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1
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- Lewis acid = a substance that accepts an electron pair
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2
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- New bond formed using electron pair from the Lewis base.
- Coordinate covalent bond
- Notice geometry change on reaction.
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3
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- Formation of hydronium ion is also an excellent example.
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4
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5
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- Other good examples involve metal ions.
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6
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- The combination of metal ions (Lewis acids) with Lewis bases such as H2O
and NH3
- ------> COMPLEX IONS
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7
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8
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- [Ni(H2O)6]2+ +
6 NH3 --->
[Ni(NH3)6]2+
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9
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- The heme group in hemoglobin can interact with O2 and CO.
- The Fe ion in hemoglobin is a Lewis acid
- O2 and CO can act as Lewis bases
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10
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- Many complex ions containing water undergo HYDROLYSIS to give acidic
solutions.
- [Cu(H2O)4]2+ + H2O
---> [Cu(H2O)3(OH)]+
+ H3O+
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11
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- This explains why water solutions of Fe3+, Al3+,
Cu2+, Pb2+, etc. are acidic.
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12
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13
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- This explains AMPHOTERIC nature 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.
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14
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- Formation of complex ions explains why you can dissolve a ppt. by
forming a complex ion.
- AgCl(s) e Ag+ +
Cl- Ksp = 1.8 x 10-10
- Ag+ + 2 NH3 --> Ag(NH3)2+ Kform = 1.6 x 107
- -------------------------------------
- AgCl(s) + 2 NH3 e Ag(NH3)2+ + Cl-
- Knet =
__________________
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15
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- Why are some compounds acids?
- Why are some compounds bases?
- Why do acids and bases vary in strength?
- Can we predict variations in acidity or basicity?
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16
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- 1. The electro-negativity of the
O atoms causes the H attached to O to be highly positive.
- 2. The O—H bond is highly polar.
- 3. The H atom of O—H is readily attracted to polar H2O.
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17
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- Trichloroacetic acid is much stronger acid owing to the high
electronegativity of Cl, which withdraws electrons from the rest of the
molecule. This makes the O—H bond highly polar. The H of O—H is very
positive.
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18
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- 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.
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Notes
