The Quantum Model of the Atom Part 1

1. The Quantum Model of the Atom Part 1 Electrons as Waves

2. The Word for the day is… • Quantized- Only certain specific values are allowed. • The electron’s energy is quantized. This means that it can only have certain specific amounts of energy at a given time

3. Quantized • What if the accelerator on your car was quantized? • Is it? What do you think?

4. My fingerprint looks like this • An Elements fingerprint looks like this

5. Atomic Emission Spectrum

6. We need someone who could make a connection between the atomic emission spectrum of an element and the model of an atom • And his name was • Bohr • Neils Bohr

7. How did Bohr’s model explain the bright line spectrum produced by hydrogen? • When the atom absorbs energy the electron “jumps” to a higher energy level (orbit). • When the electron “falls” to a lower orbit the energy is released as a photon of light. • The color of light produced corresponds to the size of the energy change. • Remember this equation: • E = hf

8. What type of spectrum is produced when hydrogen emits light and why? • A bright line or atomic emission spectrum is produced … NOT a continuous spectrum • The electron’s energy levels are quantized. • Electrons can only absorb or release certain specific amounts of energy. Thus… …only certain specific colors, frequencies or photons (energies) of light can be produced!

9. Bohr Model of the Atom

11. How does the photon that is emitted (the released energy) correspond to the colored lines we see in the atomic emission spectrum? • Lets look again at Hydrogen

12. Remember

15. Why are only certain specific colors produced? • Because the electron can only have certain specific amounts of potential energy. In other words, it is quantized! • Thus, the electron can only absorb or release certain specific amounts of energy…corresponding to the specific colors in it’s atomic emission spectrum.

16. HOMEWORK • Read pages 135-137 • Answer questions #1,2 on page 140 • Look at slide #14, what is wrong with this image?

18. What did Bohr’s Model Give Us • Three important idea’s: • 1 – Electron’s exist in stable orbits about the nucleus • 2 – Only certain orbits are allowed • 3 - An electron passing from a lower orbit to a higher orbit must absorb light with exactly the difference in energy between the two orbits. Similarly, for an electron to move from a higher orbit to a lower one, it must emit light corresponding to exactly the difference in energy.

19. What were the shortcomings of Bohr’s model of the atom? • Scientists did not understand why the electron could only exist in certain specific orbits or energy levels? (quantized) • It worked perfectly for hydrogen (1 electron) but not for the other elements.

20. Matter Waves-The wave-like behavior of particles

21. Louis de Broglie • de Broglie Hypothesis states that any moving particle or object has an associated wave. • For this he won the Nobel Prize in Physics in 1929 • Tiny electrons behave similar to waves • When confined to a space, waves can only have certain frequencies (energies). Thus, they are quantized like electrons in Bohr’s model. • Light has a dual (particle/wave) nature. The electron has a dual (particle/wave) nature as well.

22. Lets take a look at the Double Slit Experiment http://www.youtube.com/watch?v=DfPeprQ7oGc

23. Every object has wave properties • De Broglie wavelength equation • An electron that has a mass of 9.11 x 10-28 g is traveling at 90 mi/hr • It has a wavelength of 2 x 10-5 m measured in the IR section • A baseball that has a mass of 0.15 kg that is pitched at 90 mi/hr • It has a wavelength of 1.1 x 10-34 m, not measurable by any instrument

24. Homework • Read pg 137 – 140 • Answer question #3 on page 140 • Answer question #18 on pg 157

25. Heisenberg’s Uncertainty Principle • It is impossible to determine simultaneously the position and velocity of an electron or any other particle. • This is due to the fact that by observing an electron, the measurement itself will cause the electron to change position. Light will interact with an electron and cause it to move. • The way around this problem is to describe electron location in terms of probability of finding the electron in certain regions in the atom.

26. Werner Heisenberg is speeding down a highway, when he's pulled over by the police. The cop walks up to him and says, "Excuse me, sir, do you know how fast you were driving?" • Heisenberg looks up to the officer and says, "Nope, but I know exactly where I was!"

27. SchrÖdinger’s Wave Equation Memorize this equation Just Kidding

28. SchrÖdinger’s Wave Equation • Equation describes the wave properties of electrons and other small particles. • Proved quantization • Only waves of specific energies and therefore frequencies provide solutions to the equation • Describes the arrangement of electrons in atoms.

29. Together, the ideas that electrons are quantized, the de Broglie wave properties, the Heisenberg uncertainty principle and the addition of the Schrödinger wave equation laid the foundation for the development of the quantum-mechanical model of an atom.

30. The modern electron cloud model (a.k.a. quantum-mechanical model) shows electrons orbiting around the nucleus in specific regions (or “clouds”) based on the probability of finding them within that region.

31. Yet again another modification to the atomic model Lets take a look back

32. Orbitals • ORBITAL ≠ ORBIT • A three dimensional region around the nucleus that indicates the most probable location of an electron with a given energy. • Higher probability – higher electron density • Lower probability – lower electron density • There are several different types of orbitals each having a different fundamental shape.

39. The 5 d orbitals http://www.winter.group.shef.ac.uk/orbitron/AOs/3d/index.html http://www.falstad.com/qmatom/