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LIGHT and the ATOMIC SPECTRA of ELEMENTS

LIGHT and the ATOMIC SPECTRA of ELEMENTS. To Recap… . For most purposes light is said to exhibit wave-like properties . Light consists of electromagnetic waves. Electromagnetic Radiation includes…. Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.

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LIGHT and the ATOMIC SPECTRA of ELEMENTS

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  1. LIGHT and the ATOMIC SPECTRA of ELEMENTS

  2. To Recap… • For most purposes light is said to exhibit wave-like properties. • Light consists of electromagnetic waves

  3. Electromagnetic Radiation includes… • Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.

  4. The product of frequency and wavelength is equal to the speed of light. C = λν C = speed of light λ = wavelength ν = frequency

  5. The frequency and wavelength of light waves are inversely related. As the wavelength decreases, the frequency increases ν = c λ

  6. Every element emits light when it is excited by the passage of an electric discharge through its gas or vapor. • The atoms first absorb energy, then lose energy as they emit light. • Follow this link to observe. • http://www.colorado.edu/physics/2000/quantumzone/lines2.html

  7. Passing the light through a prism gives the atomic emission spectrum of the element. • White light gives off a continuous spectra.

  8. The spectra of most elements shows very few lines and are called line spectra or discontinuous spectra. • This is the spectra for mercury.

  9. This is the spectra for neon

  10. The emission spectra of each element is unique and can be used to identify that element. • Bohr’s idea of energy levels resulted in an explanation of the hydrogen spectrum.

  11. Hydrogen has one electron in its lowest energy level-called the ground state. The quantum number (n) is 1. • Exciting the electron raises it to higher energy levels such that n = 2, 3, 4 and so on.

  12. It takes a specific amount of energy (a quantum) to raise an electron to a higher energy level. • The same amount of energy is emitted as a photon when the electron drops back to the ground state. • Revisit this tutorial • http://www.colorado.edu/physics/2000/quantumzone/lines2.html

  13. Only electrons in transition from higher to lower energy levels lose energy and emit light. • There are 3 lines in the emission spectrum for hydrogen.

  14. The 3 groups of lines correspond to the transition of electrons from higher energy levels to lower energy levels. • The Lyman series (ultraviolet range) corresponds to transitions from high energy levels to n = 1 (ground state).

  15. The Balmer series (visible range) correspond to transitions from higher energy levels to n = 2 (2nd energy level).

  16. The Paschen series (infrared range) corresponds to the transition from higher energy levels to n = 3 (or 3rd energy level).

  17. Consider these questions 1- Suppose an electron is excited enough to jump to energy level 2. When it returns to the ground state, what type of radiation will it emit?

  18. 2- If you observed a hydrogen gas discharge tube through a diffraction grating, would you be able to see the line corresponding to this emission? (from previous question)

  19. 3- Which series of lines would you be able to detect? 4- What do you notice about the spacing of the energy levels from n= 1 to n= 7?

  20. Quantum Mechanics • Light as waves, light as particles, energy absorbed and emitted in packages? All that and more • De Broglie derived an equation that described the wavelength of a moving particle. λ = h m v

  21. His equation predicts that all particles of matter exhibit wavelike properties. • Quantum mechanics changes the way observations are made. You can’t observe something without changing it in the process.

  22. EX- Suppose you want to find out if there is a car in a long tunnel. In quantum mechanics the only experiment you could do would be to send another car into the tunnel and wait for the crash. Although it is possible to detect the presence of a car, it is obvious the car will be changed by the crash.

  23. Heisenberg Uncertainty Principle • This states that it is impossible to know exactly both the velocity and the position of a particle at the same time. • If a photon is emitted which tells us the position, the velocity will change due to the emission of the photon.

  24. FOR YOU 1- Explain the origin of the atomic emission spectrum of an element. 2- Compare the ground state and the excited state of an electron.

  25. 3- Arrange the following in order of decreasing wavelength: Infrared radiation from heat lamp Dental x-rays A signal from a shortwave radio station

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