Atomic Models

1. Atomic Models

2. Atomic Models The Adventures of J.J. Thomson, Plum Pudding and the Electron! MMMMM…..That plum pudding looks delicious!

3. I LOVE plum pudding! Atomic Models JJ Thomson: • English Physicist • Experimented with “cathode rays” • Was able to determine that the mass of the particles in the ray was much smaller than the mass of a hydrogen atom • The particle must be a smaller than an atom!

4. Atomic Models JJ Thomson’s Cathode Ray Tube (CRT) Anode – attached to the positive terminal of the voltage source Cathode – attached to the Negative end of the voltage source

5. Atomic Models A magnet placed near the tube deflected the beam, proving it was negatively charged. A small paddlewheel in the tube turned when hit by the beam, meaning the particles had mass.

6. Atomic Models Thompson called the negatively charged particles in the beam “corpuscles” This name was later changed to “electrons” by one of Thompson’s associates.

7. Atomic Models Thompson’s Conclusion: • An atom is a sphere of positive charge with electrons embedded in it “Plum-Pudding” Model of the Atom

8. Atomic Models In 1909, one of his students, Ernest Rutherford, disproved the “Plum Pudding” model by doing is famous “Gold Foil” experiment.

9. Atomic Models Rutherford’s experiment http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

10. Atomic Models • What conclusions were drawn from Rutherford’s Experiment?

11. Atomic Models Rutherford’s Model of the Atom: • Electrons orbit the nucleus just as planets • orbit the sun • Did not explain why the negatively charged electrons did not crash into the positively charged nucleus.

12. Atomic Models Two years later, Danish physicist, Niels Bohr, proposed the Bohr Model of the atom

13. Atomic Models Bohr’s Model • Electrons are located certain distances from the nucleus • Each distance is a certain quantity of energy that the electron can have

14. Atomic Models • Electrons closest to the nucleus have the lowest energy, while the ones further away are in higher energy levels

15. Atomic Models • The difference between two energy levels is called a quantum of energy. • Electrons can be only in an energy level, NOT between levels.

16. Atomic Models Electrons and Light (pg. 92) Basic Information: • Light travels in waves • Each wave has a certain wavelength (distance between two consecutive peaks of a wave)

17. Atomic Models Each wavelength has a certain frequency (the # of waves that pass through a specific point in one second)

18. Atomic Model Light and the Visible Electromagnetic Spectrum • We can only see a small amount of the electromagnetic spectrum • Bohr found that if you pass a high voltage through a gas and look at it through a prism, it will have a distinctive pattern of colored lines called “line-emission spectrum”

19. Atomic Models Bohr calculated that the line-emission spectrum corresponded to energy levels in the atom (which give off a different wavelength of visible light) • The colors are caused when an electron falls from its excited state to its ground state and gives off energy in the form of light! (pg. 94)

20. Atomic Models Great video on line-emission spectrum http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf

21. Spectrum of a Fluorescent Light

22. Spectrum