lecture18 (11-13-2006) Ch 9

lecture18 (11-13-2006) Ch 9 - Chemistry 2A-c F2006...

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1 PERIODIC TRENDS Mendeleev and Meyer (1869): When elements are arranged in increasing atomic mass , certain sets of properties recur periodically Some trends in experimentally determined properties: IONIZATION ENERGIES ELECTRON AFFINITIES ATOMIC RADII IONIC RADII Chemistry 2A Chemistry 2A -c F2006 c F2006 (Ch9 (Ch9 -1)178 1)178 The Periodic Table and some Atomic Properties The Periodic Table and some Atomic Properties Atomic Number
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2 TRENDS IN ATOMIC RADII FOR GROUPS 1,2 and 13 to 18 hy? Orbitals bigger as n increases Radial probability density extends further ATOMIC RADIUS Atomic radii increase down the group Chemistry 2A Chemistry 2A -c F2006 c F2006 (Ch9 (Ch9 -2)179 2)179
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3 TRENDS IN ATOMIC RADII FOR GROUPS 1,2 and 13 to 18 Why? The inner electrons do not screen the nucleus. ATOMIC RADIUS ATOMIC RADIUS Atomic radii decrease across a period Chemistry 2A Chemistry 2A -c F2006 c F2006 (Ch9 (Ch9 -3)180 3)180
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4 Electron SCREENING AND PENETRATION PENETRATION Is to get close to the nucleus SCREENING Is to block the view of other electrons of the nucleus Example: Consider the excited state of helium 1s 1 3p 1 LOOK AT RADIAL PROBABILITY DISTRIBUTIONS Chemistry 2A Chemistry 2A -c F2006 c F2006 (Ch9 (Ch9 -4)181 4)181
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5 0 0.1 0.2 0.3 0.4 0.5 0.6 0 5 10 15 20 25 30 SCREENING AND PENETRATION Is THE 1s close to the nucleus PENETRATES WELL SEES A CHARGE OF Z=2 EFFECTIVE NUCLEAR CHARGE…. .. 3p THE 3p DOES NOT SCREEN THE NUCLEUS Chemistry 2A Chemistry 2A -c F2006 c F2006 (Ch9 (Ch9 -5)182 5)182 # of nodes in radial wavefunctions: n- l -1
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6 0 0.1 0.2 0.3 0.4 0.5 0.6 0 5 10 15 20 25 30 SCREENING AND PENETRATION EFFECTIVE NUCLEAR CHARGE Is 3p Z eff = Z - S S = average # of electrons responsible for screening FOR THE 1s orbital. .
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This note was uploaded on 04/23/2008 for the course CHEM 2A taught by Professor Guo during the Fall '08 term at UC Davis.

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lecture18 (11-13-2006) Ch 9 - Chemistry 2A-c F2006...

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