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Chapter 5

Chapter 5. The Electron. Light. A form of electromagnetic radiation Characteristics of both wave & particle. Waves. Wavelength (λ)- shortest distance between equivalent points on a continuous wave Measured in m, cm, or nm Crest - top of wavelength Trough - bottom of wavelength

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Chapter 5

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  1. Chapter 5 The Electron

  2. Light • A form of electromagnetic radiation • Characteristics of both wave & particle

  3. Waves

  4. Wavelength(λ)- shortest distance between equivalent points on a continuous wave • Measured in m, cm, or nm • Crest- top of wavelength • Trough- bottom of wavelength • Frequency(v)- number of waves that pass a certain point per second • Measured in waves/second • Hertz(Hz)- SI unit for frequency • Equal to 1 wave/second or 1/second • Amplitude- the wave’s height from it’s origin to it’s crest or trough • λ & v do not affect amplitude

  5. Waves (cont.) • All electromagnetic waves travel at a speed of 3.00 X 108 m/s in a vacuum • The symbol for the speed of light is c. • c=λv

  6. Quantum- minimum amount of energy that can be gained or lost by an atom • Energy of quantum= hv where h is Planck’s constant (6.626 x 10-34 Js, and v is the frequency

  7. Photon- a massless particle that carries a quantum of energy. • Energy of photon= hv, or hc/λ

  8. Max Planck • 1858-1947 • Studied the light emitted by heated objects and that this energy is quantized. • Matter absorbs energy in whole number multiples of hv

  9. Neils Bohr • Developed the quantum model for the hydrogen atom • Proposed that the H atom had only certain energy states • Ground state- the lowest allowable energy state of an atom (1st energy level) • Excited state- when an atom gains energy • Stated that the electron moves around the nucleus in only certain allowed circular motion  proven incorrect • The smaller the orbital- the lower the energy level

  10. Quantum Mechanical Model • Principal Quantum Number (n)- number assigned to each orbit (page 147) • n=1 • Closest orbital to the nucleus • n=2 • The next orbital

  11. The movement of electrons around the nucleus is not completely understood now. Evidence indicates that they do not travel in circular orbitals.

  12. Louis de Broglie • Questioned whether particles of matter can behave like waves • de Broglie equation- predicts that all moving particles have wave like characteristics • λ =(h/mv) • m=mass, h=Planck’s constant, v=velocity, λ= wavelength

  13. Werner Heisenburg • 1901-1976 • Showed that it was impossible to take any measurement of an object without disturbing it

  14. Heisenburg Uncertainty Principle- it is impossible to know precisely both the velocity and position of a particle at the same time • You can’t assign fixed paths for electrons • The only thing that can be known is the probability that an electron is in a certain region around the nucleus

  15. Atomic orbital- 3D area around the nucleus that indicates an electron’s probable location • Principle Quantum Number(n)- indicates the size and energy of atomic orbitals

  16. Energy Sublevels- the number of sublevels increase as ‘n’ increases • Sublevels are labeled s,p,d,f. • S is spherical • P looks like a dumbbell • D & F don’t always have the same shape • n=1 (1 sublevel) • n=2 (2 sublevels) • n=3 (3 sublevels) and so forth

  17. s holds 2 electrons • p holds 6 electrons • d holds 10 electrons • f holds 14 electrons

  18. Draw diagonal through to show the sublevels fill

  19. Ground State Electron Configuration • the most stable, lowest energy arrangement of electrons • Electron configuration- the arrangement of electrons in an atom • Lower energy levels are more stable than higher energy levels • Electrons typically arrange themselves so the atom is in the lowest energy state

  20. Aufbau Principle- each electron occupies the lowest energy level available • Pauli Exclusion Principle- only 2 electrons can occupy a single orbital and they must have opposite spins • Hund’s Rule- single electrons with the same spin must occupy each equal energy level before adding electrons with opposite spins

  21. Electron Configuration Notation- 1s22s22p3 • A noble gas can be used in brackets and then the rest of the electron configuration used • [Ne]3s2 • There are exceptions to the aufbau principle where there are only partial filled shells such as Cu (page 160)

  22. Valence Electrons • Determine the chemical properties of an atom • The electrons in the outermost shell • Involved in forming chemical bonds • S is [Ne]3s23p4 • It has 6 electrons in it’s outer shell • Electron dot structure- contains the symbol for the atom surrounded by the valence electrons

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