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Electrons & Energy

Electrons & Energy

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Electrons & Energy

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  1. Electrons & Energy

  2. Chemistry 12-5 • Aim: How do we know where an electron is? How do we illustrate where electrons are? • Do Now: How many electrons does Lithium have? Sodium? HW: • Complete Firework reading & questions for Friday 12/7 • Lab 7 due Friday 12/7

  3. 1- Main features of Bohr Model • Atom has dense positively charged nucleus • Electrons are in fixed paths around the nucleus • Electrons have a specific amount of energy (quantized)

  4. Problems with Bohr Model • When viewing emission spectra of Hydrogen (which has one electron) the bright line spectra fits his model that an electron has a fixed path. Bohr’s Experiment Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 76

  5. BUT with more than 1 electron… • Bohr’s model no longer fits- bright line spectra of various wavelengths emerge, leading one to believe electrons do not have FIXED positions but rather MOVE AROUND within and about orbitals.

  6. 1- Orbitals • Region of space about nucleus with highest probability of finding an electron. 2- Wave mechanical model • Electrons do not orbit the nucleus in definite fixed pathways. • Electrons are in orbitals– regions where electrons are found- not fixed distances • Electrons have distinct amounts of energy

  7. Venn Diagram of Bohr vs Wave mechanical Model • Take what you learned in last few slides and reading from text and passage to create a venn diagram of these 2 atomic models. Wave mechanical Bohr both

  8. Orbitals & Valence electrons

  9. 1- Orbitals • Region of space about nucleus with highest probability of finding an electron. 2- Wave mechanical model • Electrons do not orbit the nucleus in definite fixed pathways. • Electrons are in orbitals– regions where electrons are found- not fixed distances • Electrons have distinct amounts of energy

  10. How We Discuss Electrons Electrons “orbit” around the nucleus of the atom according to very specific rules. • We will make fun of these rules by calling them the “electron (e-) jogging” Rules: • Maximum of two e- per jogging track (i.e. “orbitals”) • Easier orbitals fill up first.

  11. s Orbital (flat and level): p Orbital (Rolling Hills): d Orbital (Steep Hills):

  12. 2s orbital (1 of these, 2 e–) 2p orbitals (3 of these, 6 e–) 1s orbital (1 of these, 2 e–) 3s orbital (1 of these, 2 e–) 3p orbitals (3 of these, 6 e–)

  13. More Jogging Rules • 3. All orbitals of equal difficulty must have one e- before any double up. • 4. e- on the same orbital must go opposite ways (2 e-’s fit on each orbital)

  14. Electron VOCAB • Valence shell: outermost shell in an atom • Valence electrons: the electrons located in the outermost shell of the atom • Core electrons: All other electrons in an atom besides the valence electrons. • Kernel: the nucleus AND the core electrons

  15. Arrangement of electrons in their shells is highly predictable • Atomic number is the same as the total number of electrons • The period (row) number of the element is the same as the # of electron shells. • For main group elements, the group number (columns) of the element is the same as the # of valence electrons (those in the outermost shell).

  16. Period # = # of electron shells (total)

  17. Group # = # of valence electrons

  18. 2s 3s 2p 3p 3d 1s A Cross Section of an Atom n0 p+ Rings of Saturn The first ionization energy level has only one sublevel (1s). The second energy level has two sublevels (2s and 2p). The third energy level has three sublevels (3s, 3p, and 3d). Although the diagram suggests that electrons travel in circular orbits, this is a simplification and is not actually the case. Corwin, Introductory Chemistry2005, page 124

  19. Maximum Capacities of Subshells and Principal Shells n 1 2 3 4 ...n l 0 0 1 0 1 2 0 1 2 3 Subshell designation s s p s p d s p d f Orbitals in subshell 1 1 3 1 3 5 1 3 5 7 Subshell capacity 2 2 6 2 6 10 2 6 10 14 Principal shell capacity 2 8 18 32 ...2n2 Hill, Petrucci, General Chemistry An Integrated Approach1999, page 320

  20. Electron Orbitals: Electron orbitals Equivalent Electron shells (a) 1s orbital (b) 2s and 2p orbitals c) Neon Ne-10: 1s, 2s and 2p 1999, Addison, Wesley, Longman, Inc.

