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Shielding & Atomic Radius, Ions & Ionic Radius Chemistry AP - - PowerPoint PPT Presentation
Shielding & Atomic Radius, Ions & Ionic Radius Chemistry AP - - PowerPoint PPT Presentation
Shielding & Atomic Radius, Ions & Ionic Radius Chemistry AP Periodic Table Periodic Table Elements in same column have similar properties Column # (IA-VIIIA) gives # valence electrons All elements in column end in same ns x np y
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Periodic Table
Elements in same column have similar properties Column # (IA-VIIIA) gives # valence electrons All elements in column end in same nsx npy configuration
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Periodic Table
Elements in same column have similar properties Column # (IA-VIIIA) gives # valence electrons All elements in column end in same nsx npy configuration Ion Formation Metals lose electrons to form noble gas core: Na → Na+ + e–: [Ne]3s1 → [Ne] Al → Al3+ + 3e–: [Ne]3s23p1 → [Ne]
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Periodic Table
Elements in same column have similar properties Column # (IA-VIIIA) gives # valence electrons All elements in column end in same nsx npy configuration Ion Formation Metals lose electrons to form noble gas core: Na → Na+ + e–: [Ne]3s1 → [Ne] Al → Al3+ + 3e–: [Ne]3s23p1 → [Ne] Nonmetals gain electrons to form next noble gas: F + e– → F: 1s22s22p5 → 1s22s22p6 or [Ne] Se + 2e– → Se2–: [Ar]4s23d104p4 → [Ar]4s23d104p6 or [Kr]
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Special Ion Formation Transition metals lose ns2 electrons before (n–1)dx: Fe → Fe3+ + 3e–: [Ar]4s23d6 → [Ar]3d5 Ni → Ni2+ + 2e–: [Ar]4s23d8 → [Ar]3d8 Populated (n–1)d orbitals shield ns electrons, ns higher in energy, easier to remove Will see evidence in 2nd lesson from now
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Special Ion Formation Transition metals lose ns2 electrons before (n–1)dx: Fe → Fe3+ + 3e–: [Ar]4s23d6 → [Ar]3d5 Ni → Ni2+ + 2e–: [Ar]4s23d8 → [Ar]3d8 Populated (n–1)d orbitals shield ns electrons, ns higher in energy, easier to remove Will see evidence in 2nd lesson from now Post-transition metals can lose ns2 npx or just npx electrons: Sn → Sn2+ + 2e–: [Kr]5s24d105p2 → [Kr]5s24d10 Sn → Sn4+ + 4e–: [Kr]5s24d105p2 → [Kr]4d10 Full (n–1)d10 called “pseudo-noble gas” configuration
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Effective Nuclear Charge
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Effective Nuclear Charge
Outermost (valence) electrons shielded from full nuclear charge (Z) by inner core electrons: Trade-off between coulombic attraction to nucleus and repulsion by core electrons
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Effective Nuclear Charge
Outermost (valence) electrons shielded from full nuclear charge (Z) by inner core electrons: Trade-off between coulombic attraction to nucleus and repulsion by core electrons In all elements in energy levels n≥2, the effective nuclear charge, Zeff, is approximated by: Zeff = Z – σ σ is the shielding factor, repulsion by core electrons σ = number of core electrons Not exact; qualitative understanding of the phenomenon
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Trends in Zeff
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Within a period, Zeff increases as Z increases across and σ remains constant:
Trends in Zeff
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Within a period, Zeff increases as Z increases across and σ remains constant:
Trends in Zeff
σ = 0 σ = 2 σ = 10
Z = 1+ Z = 2+ Z = 3+ Z = 4+ Z = 5+ Z = 6+ Z = 7+ Z = 8+ Z = 9+ Z = 10+ Z = 11+ Z = 12+ Z = 13+ Z = 14+ Z = 15+ Z = 16+ Z = 17+ Z = 18+
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Within a period, Zeff increases as Z increases across and σ remains constant:
Trends in Zeff
Zeff=1+ Zeff=2+ Zeff=3+ Zeff=4+ Zeff=5+ Zeff=6+ Zeff=7+ Zeff=8+ Zeff=2 σ = 0 σ = 2 σ = 10
