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Unit 6B: Atomic Structure and Bonding Theory

Unit 6B: Atomic Structure and Bonding Theory. By Lauren and Joe. Electromagnetic Spectrum. From www.lcse.umn.edu/specs/labs/images/spectrum.gif. Electromagnetic Spectrum. Frequency and wavelength are inversely related, as demonstrated by the equation c=λν

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Unit 6B: Atomic Structure and Bonding Theory

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  1. Unit 6B: Atomic Structure and Bonding Theory By Lauren and Joe

  2. Electromagnetic Spectrum From www.lcse.umn.edu/specs/labs/images/spectrum.gif

  3. Electromagnetic Spectrum • Frequency and wavelength are inversely related, as demonstrated by the equation c=λν • c-speed of light constant-2.9979x108m/s • λ-wavelength(m) • ν-frequency(Hz or s-1)

  4. Quantum Theory • Einstein—Light behaves as if it consists of quantized energy packets, meaning that energy can have only certain allowed values given by the equation Ephoton=hν • Ephoton-(J) • h-Planck’s constant-6.626x10-34 J-sec • ν-frequency (Hz or s-1)

  5. Another Equation to Remember Ephoton=Eremove electron/threshold + Ekinetic

  6. Quantum Numbers • n-principal quantum number (shell) • i.e. 3s, n=3 • l-azimuthal quantum number (sub-shell) • The value of l corresponds to the sub-shell of the orbital • s=0, p=1, d=2, f=3 • i.e. if n=3, can have 3s, 3p, 3d. Accordingly, you can have l values 0, 1, and 2.

  7. More Quantum Numbers! • ml-magnetic quantum number • Each orbital has number from –L to +L • i.e. 3p4 , occupies 1st orbital, ml= -1 • ms-magnetic spin quantum number • Value is ±1/2 • If electron points up, +1/2 • If electron points down, -1/2 • i.e. 3p4, points down, ms= -1/2

  8. DeBroglie Wavelength • Matter has a characteristic wavelength that depends on its momentum, mv λ=h/mv • λ-wavelength(m) • h-Planck’s constant-6.626x10-34 J-s • m-mass of particle(kg) (e-=9.11x10-31kg) • v-velocity (m/s)

  9. Bohr’s Model • A model of the hydrogen atom that explains its line spectrum • Light emitted when the electron drops from a higher energy state to a lower energy state • Light must be absorbed to excite the electron from a lower energy state to a higher energy state

  10. Electron Configuration • Use the periodic table to write electron configurations • Core electron configuration—use largest noble gas that is smaller than atom/ion, then write additional electrons • Remember that each orbital can hold 2 electrons each • Place 1 electron in each orbital before putting a second one • Electron configurations are most stable when the orbitals are full or half-full

  11. Electron Configuration • D Block (Transition metals) • -5 orbitals @ 2 electrons each=10 electrons • D block 1 behind s/p block • F Block • 7 orbitals @2 electrons each=14 electrons • F block 1 behind D block, 2 behind s/p block

  12. Electron Configuration of Ions • When determining configurations for cations, remove electrons first from the orbital with the largest quantum number n • For example, Sn=[Ar] 4s23d104p2 Sn3+= =[Ar]4s13d10

  13. Hybridization • Mixing of s, p, and d orbitals to form hybrid orbitals • A particular mode of hybridization corresponds with each of the five common electron-domain geometries • note: electron domain geometry is arrangement of electron domains around a central atom. Each bond, whether it is single, double, or triple, and each lone pair is one electron domain.

  14. Hybridization • Linear-2 electron domains-sp hybridization • Trigonal planar-3 electron domains- sp2 • Tetrahedral-4 domains, sp3 • Trigonal bipyramidal- 5 domains, sp3d • Octahedral- 6 domains, sp3d2

  15. Valence Bond Theory • Bonds form when atomic orbitals overlap between two atoms • The greater the overlap between two orbitals, the stronger the bond • Sigma Bond • Covalent bonds formed from end to end overlap of s orbitals • Pi Bond • Bond formed from the sideways overlap of p orbitals

  16. Molecular Orbital Theory • Electrons exist in allowed energy states called molecular orbitals (MOs) • Like an atomic orbital, an MO can hold two electrons of opposite spin • Occupation of bonding MOs favors bond formation • Occupation of antibonding MOs (denoted with an *) is unfavorable

  17. Molecular Orbital Theory • Bond Order • Bond Order = ½(# of electrons bonding - # of electrons anti-bonding) • The principle of anti-bonding sets molecular orbital theory apart from valence bond theory

  18. Paramagnetism and Diamagnetism • paramagnetism—an attraction of a molecule by a magnetic field due to unpaired electrons • diamagnetism—a weak repulsion from a magnetic field by paired electrons

  19. Unit 6B: Test your knowledge!

  20. Question 1 What is the core electron configuration of Pb3+?

  21. Answer [Xe]6s14f145d10

  22. Question 2 What type of hybridization does the central atom in the following compounds assume? • NH3 • SF6 • ClF3

  23. Answers • a. Sp3 • b. Sp3d2 • c. Sp3d

  24. Final Question! • What score will you get on the AP Chem Exam after seeing this presentation?

  25. ANSWER 5

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