Shielding & Atomic Radius, Ions & Ionic Radius. Chemistry AP

Transcription

1 Shielding & Atomic Radius, Ions & Ionic Radius Chemistry AP

2 Periodic Table

3 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

4 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 e : [Ne]3s 2 3p 1 [Ne]

5 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 e : [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]

6

7 Special Ion Formation Transition metals lose ns 2 electrons before (n 1)d x : Fe Fe e : [Ar]4s 2 3d 6 [Ar]3d 5 Ni Ni e : [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

8 Special Ion Formation Transition metals lose ns 2 electrons before (n 1)d x : Fe Fe e : [Ar]4s 2 3d 6 [Ar]3d 5 Ni Ni e : [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 e : [Kr]5s 2 4d 10 5p 2 [Kr]5s 2 4d 10 Sn Sn e : [Kr]5s 2 4d 10 5p 2 [Kr]4d 10 Full (n 1)d 10 called pseudo-noble gas configuration

9 Effective Nuclear Charge

10 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

11 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

12 Trends in Zeff

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

14 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+

15 Trends in Z eff Within a period, Z eff increases as Z increases across and σ remains constant: σ = 0 Z = 1+ Z = 2+ Zeff=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+ Zeff=1+ Zeff=2+ Zeff=3+ Zeff=4+ Zeff=5+ Zeff=6+ Zeff=7+ Zeff=8+

16 Trends in Z eff Within a period, Z eff increases as Z increases across and σ remains constant: σ = 0 Z = 1+ Z = 2+ Zeff=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+ Zeff=1+ Zeff=2+ Zeff=3+ Zeff=4+ Zeff=5+ Zeff=6+ Zeff=7+ Zeff=8+ Within a group, Z eff remains constant as Z and σ both increase as n increases

17 Trends in Z eff Within a period, Z eff increases as Z increases across and σ remains constant: σ = 0 Z = 1+ Z = 2+ Zeff=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+ Zeff=1+ Zeff=2+ Zeff=3+ Zeff=4+ Zeff=5+ Zeff=6+ Zeff=7+ Zeff=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)

18 Atomic Radius

19 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 Electron cloud, radius smaller Radius Increases

20 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 Electron cloud, radius smaller Radius increases as n increases Electrons in higher energy levels more shielded, farther from nucleus Electron orbitals larger, radius larger Radius Increases Radius Increases

21 Periodic Variation in Radius

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

23 Ionic Radius

24 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

25 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

26 Ionic Radius

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

28 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

29 Isoelectronic Ions

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

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

32 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]