Lecture 8.4b- Polar Molecules


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Section 8.4 lecture (part B) for Honors & Prep Chemistry

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Lecture 8.4b- Polar Molecules

  1. 1. BELLWORK- Determine Shape Draw the Lewis Dot Structure and the 3D structure for ethane (C 2 H 6 ) and ethene (C 2 H 4 ). Do these molecules have any polar bonds?
  2. 2. In review Equal sharing of electrons = covalent LOW electronegativity difference Unequal sharing of electrons = polar MEDIUM electronegativity difference Transfer of electrons = ionic HIGH electronegativity difference
  3. 3. 2 bonding domains Three bonding domains Four bonding domains Three bonding and one lone pair Two bonding and two lone pairs
  4. 4. Bond polarity and molecule shape determine if a molecule is polar Bond polarity --- When a bond has a partial negative charge on one atom and a partial positive charge on the other atom. Molecule shape--- the arrangement of atoms in three dimensions (3-D)
  5. 5. A polar molecule has polar bonds and asymmetry
  6. 6. A polar molecule has polar bonds and asymmetry Polar bonds Non-polar molecule Symmetry- all sides are the same δ - δ - δ - δ - δ +
  7. 7. A polar molecule has polar bonds and asymmetry Polar bonds Non-polar molecule Symmetry- all sides are the same Polar bonds Polar molecule Asymmetry- has different sides δ - δ - δ - δ - δ - δ + δ + negative side Positive side
  8. 8. If the electrons are not distributed equally, the molecule is polar. The molecule has a negative end and a positive end.
  9. 9. A polar molecule has a partially positive side and a partially negative side. The arrow labels the molecular polarity. It shows that electrons are mostly by the oxygen atom O H H
  10. 10. Polar molecules are affected by electric fields
  11. 11. Polar molecules have two poles; one is partially positive and one is slightly negative. Positive end Negative end N H H H
  12. 12. The positive pole (  + ) is attracted to negative ions and the negative poles(  - ) in other polar molecules. POLAR MOLECULES INTERACT!!
  13. 13. + POLAR MOLECULES INTERACT!! The negative pole (  - ) is attracted to positive ions and the positive poles(  + ) in other polar molecules.
  14. 14. Water is a molecule that has two polar O-H bonds.
  15. 15. The electrons are not distributed evenly, so the water molecule is polar. The negative pole is at the oxygen. O is more electronegative than H, so electrons are pulled toward O. Also, there are two lone pairs around oxygen. negative end positive end
  16. 16. Na + (aq) A dissolved sodium ion
  17. 17. Water is very good at dissolving salts because it can surround anions & cations.
  18. 18. Practice- Using last night’s homework assignment, label the molecular polarity on the four pictures H F
  19. 19. <ul><li>For the rest of the period work on your molecular modeling lab </li></ul><ul><li>Find a molecule that contains polar bonds </li></ul><ul><li>Build the molecule using a molecular modeling kit </li></ul><ul><li>Draw a sketch of the molecule </li></ul><ul><ul><li>Label the bond polarity using δ + and δ - </li></ul></ul><ul><ul><li>Label the molecular polarity using </li></ul></ul>HW- complete bonding practice problems #1-#17 Tuesday = cover network solids and intermolecular forces. HW- Section 8.4 Block Day = Complete modeling lab, plus finish bonding practice problems. Friday = Chapter Eight QUIZ!!
  20. 20. Practice- Draw the 3D structures for these molecules and label the bond polarity and the molecule polarity. <ul><li>H 2 O </li></ul><ul><li>CH 4 </li></ul><ul><li>CH 3 F </li></ul><ul><li>CH 3 CH 3 </li></ul><ul><li>CH 3 CH 2 OH </li></ul><ul><li>6. NH 3 </li></ul>7. CO 2 8. CH 2 CH 2 9. HCN 10. 11.