Lewis Acids & Bases. Lewis acid = a substance that accepts an electron pair. Lewis base = a substance that donates an electron pair. Reaction of a Lewis Acid and Lewis Base. New bond formed using electron pair from the Lewis base. Coordinate covalent bond Notice geometry change on reaction.
Lewis acid = a substance that accepts an electron pair
Lewis base = a substance that donates an electron pair
Formation of hydronium ion is also an excellent example.
Other good examples involve metal ions.
The combination of metal ions (Lewis acids) with Lewis bases such as H2O and NH3
------> COMPLEX IONS
[Ni(H2O)6]2+ + 6 NH3 ---> [Ni(NH3)6]2+
See page 924
Many complex ions containing water undergo HYDROLYSIS to give acidic solutions.
[Cu(H2O)4]2+ + H2O ---> [Cu(H2O)3(OH)]+ + H3O+
This explains why water solutions of Fe3+, Al3+, Cu2+, Pb2+, etc. are acidic.
This interaction weakens this bond
Another H2O pulls this H away as H+
This explains AMPHOTERICnature of some metal hydroxides.
Al(OH)3(s) + 3 H+ --> Al3+ + 3 H2O
Here Al(OH)3 is a Brønsted base.
Al(OH)3(s) + OH- --> Al(OH)4-
Here Al(OH)3 is a Lewis acid.
Formation of complex ions explains why you can dissolve a ppt. by forming a complex ion.
AgCl(s) eAg+ + Cl- Ksp = 1.8 x 10-10
Ag+ + 2 NH3 --> Ag(NH3)2+ Kform = 1.6 x 107
AgCl(s) + 2 NH3eAg(NH3)2+ + Cl-
Knet = __________________
Ka = 1.8 x 10-5
Ka = 0.3
These ions are BASES.
They become more and more basic as the negative charge increases.
As the charge goes up, they interact more strongly with polar water molecules.