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MOLECULAR POLARITY

MOLECULAR POLARITY. Ch 8. BOND VS. MOLECULAR POLARITY. Covalent Bonds: Dogs of equal strength.

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MOLECULAR POLARITY

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  1. MOLECULAR POLARITY Ch 8

  2. BOND VS.MOLECULAR POLARITY

  3. Covalent Bonds: Dogs of equal strength. Covalent bonds can be thought of as two or more dogs with equal attraction to the bones.  Since the dogs (atoms) are identical (same electronegativities, then the dogs share the pairs of available bones evenly.  Since one dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs.  The molecule is not "polar" meaning one side does not have more charge than the other.

  4. Electronegativity The ability of an atom to attract electrons when the atom is in a compound. See Table for Individual Element Values

  5. Polar Covalent Bonds: Unevenly matched but willing to share. These bonds can be thought of as two or more dogs that have different desire for bones (different electronegativities).  The bigger dog has more strength to possess a larger portion of the bones.  Sharing still takes place but is an uneven sharing.  In the case of the atoms, the electrons spend more time on the end of the molecule near the atom with the greater electronegativity (desire for the electron) making it seem more negative and the other end of the molecule seem more positive.

  6. BOND POLARITY 1. Identical non-metallic atoms have the same electronegativities and form non-polar bonds. -electrons are shared equally between the two atoms EX: F2 = nonpolar covalent bond 2. When two non-metallic atoms have different electronegativities (< 1.67) they form polar covalent bonds. -electrons are shared unequally between the two atoms EX: O-H= polar covalent bond

  7. BOND POLARITY

  8. To determine polarity First – identify if bond is ionic or covalent Second- if there is a metal and nonmetal it is IONIC (even if subtraction says otherwise) if its COVALENT (non metals) - determine if bond is nonpolar or polar covalent (even if subtraction says otherwise) NOTE: REMEMBER TO TAKE ABSOLUTE VALUE

  9. CALCULATIONS: • F2 F – F • | 4.0 – 4.0| = 0 Nonpolar Covalent (NPC) • CO2 C – O • | 2.51 – 3.5| = 0.99 Polar Covalent (PC) • NaCl Na – Cl • | 0.9 – 3.0| = 2.1 Ionic

  10. DRAWINGS: • Delta (-) Indicates the more electronegative • Delta (+) Indicates the lower electronegative atom • O= 2.5 H = 2.1

  11. POLAR MOLECULES 1. Must have at least one polar bond 2. One end of molecule is (+) & the other end is (-) 3. Polar molecules are also known as dipoles 4. Uneven distribution of electrons in the molecule Nonpolar covalentpolar covalent

  12. 2 Things Determine Whether a Molecule is Polar: 1. Polarity of a Molecule’s Bonds - Electronegativity differences of atoms - Use Table to determine if a bond is Nonpolar covalent, Polar covalent, or Ionic  2. Shape of a Molecule (Molecule Polarity) - If molecule is made of more than two atoms, the shape of the molecule determines the polarity

  13. So, if bond is polar….. Then look at the molecules shape. EX: H2O O-H polar covalent bond Look at shape of water Bent, so molecule is also polar

  14. BUT….. Sometimes you have polar bonds and a nonpolar molecule.

  15. If polar bonds are distributed evenly throughout the molecule, then the molecule is: NONPOLAR COVALENT EX: CCl4 -C-Cl bond is Polar covalent, but overall molecule is Nonpolar due to the shape of the molecule. -Symmetrical Distribution cancels out the effects of bond polarity. POLAR BONDS BUT NONPOLAR MOLECULE

  16. 2.1 2.51 2.1 2.1 2.1 Polar bonds= 2.51-2.1=.41 Nonpolar molecule= Due to the symmetrical shape of the molecule ONLY SYMMETRICAL MOLECULES CANCEL OUT BOND POLARITY

  17. ONLY SYMMETRICAL MOLECULES CANCEL BOND POLARITY

  18. MOLECULAR POLARITY

  19. Intermolecular Forces 1. Attraction between MOLECULES 2. These forces are weaker than either ionic or covalent bonds. TYPES: A. Van der Waals Forces 1. Dipole interactions 2. Dispersion Forces B. Hydrogen Bonds

  20. Van der Waals Forces the two weakest attractions between molecules 1. Dipole Interactions: -Occur when polar molecules are attracted to one another Ex: H2O is attracted to another H2O 2. Dispersion Forces: -The weakest of all intermolecular interactions -Occurs between nonpolar molecules -Caused by the motion of e-s Ex: F2, Cl2 (gases), Br2 (liquid), I2 (solid)

  21. Dipole Interaction - +

  22. Br Br δ- δ+ More e- Br Br δ- δ+ More e- Dispersion Forces

  23. Hydrogen Bonds 1. When a hydrogen atom that is bonded to a very electronegative atom is attracted to an unshared pair of another electronegative atom. 2. When H is bonded directly to an O,N,F 3. Strongest of Intermolecular Forces

  24. Hydrogen Bonding

  25. CHAPTER 15 SECTION 1:WATER AND ITS PROPERTIES

  26. Water and Its Properties • High surface tension and low vapor pressure result from hydrogen bonding. • Solid water has a lower density than liquid water. Review article on Removing Stains

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