Z = 1+ Z = 2+ Z = 3+ Z = 4+ Z = 5+ Z = 6+ Z = 7+ Z = 8+ Z = 9+ Z = 10+ Z = 11+ Z = 12+ Z = 13+ Z = 14+ Z = 15+ Z = 16+ Z = 17+ Z = 18+
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Within a period, Zeff increases as Z increases across and σ remains constant: Within a group, Zeff remains constant as Z and σ both increase as n increases
Trends in Zeff
Zeff=1+ Zeff=2+ Zeff=3+ Zeff=4+ Zeff=5+ Zeff=6+ Zeff=7+ Zeff=8+ Zeff=2 σ = 0 σ = 2 σ = 10
Z = 1+ Z = 2+ Z = 3+ Z = 4+ Z = 5+ Z = 6+ Z = 7+ Z = 8+ Z = 9+ Z = 10+ Z = 11+ Z = 12+ Z = 13+ Z = 14+ Z = 15+ Z = 16+ Z = 17+ Z = 18+
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Within a period, Zeff increases as Z increases across and σ remains constant: Within a group, Zeff remains constant as Z and σ both increase as n increases Zeff = #Valence Electrons (outermost electrons with greatest n)
Trends in Zeff
Zeff=1+ Zeff=2+ Zeff=3+ Zeff=4+ Zeff=5+ Zeff=6+ Zeff=7+ Zeff=8+ Zeff=2 σ = 0 σ = 2 σ = 10
Z = 1+ Z = 2+ Z = 3+ Z = 4+ Z = 5+ Z = 6+ Z = 7+ Z = 8+ Z = 9+ Z = 10+ Z = 11+ Z = 12+ Z = 13+ Z = 14+ Z = 15+ Z = 16+ Z = 17+ Z = 18+
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Atomic Radius
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Radius is smallest where Zeff is largest, increases to left as Zeff decreases Electron attraction depends on Zeff Stronger attraction pulls electrons closer to nucleus Electron cloud, radius smaller
Atomic Radius
Radius Increases
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Radius is smallest where Zeff is largest, increases to left as Zeff decreases Electron attraction depends on Zeff Stronger attraction pulls electrons closer to nucleus Electron cloud, radius smaller Radius increases as n increases Electrons in higher energy levels more shielded, farther from nucleus Electron orbitals larger, radius larger
Atomic Radius
Radius Increases Radius Increases
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Periodic Variation in Radius
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Periodic Variation in Radius
Atoms exhibit trends in radius from period to period:
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Ionic Radius
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Ionic Radius
Metals lose electrons: Na → Na+ + e– positive ion smaller than atom: less electron-electron repulsion, remaining electrons experience more electrostatic attraction to nucleus
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Ionic Radius
Metals lose electrons: Na → Na+ + e– positive ion smaller than atom: less electron-electron repulsion, remaining electrons experience more electrostatic attraction to nucleus Nonmetals gain electrons: Cl + e– → Cl– negative ion larger than atom: more electron-electron repulsion, electrons experience less electrostatic attraction to nucleus
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Ionic Radius
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Ionic Radius
Ionic radius increases down group same trend as atomic radius
- uter electrons more shielded,
less attracted to nucleus
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Ionic Radius
Negative Ions Positive Ions
Ionic radius increases down group same trend as atomic radius
- uter electrons more shielded,
less attracted to nucleus Ionic radius increases right-to-left Split at anion/cation boundary Anions filling higher energy level than cations
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Isoelectronic Ions
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Isoelectronic Ions
In isoelectronic series, all ions have same electron configuration
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Isoelectronic Ions
In isoelectronic series, all ions have same electron configuration
[Ne] [Ar] [Xe]
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Isoelectronic Ions
In isoelectronic series, all ions have same electron configuration radius decreases as Z (hence Zeff) increases Stronger electrostatic attraction with same number of electrons
[Ne] [Ar] [Xe]