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The ELECTRON: Wave – Particle Duality

“No familiar conceptions can be woven around the electron. Something unknown is doing we don’t know what.” -Sir Arthur Eddington The Nature of the Physical World (1934). The ELECTRON: Wave – Particle Duality. The Dilemma of the Atom.

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The ELECTRON: Wave – Particle Duality

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  1. “No familiar conceptions can be woven around the electron. Something unknown is doing we don’t know what.” -Sir Arthur Eddington The Nature of the Physical World (1934) The ELECTRON:Wave – Particle Duality

  2. The Dilemma of the Atom • Electrons outside the nucleus are attracted to the protons in the nucleus • Charged particles moving in curved paths lose energy • What keeps the atom from collapsing?

  3. Wave-Particle Duality JJ 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 a particle! The electron is an energy wave!

  4. The Wave-like Electron The electron propagates through space as an energy wave. To understand the atom, one must understand the behavior of electromagnetic waves. Louis deBroglie

  5. Electromagnetic radiation propagates through space as a wave moving at the speed of light. c = f c = speed of light, a constant (3.00 x 108 m/s) f = frequency, in units of hertz (hz, sec-1)  = wavelength, in meters

  6. The energy (E ) of electromagnetic radiation is directly proportional to the frequency () of the radiation. E = hf E= Energy, in units of Joules (kg·m2/s2) h= Planck’s constant (6.626 x 10-34 J·s) f= frequency, in units of hertz (hz, sec-1)

  7. Long Wavelength = Low Frequency = Low ENERGY Wavelength Table Short Wavelength = High Frequency = High ENERGY

  8. Answering the Dilemma of the Atom • Treat electrons as waves • As the electron moves toward the nucleus, the wavelength shortens • Shorter wavelength = higher energy • Higher energy = greater distance from the nucleus

  9. The Electromagnetic Spectrum

  10. Electron transitionsinvolve jumps of definite amounts ofenergy. This produces bands of light with definite wavelengths.

  11. Spectroscopic analysis of the hydrogen spectrum… …produces a “bright line” spectrum

  12. Flame Tests Many elements give off characteristic light which can be used to help identify them. strontium sodium lithium potassium copper

  13. Electron Orbitals Cartoon courtesy of lab-initio.com

  14. The Bohr Model of the Atom I pictured electrons orbiting the nucleus much like planets orbiting the sun. But I was wrong! They’re more like bees around a hive. Neils Bohr

  15. Quantum MechanicalModel of the Atom Mathematical laws can identify the regions outside of the nucleus where electrons are most likely to be found. These laws are beyond the scope of this class…

  16. 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

  17. Electron Energy Level (Shell) Generally symbolized by n, it denotes the probable distance of the electron from the nucleus. “n” is also known as the Principle Quantum number Number of electrons that can fit in a shell: 2n2

  18. An orbital is a region within an energy level where there is a probability of finding an electron. Electron Orbitals Orbital shapes are defined as the surface that contains 90% of the total electron probability.

  19. sOrbital shape The s orbital has a spherical shape centered around the origin of the three axes in space.

  20. d orbital shapes Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells” …and a “dumbell with a donut”!

  21. porbital shape There are three dumbbell-shaped porbitals in each energy level above n = 1, each assigned to its own axis (x, y and z) in space.

  22. d orbital shapes Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells” …and a “dumbell with a donut”!

  23. Shape of f orbitals

  24. Energy Levels, Orbitals, Electrons

  25. Orbital filling table

  26. Electron Spin Electron spin describes the behavior (direction of spin) of an electron within a magnetic field. Possibilities for electron spin:

  27. Electron Spin Electron spin describes the behavior (direction of spin) of an electron within a magnetic field. Possibilities for electron spin:

  28. Pauli Exclusion Principle Two electrons occupying the same orbital must have opposite spins Wolfgang Pauli

  29. Electron configuration of the elements of the first three series

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