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Bohr Model

Electronic Structure of Atoms 6.4 The Wave Behavior of Matter 6.5 Quantum Mechanics and Atomic Orbitals 6.6 Representation of Orbitals. Bohr Model Each energy level can contain more than 1 electron  But the max # for each level is different

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Bohr Model

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  1. Electronic Structure of Atoms6.4 The Wave Behavior of Matter6.5 Quantum Mechanics and Atomic Orbitals6.6 Representation of Orbitals

  2. Bohr Model • Each energy level can contain more than 1 electron But the max # for each level is different • Electrons fill in energy levels starting from lowest energy level to the next higher energy level • REMEMBER # Protons = # Electrons in a neutral atom • Example = oxygen

  3. 6.4 The Wave Behavior of Matter Louis de Broglie (1892-1987) • proposed if radiant energy (under appropriate conditions) could behave as a stream of particles and exhibit properties of wave could electrons orbiting nucleus behave as a wave λ= h / mv h = Planck’s constant 6.626 x 10-34 J/s m = mass v = velocity mv = momentum PRACTICE: What is the wavelength of an electron moving with a speed of 5.97 x 106 m/s? mass of e- =9.11 x 10-31 kg. 1 J =1 kg m2/s2

  4. Practice de Broglie’s hypo applicable to all matter any object of mass and velocity would have characteristics of a wave • Q. Calculate the velocity of a neutron whose de Broglie wavelength is 500 pm. mass of neutron= 1.67 x 10-27 kg λ= h / mv rearrange equation h = Planck’s constant 6.626 x 10-34 J/s m = mass v = velocity 6.626 x 10-34 kg m2/s2/s (5x10-10m)(1.67 x 10-27 kg) = 794 m/s or 7.92 x 102 m/s

  5. Wave properties of e- demonstrated experimentally… Electron diffraction • as electrons are passed though a crystal they are diffracted • stream of electrons exhibits similar kind of wave behavior as EM radiation • ex: technique used in electron microscope to obtain images at atomic scale (3,000,000 x magnification)

  6. The Uncertainty Principle If an e- exhibits wave properties, can we calculate the position, direction of motion, and speed at any time??? Werner Heisenberg (1901- 1976) Uncertainty Principle Impossible to know both the exact momentum and exact location of an electron simultaneously

  7. RESULT De Broglie’s hypo and Heisenberg’s Uncertainty Principle set stage for new approach to atomic structure model that describes energy of e- while describing probabilities of location

  8. 6.5 Quantum Mechanics and Atomic Orbitals Erwin Schrodinger (1887-1961) • Austrian physicist • proposed wave equation incorporates wave and particle behavior of e- = quantum mechanics or wave mechanics • Solving equation lead toWave functions- def. mathematical description of an allowed energy state (an orbital) for an e- • ex: Ψ Greek letter psi • Ψ2 provides info about e- location when in allowed energy state = probability density or electron density

  9. Orbitals • Def. wave function; space where there is a high probability that it is occupied by a pair of electrons; each orbital has a characteristic energy and shape

  10. Quantum Numbers1. Principal Quantum Number(n) • Indicates main energy levels n = 1, 2, 3, 4… • as n increases = orbital becomes larger  e spend more time farther from nucleus • as n increases = e- has higher energy and bound less tightly to nucleus • n determines the number of sublevels within the principle energy level

  11. 2. Angular Momentum Quantum Number (l) • l = n – 1 • shape of orbital Each main energy level has sub-levels= s, p, d, f

  12. 3. Magnetic Quantum Number (ml) • describes orientation of orbital in space • # of orbitals • equal to –l to +l ex: l = 3; then ml = -3,-2,-1,0,1,2,3

  13. Electron shell: all orbitals that have the same value of n • Subshell: set of orbitals that all have the same n and l values

  14. Ground State: when electrons occupy lowest energy orbital • Excited State: when electron occupies any other orbital; e- can be excited to higher-energy orbital by absorption of a photon of appropriate energy

  15. Sample Exercise • Predict the number of subshells in the fourth shell? • 4 • Give the label for each of these subshells • 4s, 4p, 4d, 4f • How many orbitals are in each of theses subshells? • 4s=1 (l=0 ml=0) 4p=3 (l=1 ml=-1,0,1) • 4d=5 (l=2 ml=-2,-1,0,1,2) 4f =7

  16. 6.6 Representation of Orbitals S orbital: spherical, 1 subshell Radial Probability Density probability of finding an e- at specific distance from nucleus node: intermediate point where probability goes to 0 as n increases =size of orbital increases = increase in distance from nucleus

  17. p Orbital • dumbbell shaped, 2 lobes • ml = 3 possible values, -1,0,1 • p size increases as move from 2p to 3p etc

  18. d and f Orbitals d= four leaf clover shape orbitals • five 3d orbitals, five 4d orbitals etc • ml= -2,-1,0,1,2 f= complicated shape • seven 4d orbitals, 5d • ml = -3,-2,-1,0,1,2,3

  19. Electron Spin • e- behave as tiny sphere spinning on own axis 4. Spin Magnetic Quantum Number (ms) s = spin +1/2 (clockwise) or -1/2 (counterclockwise)

  20. Electron Configuration • The arrangement of electrons in an atom around nucleus • Ex: Hydrogen = 1s1 • Ex: Helium = 1s2

  21. Orbitals in Sublevels Sublevel # Orbitals # electrons s 1 2 p 3 6 d 5 10 f 7 14

  22. Standard Notation of Fluorine Number of electrons in the sub level 2,2,5 1s22s22p5 Main Energy Level Numbers 1, 2, 2 Sublevels

  23. Three rules are used to build the electron configuration: • Aufbau principle • Pauli Exclusion Principle • Hund’s Rule

  24. Aufbau Principle • Electrons occupy orbitals of lower energy first.

  25. Pauli Exclusion Principle • no 2 e- in an atom can have the same 4 QN • An orbital can hold only two electrons and they must have opposite spin.

  26. Hund’s Rule In a set of orbitals, the electrons will fill the orbitals in a way that would give the maximum number of parallel spins (maximum number of unpaired electrons). Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

  27. Orbital Diagram (Box Diagram) • Diagram in which orbitals are represented by boxes grouped by sublevels with arrows indicating electrons

  28. Aufbau Diagram for Hydrogen

  29. Aufbau Diagram for Helium

  30. Aufbau Diagram for Lithium

  31. Aufbau Diagram for Beryllium

  32. Aufbau Diagram for Boron

  33. Aufbau Diagram for Carbon

  34. Aufbau Diagram for Nitrogen

  35. Aufbau Diagram

  36. Aufbau Diagram for Fluorine

  37. Shorthand Notation • Use the last noble gas that is located in the periodic table right before the element. • Write the symbol of the noble gas in brackets. • Write the remaining configuration after the brackets. • Ex: Fluorine: [He] 2s2 2p5

  38. Blocks in the Periodic Table

  39. HOMEWORK • Complete WS

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