1. Lewis acid = electron pair acceptor (BF 3 )Lewis acid = electron pair acceptor (BF 3 ) Lewis Acids & Bases Copyright © 1999 by Harcourt Brace & Company All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida

2. 2 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Lewis acid = electron pair acceptor (BF 3 )Lewis acid = electron pair acceptor (BF 3 ) Lewis base = electron pair donor (NH 3 )Lewis base = electron pair donor (NH 3 ) Lewis Acids & Bases

3. 3 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved A Lewis acid and base can interact by sharing an electron pair. Lewis Acids & Bases

4. 4 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved A Lewis acid and base can interact by sharing an electron pair. Formation of hydronium ion is an excellent example. Lewis Acids & Bases +

5. 5 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Other good examples involve metal ions. Lewis Acids & Bases

6. 6 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Other good examples involve metal ions. Such bonds as the H 2 O ---> Co bond are often called COORDINATE COVALENT BONDS because both electrons are supplied by one of the atoms of the bond. Lewis Acids & Bases

7. 7 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved The combination of metal ions (Lewis acids) with Lewis bases such as H 2 O and NH 3 ------> COMPLEX IONS All metal ions form complex ions with water —and are of the type [M(H 2 O) x ] n+ where x = 4 and 6. Lewis Acids & Bases [Cu(NH 3 ) 4 ] 2+ [Cu(NH 3 ) 4 ] 2+

8. 8 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Add NH 3 to light blue [Cu(H 2 O) 4 ] 2+ ------> light blue Cu(OH) 2 and then deep blue [Cu(NH 3 ) 4 ] 2+ Lewis Acids & Bases

9. 9 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved [Ni(H 2 O) 6 ] 2+ + 6 NH 3 ---> [Ni(NH 3 ) 6 ] 2+ [Ni(H 2 O) 6 ] 2+ + 6 NH 3 ---> [Ni(NH 3 ) 6 ] 2+ + DMG Lewis Acids & Bases

10. 10 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved The Fe 2+ in heme can interact with O 2 or CO in a Lewis acid-base reaction. Lewis Acids & Bases

11. 11 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Many complex ions containing water undergo HYDROLYSIS to give acidic solutions. Lewis Acids & Bases

12. 12 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Many complex ions containing water undergo HYDROLYSIS to give acidic solutions. [Cu(H 2 O) 4 ] 2+ + H 2 O ---> [Cu(H 2 O) 3 (OH)] + + H 3 O + Lewis Acids & Bases

13. 13 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Many complex ions containing water undergo HYDROLYSIS to give acidic solutions. This explains why water solutions of Fe 3+, Al 3+, Cu 2+, Pb 2+, etc. are acidic. Lewis Acids & Bases

14. 14 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved This explains AMPHOTERIC nature of some metal hydroxides. Al(OH) 3 (s) + 3 H + --> Al 3+ + 3 H 2 O Here Al(OH) 3 is a Brønsted base. Al(OH) 3 (s) + OH - --> Al(OH) 4 - Here Al(OH) 3 is a Lewis acid. Lewis Acids & Bases

15. 15 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved This explains AMPHOTERIC nature of some metal hydroxides. Al(OH) 3 (s) + 3 H + --> Al 3+ + 3 H 2 O Here Al(OH) 3 is a Brønsted base. Al(OH) 3 (s) + OH - --> Al(OH) 4 - Here Al(OH) 3 is a Lewis acid. Lewis Acids & Bases

16. 16 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Amphoterism of Al(OH) 3 Al(OH) 3 on right Add NaOH Add HCl See Kotz/Treichel, page 830

17. 17 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Neutral Lewis Acid Carbon dioxide is a neutral Lewis acid. +1.5-0.75-0.75

18. 18 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Many complex ions are very stable. Cu 2+ + 4 NH 3 [Cu(NH 3 ) 4 ] 2+ K for the reaction is called K formation or a “formation constant” Here K = 6.8 x 10 12. Reaction is strongly product-favored. Lewis Acids & Bases

19. 19 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Formation of complex ions explains why you can dissolve a ppt. by forming a complex ion. AgCl(s) + 2 NH 3 Ag(NH 3 ) 2 + + Cl - Ag(NH 3 ) 2 + + Cl - Lewis Acids & Bases AgCl(s)

20. 20 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Formation of complex ions explains why you can dissolve a ppt. by forming a complex ion. AgCl(s) Ag + + Cl - K sp = 1.8 x 10 -10 Ag + + 2 NH 3 --> Ag(NH 3 ) 2 + K form = 1.6 x 10 7 ------------------------------------- AgCl(s) + 2 NH 3 Ag(NH 3 ) 2 + + Cl - K net = K sp K form = 2.9 x 10 -3 K net = K sp K form = 2.9 x 10 -3 Lewis Acids & Bases