17'8: Colloids

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17.8 Colloids

• Solution Homogeneous mixture
• Colloid Heterogeneous mixture
• Distinct particles suspended in some medium

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The Tyndall effect

• Collids have 1 1000 nm aggregates dispersed in
  solution
• These aggregates scatter light
• A solution has no light scattering
• No aggregates!

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What stabilizes a colloid?

• Particles attract a layer of ions of the same
  charge
• This electrostatic repulsion helps stabilize
  colloid

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Chapter 19

• Transition Metals and Coordination Chemistry
• (Chapter 20 in 5th edition of book)

Solid K3Fe(CN)6
Metal EDTA Complex
Aqueous Co(NH3)5ClCl2
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Transition Metals

• Useful for many things as neutral solids
• Building Materials (iron, copper, titanium,
  steel)
• Electrical conductivity (wires made of copper)
• In chemistry, metal ions form compounds with
  nonmetals, called either
• Complex ions
• Coordination complex
• Coordination compound

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Electron Configurations

• Electron Configurations are different between
  metals and metal ions
• Metals as you would expect

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Electron Configurations

• Except
• Cr Ar 4s 1 3d 5
• Cu Ar 4s 1 3d 10
• Special Stability of filled or half-filled d
  orbitals

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Metals vs. Metal Ions

• Cobalt Metal (Co0)

Cobalt Ion (Co2)
3dxz dyz dxy dz2 dx2-y2
4s
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Metal Ions

• Transition metal ions do not have s electrons
• Example Electron configuration of vanadium

Ar 4s2 3d3
Ar 3d4
Ar 3d2
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Coordination Compounds
Almost all metal ions found as complexes
Complex Ion
Ligand
Metal Ion (Co3)
Counter Ion, for charge balance
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Coordination Compounds

• Metal-Ligand bond is mostly covalent
• Complex ion Counter ion bond is purely ionic

Dissociates in Solution
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Coordination Number

• Number of bonds from metal ion to ligands
• Difficult to predict either 2, 4 or 6

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Coordination Number

• What is the coordination number of the cobalt in
• Co(NH3)5ClCl2 
• Co(NH3)5Cl 2
• Co(H2O)42

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Ligands

• Ligand a lewis base that binds to a metal ion
• Remember
• Lewis Acid electron-pair acceptor
• Lewis Base electron-pair donor (has lone pair)
• Ligand binding results in a coordinate covalent
  bond

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Some Common Ligands

• Monodentate (one bond to metal ion)

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Examples

• V(NH3)6Cl3
• Mn(H2O)4(Cl)2SO4

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Some Common Ligands

• Bidentate Ligands (two bonds to metal ion)
• Any ligand with more than one bond called a
  chelating ligand

Example Fe(en)2(NH2)2Br2
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Some Common Ligands

• Polydentate Ligands
• Tridentate
• Tetradentate
• EDTA (ethylene diamine tetra acetate)