground state.

12. Excitation • When an electron is raised to a higher energy level, the atom absorbs energy and is said to be excited. • When the electron returns to a lower energy level, energy isreleased in the form of light.

13. Changing the energy • Heat or electricity or light can move the electron up energy levels

14. Changing the energy • As the electron falls back to ground state it gives the energy back as light.

15. Changing the energy • May fall down in steps • Each with a different energy

16. Line-Emission Spectrum excited state ENERGY IN PHOTON OUT ground state

17. Energy of photon released depends on the difference in energy levels Bohr’s experiments only dealt with hydrogen at the time Bohr Model 6 5 4 3 2 1

18. Spectrum of Excited Hydrogen Gas

19. Flame Tests Many elements give off characteristic light which can be used to help identify them. strontium lithium potassium copper sodium