POLARITY AND SOLUBILITY: “Like dissolves like”

1.a) Review of shapes: What are the five basic shapes?  Linear  Trigonal Planar  Tetrahedral  Trigonal Pyramidal  Bent

1.b) Review of Bonding: Ionic or covalent?  Ionic = metal + nonmetal  Covalent = nonmetal + nonmetal  Nonpolar Covalent = electrons shared equally  Polar Covalent = electrons shared unequally

2. Definitions of Polarity  a)Polar bond— bond involves unequal distribution of electrons  b)Polar molecule— the molecule has an unequal distribution of electrons the molecule has an unequal distribution of electrons  c)Dipole—charges in a molecule are separated; use and

3. To determine if a molecule is polar you must know its shape!  Draw Lewis Structure & Bar Diagram; Use and to show charge distribution  Determine Shape of Molecule  Determine Polarity of Molecule

a) H 2 O  1) Lewis & Bar?  2) Shape?  3) Polarity? O H H O—H H bent Polar—electrons distributed unequally

b) OF 2  1) Lewis & Bar?  2) Shape?  3) Polarity? O—F bent Nonpolar—electrons distributed equally O F F F

b) CF 4  1) Lewis & Bar?  2) Shape?  3) Polarity? tetrahedral Nonpolar—electrons distributed equally F C F F F F—C—F F F

4. Determining solubility: “Like Dissolves Like”  Polar compounds like water dissolve polar and ionic solids like NaCl  Nonpolar compounds like oils and fats dissolve other nonpolar compounds

5. Like Dissolves Like: Why is this important?  Many pesticides and other dangerous toxins are nonpolar and therefore fat soluble  These nonpolar substances build up in the fat reserves of animals, causing harm  DDT in eagles; PCB’s in humans

Determining Solubility Examples: 6. a) Are these pairs soluble?  HCl H 2 O  Both are polar, therefore they are soluble O—H H H—Cl

Determining Solubility Examples: 6. b) Are these pairs soluble?  CF 4 NH 3  CF 4 is nonpolar, NH 3 is polar; therefore NOT SOLUBLE F—C—F F F H—N—H H

7. Practical Application: Chromatography  Pens can be identified using chromatography  Pen ink is a mixture which can be separated using various solvents  A chromatogram (“color picture”) results from the process of chromatography