Understanding the Quantum Mechanical Model and Atomic Spectra

1. chemistry

2. 5.3 Physics and the Quantum Mechanical Model • Neon advertising signs are formed from glass tubes bent in various shapes. An electric current passing through the gas in each glass tube makes the gas glow with its own characteristic color. You will learn why each gas glows with a specific color of light.

3. 5.3 Light • Light • How are the wavelength and frequency of light related?

4. 5.3 Light • The amplitude of a wave is the wave’s height from zero to the crest. • The wavelength, represented by  (the Greek letter lambda), is the distance between the crests.

5. 5.3 Light • The frequency, represented by  (the Greek letter nu), is the number of wave cycles to pass a given point per unit of time. • The SI unit of cycles per second is called a hertz (Hz).

6. 5.3 Light • The wavelength and frequency of light are inversely proportional to each other. • As wavelength (λ) increases, frequency decreases. • As wavelength (λ) decreases, frequency increases. increases.

7. 5.3 Light • The product of the frequency and wavelength always equals a constant (c), the speed of light.

8. 5.3 Light • According to the wave model, light consists of electromagnetic waves. • Electromagnetic radiation includes radio waves, radar, microwaves, infrared waves, visible light (ROY G BIV), ultraviolet waves, X-rays, and gamma rays. (add sketch slide 10) • All electromagnetic waves travel in a vacuum at a speed of 2.998  108 m/s.

9. 5.3 Light • Sunlight consists of light with a continuous range of wavelengths and frequencies. • When sunlight passes through a prism, the different frequencies separate into a spectrum of colors. • In the visible spectrum, red light has the longest wavelength and the lowest frequency.

10. 5.3 Light • The electromagnetic spectrum consists of radiation over a broad band of wavelengths. P 139.

11. Light • Simulation 3 • Explore the properties of electromagnetic radiation.

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16. for Sample Problem 5.1 Problem-Solving 5.15 Solve Problem 15 with the help of an interactive guided tutorial.

17. 5.3 Atomic Spectra • Atomic Spectra • What causes atomic emission spectra?

18. 5.3 Atomic Spectra • When atoms absorb energy, electrons move into higher energy levels. These electrons then lose energy by emitting light when they return to lower energy levels.

19. 5.3 Atomic Spectra • A prism separates light into the colors it contains. When white light passes through a prism, it produces a rainbow of colors.

20. 5.3 Atomic Spectra • When light from a helium lamp passes through a prism, discrete lines are produced.

21. 5.3 Atomic Spectra • The frequencies of light emitted by an element separate into discrete lines to give the atomic emission spectrum of the element. Mercury Nitrogen

22. 5.3 An Explanation of Atomic Spectra • An Explanation of Atomic Spectra • How are the frequencies of light an atom emits related to changes of electron energies?

23. 5.3 An Explanation of Atomic Spectra • In the Bohr model, the lone electron in the hydrogen atom can have only certain specific energies. • When the electron has its lowest possible energy, the atom is in its ground state. • Excitation of the electron by absorbing energy raises the atom from the ground state to an excited state. • A quantum of energy in the form of light is emitted when the electron drops back to a lower energy level. See p. 143, figure 5.14

24. 5.3 An Explanation of Atomic Spectra • The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.

25. 5.3 An Explanation of Atomic Spectra • The three groups of lines in the hydrogen spectrum correspond to the transition of electrons from higher energy levels to lower energy levels. See p. 143.

26. An Explanation of Atomic Spectra • Animation 6 • Learn about atomic emission spectra and how neon lights work.

27. 5.3 Quantum Mechanics • Quantum Mechanics • How does quantum mechanics differ from classical mechanics?

28. 5.3 Quantum Mechanics • In 1905, Albert Einstein successfully explained experimental data by proposing that light could be described as quanta of energy. • The quanta behave as if they were particles. • Light quanta are called photons. • In 1924, De Broglie developed an equation that predicts that all moving objects have wavelike behavior.

29. What is light? • Light is a particle - it comes in chunks. • Light is a wave - we can measure its wavelength and it behaves as a wave • If we combine E=mc2 , c=f, E = 1/2 mv2 and E = hf, then we can get:  = h/mv (from Louis de Broglie) • called de Broglie’s equation • Calculates the wavelength of a particle.

30. Wave-Particle Duality J.J. Thomson won the Nobel prize for describing the electron as a particle. His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The electron is an energy wave! The electron is a particle!

31. Confused? You’ve Got Company! “No familiar conceptions can be woven around the electron; something unknown is doing we don’t know what.” Physicist Sir Arthur Eddington The Nature of the Physical World 1934

32. The physics of the very small • Quantum mechanics explains how very small particles behave • Quantum mechanics is an explanation for subatomic particles and atoms as waves • Classical mechanics describes the motions of bodies much larger than atoms

33. 5.3 Quantum Mechanics • Today, the wavelike properties of beams of electrons are useful in magnifying objects. The electrons in an electron microscope have much smaller wavelengths than visible light. This allows a much clearer enlarged image of a very small object, such as this mite.

34. Quantum Mechanics • Simulation 4 • Simulate the photoelectric effect. Observe the results as a function of radiation frequency and intensity.

35. 5.3 Quantum Mechanics • Classical mechanics adequately describes the motions of bodies much larger than atoms, while quantum mechanics describes the motions of subatomic particles and atoms as waves.

36. Heisenberg Uncertainty Principle “One cannot simultaneously determine both the position and momentum of an electron.” You can find out where the electron is, but not where it is going. OR… You can find out where the electron is going, but not where it is! Werner Heisenberg

37. 5.3 Quantum Mechanics • The Heisenberg Uncertainty Principle

38. 5.3 Quantum Mechanics • The Heisenberg uncertainty principle states that it is impossible to know exactly both the velocity and the position of a particle at the same time. • This limitation is critical in dealing with small particles such as electrons. • This limitation does not matter for ordinary-sized object such as cars or airplanes.

40. It is more obvious with the very small objects • To measure where a electron is, we use light. • But the light energy moves the electron • And hitting the electron changes the frequency of the light.

41. 5.3 Section Quiz. • 5.3.

42. 5.3 Section Quiz. • 1. Calculate the frequency of a radar wave with a wavelength of 125 mm. • 2.40 109 Hz • 2.40 1024 Hz • 2.40 106 Hz • 2.40 102 Hz

43. 5.3 Section Quiz. • 2. The lines in the emission spectrum for an element are caused by • the movement of electrons from lower to higher energy levels. • the movement of electrons from higher to lower energy levels. • the electron configuration in the ground state. • the electron configuration of an atom.

44. 5.3 Section Quiz. • 3. Spectral lines in a series become closer together as n increases because the • energy levels have similar values. • energy levels become farther apart. • atom is approaching ground state. • electrons are being emitted at a slower rate.

45. www.chembored.com • Chem 12 • Quantum mechanics: the sequel • Overlapping shells slide: slide 9 (this is the 2nd day of the quantum mechanics lesson).

46. Concept Map 5 Concept Map 5 Solve the concept map with the help of an interactive guided tutorial.

47. END OF SHOW