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 configuration

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 configuration Ion Formation Metals lose electrons to form noble gas core: Na → Na + + e – : [Ne]3s 1 → [Ne] Al → Al 3+ + 3e – : [Ne]3s 2 3p 1 → [Ne]

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 configuration Ion Formation Metals lose electrons to form noble gas core: Na → Na + + e – : [Ne]3s 1 → [Ne] Al → Al 3+ + 3e – : [Ne]3s 2 3p 1 → [Ne] Nonmetals gain electrons to form next noble gas: F + e – → F: 1s 2 2s 2 2p 5 → 1s 2 2s 2 2p 6 or [Ne] Se + 2e – → Se 2– : [Ar]4s 2 3d 10 4p 4 → [Ar]4s 2 3d 10 4p 6 or [Kr]

Special Ion Formation Transition metals lose ns 2 electrons before (n–1)d x : Fe → Fe 3+ + 3e – : [Ar]4s 2 3d 6 → [Ar]3d 5 Ni → Ni 2+ + 2e – : [Ar]4s 2 3d 8 → [Ar]3d 8 Populated (n–1)d orbitals shield ns electrons, ns higher in energy, easier to remove Will see evidence in 2 nd lesson from now

Special Ion Formation Transition metals lose ns 2 electrons before (n–1)d x : Fe → Fe 3+ + 3e – : [Ar]4s 2 3d 6 → [Ar]3d 5 Ni → Ni 2+ + 2e – : [Ar]4s 2 3d 8 → [Ar]3d 8 Populated (n–1)d orbitals shield ns electrons, ns higher in energy, easier to remove Will see evidence in 2 nd lesson from now Post-transition metals can lose ns 2 np x or just np x electrons: Sn → Sn 2+ + 2e – : [Kr]5s 2 4d 10 5p 2 → [Kr]5s 2 4d 10 Sn → Sn 4+ + 4e – : [Kr]5s 2 4d 10 5p 2 → [Kr]4d 10 Full (n–1)d 10 called “pseudo-noble gas” configuration

Effective Nuclear Charge

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

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, Z eff , is approximated by: 
 Z eff = Z – σ σ is the shielding factor, repulsion by core electrons σ = number of core electrons Not exact; qualitative understanding of the phenomenon

Trends in Z eff

Trends in Z eff Within a period, Z eff increases as Z increases across and σ remains constant:

Trends in Z eff Within a period, Z eff increases as Z increases across and σ remains constant: σ = 0 Z = 1+ Z = 2+ σ = 2 Z = 3+ Z = 4+ Z = 5+ Z = 6+ Z = 7+ Z = 8+ Z = 9+ Z = 10+ σ = 10 Z = 11+ Z = 12+ Z = 13+ Z = 14+ Z = 15+ Z = 16+ Z = 17+ Z = 18+

Trends in Z eff Within a period, Z eff increases as Z increases across and σ remains constant: σ = 0 Z = 1+ Z = 2+ Z eff =2 σ = 2 Z = 3+ Z = 4+ Z = 5+ Z = 6+ Z = 7+ Z = 8+ Z = 9+ Z = 10+ σ = 10 Z = 11+ Z = 12+ Z = 13+ Z = 14+ Z = 15+ Z = 16+ Z = 17+ Z = 18+ Z eff =1+ Z eff =2+ Z eff =3+ Z eff =4+ Z eff =5+ Z eff =6+ Z eff =7+ Z eff =8+

Trends in Z eff Within a period, Z eff increases as Z increases across and σ remains constant: σ = 0 Z = 1+ Z = 2+ Z eff =2 σ = 2 Z = 3+ Z = 4+ Z = 5+ Z = 6+ Z = 7+ Z = 8+ Z = 9+ Z = 10+ σ = 10 Z = 11+ Z = 12+ Z = 13+ Z = 14+ Z = 15+ Z = 16+ Z = 17+ Z = 18+ Z eff =1+ Z eff =2+ Z eff =3+ Z eff =4+ Z eff =5+ Z eff =6+ Z eff =7+ Z eff =8+ Within a group, Z eff remains constant as Z and σ both increase as n increases

Trends in Z eff Within a period, Z eff increases as Z increases across and σ remains constant: σ = 0 Z = 1+ Z = 2+ Z eff =2 σ = 2 Z = 3+ Z = 4+ Z = 5+ Z = 6+ Z = 7+ Z = 8+ Z = 9+ Z = 10+ σ = 10 Z = 11+ Z = 12+ Z = 13+ Z = 14+ Z = 15+ Z = 16+ Z = 17+ Z = 18+ Z eff =1+ Z eff =2+ Z eff =3+ Z eff =4+ Z eff =5+ Z eff =6+ Z eff =7+ Z eff =8+ Within a group, Z eff remains constant as Z and σ both increase as n increases Z eff = # Valence Electrons (outermost electrons with greatest n)

Atomic Radius

Atomic Radius Radius is smallest where Z eff is largest, increases to left as Z eff decreases Electron attraction depends on Z eff Stronger attraction pulls electrons closer to nucleus Radius Increases Electron cloud, radius smaller

Atomic Radius Radius is smallest where Z eff is largest, increases to left as Z eff decreases Electron attraction depends on Z eff Stronger attraction pulls electrons closer to nucleus Radius Increases Electron cloud, radius smaller Radius increases as n increases Radius Increases Electrons in higher energy levels more shielded, farther from nucleus Electron orbitals larger, radius larger

Periodic Variation in Radius

Periodic Variation in Radius Atoms exhibit trends in radius from period to period:

Ionic Radius

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

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

Ionic Radius

Ionic Radius Ionic radius increases down group same trend as atomic radius outer electrons more shielded, less attracted to nucleus

Ionic Radius Ionic radius increases down group same trend as atomic radius outer 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 Positive Ions Negative Ions

Isoelectronic Ions

Isoelectronic Ions In isoelectronic series, all ions have same electron configuration

Isoelectronic Ions In isoelectronic series, all ions have same electron configuration [Ne] [Ar] [Xe]

Isoelectronic Ions In isoelectronic series, all ions have same electron configuration radius decreases as Z (hence Z eff ) increases Stronger electrostatic attraction with same number of electrons [Ne] [Ar] [Xe]