  21. Feeling overwhelmed? Chemistry “Teacher, may I be excused? My brain is full." Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  22. Writing Electron Configurations Where are the e-’s? (probably

  23. 4f 4d n = 4 4p 3d 4s n = 3 3p 3s 2p n = 2 2s 1s n = 1 Sublevels Energy

  24. 4f 4d s n = 4 p d f s p d 4p s p 3d s 4s n = 3 3p 3s 2p n = 2 2s 1s n = 1 Sublevels Energy 1s22s22p63s23p64s23d104p65s24d10…

  25. The Bottom Line Two electrons fit on the first energy level Eight electrons fit on the second (2 then 6) Eighteen fit on the third (2 then 6, first 2 on the fourth, then the last 10) Eighteen fit on the fourth (2 before last 10 on third, then 6, first 2 on the fifth, then the last 10) Things can get really strange after that. Your Periodic Table will help you out.

  26. H He Li N Al Ti As Xe 1s1 1s2 1s2 2s1 1s2 2s2 2p3 1s2 2s2 2p6 3s2 3p1 1s2 2s2 2p6 3s2 3p6 4s2 3d2 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 You Try:

  27. Filling Rules for Electron Orbitals Aufbau Principle: Electrons are added one at a time to the lowest energy orbitals available until all the electrons of the atom have been accounted for. Pauli Exclusion Principle: An orbital can hold a maximum of two electrons. To occupy the same orbital, two electrons must spin in opposite directions. Hund’s Rule: Electrons occupy equal-energy orbitals so that a maximum number of unpaired electrons results. *Aufbau is German for “building up”

  28. General Rules 6d Aufbau Principle • Electrons fill the lowest energy orbitals first. • “Lazy Tenant Rule” 5f 6d 7s 5f 6p 7s 5d 6p 4f 6s 5d 4f 5p 6s 4d 5p 5s 4d 4p 5s 3d 4p 4s 3d 4s 3p Energy 3p 3s 3s 2p 2p 2s 2s 1s 1s Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  29. General Rules • Pauli Exclusion Principle • Each orbital can hold TWO electrons with opposite spins. Wolfgang Pauli Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  30. General Rules • Hund’s Rule • Within a sublevel, place one electron per orbital before pairing them. • “Empty Bus Seat Rule” RIGHT WRONG Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  31. Energy Level Diagram N Lanthanum 6s 6p 5d 4f Bohr Model 5s 5p 4d 4s 4p 3d Arbitrary Energy Scale 3s 3p 2s 2p 1s Electron Configuration La = 1s22s22p63s23p64s23d6 4s23d104p65s24d105p66s25d1 NUCLEUS HHeLiCNAlArFFeLa CLICK ON ELEMENT TO FILL IN CHARTS

  32. 8 O 15.9994 2s 2p 1s Notation • Orbital Diagram O 8e- • Electron Configuration 1s22s22p4 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  33. Order in which subshells are filled with electrons 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 6d 4f 5f 2 2 6 2 6 2 10 6 2 10 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d …

  34. In General, as energy level # increases Electrons… Have more Energy! AND Are farther from the Nucleus!

  35. Kernel Electrons: The electrons in the inner energy levels, close to the nucleus Valence Electrons: The electrons in the outer energy levels Involved in Chemical Bonding!

  36. He = 2 Ne = 2-8 Ar = 2-8-8 Kr = 2-8-18-8 2 valence electrons 8 valence electrons 8 valence electrons 8 valence electrons How many Valence?

  37. 16 S 32.066 Core Electrons Valence Electrons Notation • Longhand Configuration S 16e- 2p6 2s2 1s2 3s2 3p4 • Shorthand Configuration S 16e- [Ne]3s2 3p4 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  38. The Octet Rule Most atoms “want” a valence shell with eight electrons: NOT H, He, Li, Be, B Nobel gas atoms (group 18) have full valence shells. They are stable, low-energy and unreactive. Other atoms try to become like noble gas atoms by giving away or acquiring electrons.

  39. Hydrogen 1H Helium 2He Nitrogen 7N Lithium 3Li Beryllium 4Be Boron 5B Carbon 6C Oxygen 8O Fluorine 9F Neon 10Ne Phosphorous 15P Sodium 11Na Magnesium 12Mg Aluminum 13Al Silicon 14Si Sulfur 16S Chlorine 17Cl Argon 18Ar Electron Configurations of First 18 Elements:

  40. Fluorine, F Has 9 protons and 9 electrons How many valence? 7 2 options: lose 7 or gain 1 Which is easier? What is a common flourine ion? F1-

  41. Chlorine Has 17 protons and 17 electrons How many valence? 7 2 options: lose 7 or gain 1 Which is easier? What is a common flourine ion? Cl1-

  42. Lithium Has 3 protons and 3 electrons How many valence? 1 2 options: lose 1 or gain 7 Which is easier? What is a common flourine ion? Li1+

  43. Sodium Has 3 protons and 3 electrons How many valence? 1 2 options: lose 1 or gain 7 Which is easier? What is a common flourine ion? Na1+