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What’s coming up???

What’s coming up???. Oct 25 The atmosphere, part 1 Ch. 8 Oct 27 Midterm … No lecture Oct 29 The atmosphere, part 2 Ch. 8 Nov 1 Light, blackbodies, Bohr Ch. 9 Nov 3,5 Postulates of QM, p-in-a-box Ch. 9 Nov 8,10 Hydrogen and multi – e atoms Ch. 9 Nov 12 Multi-electron atoms Ch.9,10

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What’s coming up???

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  1. What’s coming up??? • Oct 25 The atmosphere, part 1 Ch. 8 • Oct 27 Midterm … No lecture • Oct 29 The atmosphere, part 2 Ch. 8 • Nov 1 Light, blackbodies, Bohr Ch. 9 • Nov 3,5 Postulates of QM, p-in-a-box Ch. 9 • Nov 8,10 Hydrogen and multi – e atoms Ch. 9 • Nov 12 Multi-electron atoms Ch.9,10 • Nov 15 Periodic properties Ch. 10 • Nov 17 Periodic properties Ch. 10 • Nov 19,22 Valence-bond; Lewis structures Ch. 11 • Nov 24 Hybrid orbitals; VSEPR Ch. 11, 12 • Nov 26 VSEPR Ch. 12 • Nov 29 MO theory Ch. 12 • Dec 1 MO theory Ch. 12 • Dec 2 Review for exam

  2. SCREENING AND PENETRATION PENETRATION Is to get close to the nucleus SCREENING Is to block the view of other electrons of the nucleus LOOK AT RADIAL PROBABILITY DISTRIBUTIONS

  3. In a multi-electron atom Zeff(s) > Zeff(p) > Zeff(d) ENERGY LEVELS REVERSE!! E4s < E3d S-orbital penetrates closer to nucleus

  4. Closer proximity to nucleus  Higher effective nuclear charge, Zeff

  5. 4d 5s 4p 3d 4s 3p E 3s 2p 2s 1s The result is that 4s lies below 3d

  6. 1s 2s 2p Ne 1s22s22p6 MAGNETIC PROPERTIES Atoms, molecules or ions with all electrons paired are diamagnetic. Diamagnetic materials are weakly repelled by magnetic fields NEON Example: ALL ELECTRONS PAIRED

  7. Spin quantum number Electrons are influenced by a magnetic field as though they were spinning charges. They are not really, but we think of them as having “spin up” or “spin down” levels.

  8. 1s 2s 2p N 1s22s22p3 MAGNETIC PROPERTIES Atoms, molecules or ions with at least one unpaired electron are paramagnetic. Paramagnetic materials are strongly attracted to magnetic fields. Nitrogen atom is PARAMAGNETIC

  9. Which of these is paramagnetic? • Na Ca • K+ O2-

  10. PERIODIC TRENDS We will look at some trends in experimentally determined properties such as: ATOMIC RADII IONIC RADII IONIZATION ENERGIES ELECTRON AFFINITIES

  11. TRENDS IN ATOMIC RADII FOR GROUPS 1,2 and 13 to 18 Atomic radii increase down the group ATOMIC RADIUS ATOMIC RADIUS Orbitals bigger as n increases Radial probability density extends further.

  12. TRENDS IN ATOMIC RADII FOR GROUPS 1,2 and 13 to 18 Atomic radii decrease across a period ATOMIC RADIUS ATOMIC RADIUS ATOMIC RADIUS

  13. SCREENING AND PENETRATION ATOMIC RADIUS DECREASES ACROSS PERIOD! WHY? AS WE ADD ELECTRONS The electrons go into same shell and do not screen the nucleus from each other As nuclear charge goes up, so does Zeff Therefore radial probability pulled in….

  14. Zeff increases .. no screening .. radius decreases

  15. 1 18 1 2 3 4 5 6 7 1s 1s 2 13 14 15 16 17 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p La 6s 5d 6p Ac 6d 7s 4f 5f Zeff INCREASES RADIUS DECREASES DOWN GROUP...

  16. 1 18 1 2 3 4 5 6 7 1s 1s 2 13 14 15 16 17 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p La 6s 5d 6p Ac 6d 7s 4f 5f RADIUS INCREASES Zeff DECREASES

  17. TRENDS IN IONIC RADII FOR GROUPS 1,2 and 13 to 18 IONIC RADIUS IONIC RADIUS IONIC RADIUS Same reasons as for atomic radii……. Cations and anions…...

  18. Cations are smaller than their corresponding neutral atoms. Na is 186 pm and Na+ is 95 pm One less electron electrons pulled in by nuclear charge Anions are larger than their corresponding neutral atoms. F is 64 pm and F- is 133 pm same nuclear charge and repulsion among electrons increases radius O < O– < O2– QUESTIONS…...

  19. EXAMPLES Which is bigger? Rb …. higher n, bigger orbitals Na or Rb K …. poorer screening for Ca K or Ca Ca or Ca2+ Ca …. bigger than cation Br or Br- Br …. smaller than anion ISOELECTRONIC SPECIES? What about

  20. QUESTION The species F-, Na+,Mg2+ have relative sizes in which order? ALL 1s22s22p6 1 F-< Na+<Mg2+ ALL are isoelectronic 2 F-> Na+>Mg2+ 3 Na+>Mg2+> F- 4 Na+=Mg2+= F- 5 Mg2+> Na+>F-

  21. QUESTION The species F-, Na+,Mg2+ have relative sizes in which order ? 1 F-< Na+<Mg2+ 2 F-> Na+>Mg2+ Check numbers 3 Na+>Mg2+> F- Na+ is 95 pm Mg2+ is 66 pm 4 Na+=Mg2+= F- F- is 133 pm 5 Mg2+> Na+>F-

  22. ELECTRON AFFINITY the energy change associated with the addition of an electron to a gaseous atom. X + e– X– F(g) + e– F–(g) DE= -328 kJmol-1 TWO DEFINITIONS! the electron affinity is negative if DE<0. EA = DE the electron affinity is positive if DE<0. EA = -DE In general no clear cut trends…….

  23. TRENDS IN EA ELECTRON AFFINITY ELECTRON AFFINITY MORE NEGATIVE MORE NEGATIVE ELECTRON AFFINITY MORE NEGATIVE

  24. ELECTRON AFFINITIES What is special about … He, Ne and Ar? Be, N and Mg?

  25. He, Ne, Ar: rare gases … adding electron to filled shell … must increase n • Be, Mg: alkali earths … adding electron to filled sub-shell … must increase l • N: Hund’s rule stability… adding electron to ½-filled degenerate p-shell • Q: what would you predict for… Cr, Fe?

  26. TRENDS IN IONIZATION ENERGIES M(g) M+(g) + e- The ionization energy of gaseous atoms of the elements have been measured…. And we find…….

  27. TRENDS IN FIRST IE First Ionization energies decrease down the group Zeff DECREASES IONIZATION ENERGY IONIZATION ENERGY Zeff INCREASES UP THE GROUP Electrons closer to nucleus more tightly held

  28. TRENDS IN FIRST IE Zeff INCREASES IONIZATION ENERGY IONIZATION ENERGY Greater effective nuclear charge across period Poor shielding by electrons added

  29. TRENDS IN FIRST IE

  30. Closed shells most stable The noble gases have the highest ionization energy!

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