Polarity – It exists in two forms Bond Polarity We looking at the difference in electronegativies between atoms to determine how they share their electrons.

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Presentation transcript:

Polarity – It exists in two forms Bond Polarity We looking at the difference in electronegativies between atoms to determine how they share their electrons. Evenly or Unevenly Molecule Polarity We are looking at all the atoms surrounding the center atom and determine if there is symmetry or not. Symmetrical or Asymmetrical

Bond Polarity  The difference in electronegativities affects how atoms bond together.  Using the electronegativity values, we can predict the type of bond that forms.  Although all covalent bonds involve the sharing of electrons, most of the time this sharing is not equal.

 If one atom has a higher electronegativity than the other atom, it “hogs” the shared bonded pair of electrons most of the time.  This type of covalent bond is known as a polar covalent bond.  Polar bonds mean NOT EVEN! SF

Electronegativity Difference If the difference in electronegativities is between: – 1.8 to 4.0: Ionic A big difference, so an element pulls an electron off another. – 0.4 to 1.7: Polar Covalent A moderate difference, so they have to share, but not evenly. – 0.0 to 0.3: Non-Polar Covalent A small difference, so they share, and share evenly. Example: NaCl Na = 0.8, Cl = 3.0 Difference is 2.2, so this is an ionic bond!

Bond Polarity HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity) HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity) Cl has a greater share in bonding electrons than does H. We draw a dipole moment showing how the shared electrons are being pulled. Cl has slight negative charge (-  ) H has slight positive charge (+  )

Bond Polarity “Like Dissolves Like” “Like Dissolves Like” – Polar dissolves Polar – Nonpolar dissolves Nonpolar

Polarity of Whole Molecule  Determining the polarity of a bond is easy, but what about the molecule as a whole?  Strangely enough, you can have nonpolar molecules that contain polar bonds!  SO….  How do you determine if a molecule itself is going to be polar or nonpolar?  Look at the Lewis Structure and check out the central atom!

Determining if a Molecule is Nonpolar or Polar Look at what is attached to the central atom If every attached structure is the same The molecule is perfectly symmetrical And therefore NONPOLAR If the attached structures are different The molecule is asymmetrical And therefore POLAR

H δ+δ+δ+δ+ δ -δ -δ -δ - Polar Bond Br Asymetrical Polar Molecule

OCO== δ +δ +δ +δ + δ +δ +δ +δ + δ -δ -δ -δ - δ -δ -δ -δ - Polar Bonds However, the shape is symmetrical So… The molecule is nonpolar

Br Br Nonpolar Bond Symmetrical Nonpolar Molecule