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Arrangement of Electrons in Atoms Part One

Arrangement of Electrons in Atoms Part One. Learning Objectives Read Pages 97-106 Asgn #16: 103/1-6. Section 1 Light and Electrons. Explain the mathematical relationship amount the speed, wavelength, and frequency of electromagnetic radiation. Discuss the dual wave-particle nature of light.

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Arrangement of Electrons in Atoms Part One

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  1. Arrangement of Electronsin AtomsPart One Learning Objectives Read Pages 97-106 Asgn #16: 103/1-6

  2. Section 1 Light and Electrons • Explain the mathematical relationship amount the speed, wavelength, and frequency of electromagnetic radiation. • Discuss the dual wave-particle nature of light. • Discuss the significance of the photoelecvtric effect and the line-emission spectrum of H to the development of the atomic model. • Describe the Bohr model of the H atom.

  3. Section 2 Quantum Model • Discuss De Broglie’s role in the development of the quantum model of the atom. • Compare and contrast the Bohr model and the quantum model of the atom. • Explain how the Heisenberg uncertainty principle and the Schrodinger wave equation led to the idea of atomic orbitals.

  4. Electromagnetic Radiation (EMR) or light is a form of energy that moves as a wave through space. • Electromagnetic Spectrum is made up of many kinds of EMR: visible, X rays, ultraviolet, infrared, microwaves, and radiowaves.

  5. Electromagnetic (E-M) Waves (LIGHT!) Do not require a medium through which to travel Light travels at 3.0 x 108 m/s in a vacuum or air Its wavelength and frequency varies according to the type of E-M wave

  6. Higher frequency  Greater energy  More penetration • What type has • Greatest frequency? • Less frequency than infrared light?

  7. c = ln • c , the speed of light which is 3x108 m/s in a vacuum or air. Units: m/s • l, wavelength or distance between corresponding points on adjacent waves • Units: m or nm • n, frequency or number of waves passing a point in a given amount of time. Units: Hertz, Hz or 1/s or s-1

  8. Light Problems: What is the frequency of light whose wavelength is 600 nm? • nm means 10-9 m • c = ln --> n = c/l = • 3x108 m = 5 x 1014 s-1 • 600x10-9 m s

  9. Photoelectric Effect • This is the emission of electrons from a metal when electromagnetic radiation shines on the metal. P. E. shows that energy is emitted in small, specific packets called quanta. A quantum of energy is the minimum quantity of energy that can be lost or gained by an atom. The photoelectric effect showed that light behaves as particles, too!

  10. E = h n * • E, energy of a quantum of radiation in joules, J • h, Planck’s constant is 6.626 x 10-34 Js • n, frequency in s-1 • Problem: What is the frequency of a photon whose energy is 3.4 x 10-19 J? • n = E/h = 3.4 x 10-19 J / 6.626 x 10 -34 Js • n = 5.1 x 1014 s-1 *Wavelength-frequencyrelationship was proposed by Planck in 1900.

  11. Einstein explained the photoelectric effect was due to metal absorbing energy in discrete amounts of photons. • Ground state – lowest energy state of an atom • Excited state – state where an atom has a higher potential energy than ground state.

  12. webexhibits.org

  13. Tutorvista.com

  14. Bohr Model • 1913 – Niels Bohr proposed a hydrogen atom model where electrons circle the nucleus only in allowed paths or orbits with a definite amount of energy. • If an electron absorbs energy, it can go to a higher level. • If in a higher energy level, an electron can emit a certain amount of energy to move to a lower level.

  15. chemweb.ucc.ie

  16. Quantum Model of the Atom • Questions were unanswered regarding how electrons could be particles yet they gave off waves of light. • De Broglie suggested that electrons could be considered waves confined to space around a nucleus only at specific frequencies. • Diffraction experiments proved that electron beams can interfere with each other and produce areas of low energy and high energy areas as a result of interference.

  17. Heisenberg Uncertainty Principle (1927) – it is impossible to determine simultaneously both the position and velocity of an electron or any other particle. • Schrodinger Wave Equation (1926) - developed an equation that treated electrons in atoms as waves. • Heisenberg and Schrodinger laid the foundation for mathematical descriptions of wave properties of very small particles such as electrons – the probable location of electrons around the nucleus. • AKA: Quantum Theory and Quantum Numbers.

  18. End of Section 1 and part of Section 2 of Chapter 4 • Arrangement of Electrons in Atoms

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