lewis acid = electron pair acceptor (bf 3 )lewis acid = electron pair acceptor (bf 3 ) lewis acids...

• Lewis acid = Lewis acid = electron pair electron pair acceptor (BFacceptor (BF33))

Lewis Acids & BasesLewis Acids & BasesLewis Acids & BasesLewis Acids & Bases

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Copyright (c) 1999 by Harcourt Brace & CompanyAll rights reserved

• Lewis acid = electron Lewis acid = electron pair acceptor (BFpair acceptor (BF33))

• Lewis base = Lewis base = electron pair donor electron pair donor (NH(NH33))


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A Lewis acid and base can interact by A Lewis acid and base can interact by sharing an electron pair.sharing an electron pair.


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A Lewis acid and base can interact by A Lewis acid and base can interact by sharing an electron pair.sharing an electron pair.

Formation of Formation of hydronium ion hydronium ion is an excellent is an excellent example.example.

Lewis Acids & BasesLewis Acids & Bases

HH

H

BASEACID

O—H••••

••O—H

H+H

H

H

BASEACID

O—H••••

••O—H

H+++

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Other good examples involve metal ions.Other good examples involve metal ions.

HH

Co2+ ••

BASEACID

O—H••••

••O—H

Co2+


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Other good examples involve metal ions.Other good examples involve metal ions.

Such bonds as the HSuch bonds as the H22O ---> Co bond are often O ---> Co bond are often called called COORDINATE COVALENT COORDINATE COVALENT BONDSBONDS because both electrons are supplied because both electrons are supplied by one of the atoms of the bond.by one of the atoms of the bond.

HH

Co2+ ••

BASEACID

O—H••••

••O—H

Co2+

HH

Co2+ ••

BASEACID

O—H••••

••O—H

Co2+


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The combination of metal The combination of metal ions (Lewis acids) with ions (Lewis acids) with Lewis bases such as Lewis bases such as HH22O and NHO and NH33 ------> ------>

COMPLEX IONSCOMPLEX IONS

All metal ions form All metal ions form complex ions with water complex ions with water —and are of the type —and are of the type [M(H[M(H22O)O)xx]]n+n+ where x = 4 where x = 4

and 6.and 6.


[Cu(NH[Cu(NH33))44]]2+2+

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Add NHAdd NH33 to light blue [Cu(H to light blue [Cu(H22O)O)44]]2+2+ ------> ------>

light blue Cu(OH)light blue Cu(OH)22 and then deep blue and then deep blue

[Cu(NH[Cu(NH33))44]]2+2+


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[Ni(H[Ni(H22O)O)66]]2+2+ + 6 NH + 6 NH33 ---> [Ni(NH ---> [Ni(NH33))66]]2+2+

+ DMG+ DMG


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The Fe2+ in heme can interact with O2 or CO in a Lewis acid-base reaction.


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Many complex ions containing water Many complex ions containing water undergo undergo HYDROLYSISHYDROLYSIS to give acidic to give acidic solutions. solutions.


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Many complex ions containing water undergo Many complex ions containing water undergo HYDROLYSISHYDROLYSIS to give acidic solutions. to give acidic solutions.

[Cu(H[Cu(H22O)O)44]]2+2+ + H + H22O ---> [Cu(HO ---> [Cu(H22O)O)33(OH)](OH)]++ + H + H33OO++


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Many complex ions containing water Many complex ions containing water undergo undergo HYDROLYSISHYDROLYSIS to give acidic to give acidic solutions. solutions.

This explains why water solutions of FeThis explains why water solutions of Fe3+3+, , AlAl3+3+, Cu, Cu2+2+, Pb, Pb2+2+, etc. are acidic., etc. are acidic.


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This explains This explains AMPHOTERICAMPHOTERIC nature of nature of

some metal hydroxides.some metal hydroxides.

Al(OH)Al(OH)33(s) + 3 H(s) + 3 H++ --> Al --> Al3+3+ + 3 H + 3 H22OO

Here Al(OH)Here Al(OH)33 is a Brønsted base. is a Brønsted base.

Al(OH)Al(OH)33(s) + OH(s) + OH-- --> Al(OH) --> Al(OH)44--

Here Al(OH)Here Al(OH)33 is a Lewis acid. is a Lewis acid.


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This explains This explains AMPHOTERICAMPHOTERIC nature of nature of

some metal hydroxides.some metal hydroxides.

Al(OH)Al(OH)33(s) + 3 H(s) + 3 H++ --> Al --> Al3+3+ + 3 H + 3 H22OO

Here Al(OH)Here Al(OH)33 is a Brønsted base. is a Brønsted base.

Al(OH)Al(OH)33(s) + OH(s) + OH-- --> Al(OH) --> Al(OH)44--

Here Al(OH)Here Al(OH)33 is a Lewis acid. is a Lewis acid.

Al3+ O—H-••••••

Al3+ O—H-••••

••


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Amphoterism of Al(OH)Amphoterism of Al(OH)33

Al(OH)Al(OH)33 on right on right Add NaOHAdd NaOH Add HClAdd HCl

See Kotz/Treichel, page 830See Kotz/Treichel, page 830

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Neutral Lewis AcidNeutral Lewis AcidNeutral Lewis AcidNeutral Lewis AcidCarbon dioxide is a neutral Lewis acid.Carbon dioxide is a neutral Lewis acid.

+1.5+1.5 -0.75-0.75-0.75-0.75

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Many complex ions are very Many complex ions are very stable.stable.

CuCu2+2+ + 4 NH + 4 NH33 [Cu(NH[Cu(NH33))44]]2+2+

K for the reaction is called K for the reaction is called

KKformationformation

or a “formation constant”or a “formation constant”

Here K = 6.8 x 10Here K = 6.8 x 101212. Reaction is . Reaction is strongly product-favored.strongly product-favored.


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Formation of complex ions explains why you Formation of complex ions explains why you can dissolve a ppt. by forming a complex can dissolve a ppt. by forming a complex ion. ion.

AgCl(s) + 2 NHAgCl(s) + 2 NH33

Ag(NHAg(NH33))22+ + + Cl+ Cl--


AgCl(s)

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Formation of complex ions explains why you Formation of complex ions explains why you can dissolve a ppt. by forming a complex ion. can dissolve a ppt. by forming a complex ion.

AgCl(s) AgCl(s) AgAg++ + Cl + Cl-- K Kspsp = 1.8 x 10 = 1.8 x 10-10-10

AgAg++ + 2 NH + 2 NH33 --> Ag(NH --> Ag(NH33))22++ K Kformform = 1.6 x 10 = 1.6 x 1077

--------------------------------------------------------------------------

AgCl(s) + 2 NHAgCl(s) + 2 NH33 Ag(NHAg(NH33))22+ + + Cl+ Cl--

KKnetnet = K = Kspsp • K • Kformform = 2.9 x 10 = 2.9 x 10-3-3


lewis acid = electron pair acceptor (bf 3 )lewis acid = electron pair acceptor (bf 3 ) lewis acids...

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