10-13-08%20-%20Lecture%207%20-%20Chapter%201

10-13-08%20-%20Lecture%207%20-%20Chapter%201 - PERIODIC...

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Unformatted text preview: PERIODIC PERIODIC TRENDS TRENDS General Periodic Trends General Periodic Trends • Atomic and ionic size • Ionization energy • Electron affinity Higher effective nuclear charge Electrons held more tightly Larger orbitals. Electrons held less tightly. Effective Nuclear Charge, Z Effective Nuclear Charge, Z eff eff • Z eff is the nuclear charge experienced by the outermost electrons. • Explains why E(2s) < E(2p) • Z eff increases across a period owing to incomplete shielding by inner electrons. • Estimate Z eff by [ Z - (no. inner electrons) ] • Charge felt by 2s e- in Li Z* = 3 - 2 = 1 • Be Z* = 4 - 2 = 2 • B Z* = 5 - 2 = 3 and so on! Variation of Z Variation of Z eff eff with Atomic Number (Z) with Atomic Number (Z) Effective Nuclear Charge, Z Effective Nuclear Charge, Z eff eff • Atom Z eff Experienced by Electrons in Valence Orbitals • Li +1.28 • Be +1.91 • B +2.42 • C +3.14 • N +3.83 • O +4.45 • F +5.76 Increase in Increase in Z Z eff eff across a across a period period Valence electrons are screened by other electrons, especially by core electrons, but only incompletely. General Periodic Trends...
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10-13-08%20-%20Lecture%207%20-%20Chapter%201 - PERIODIC...

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