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Molecular Shapes and Polarity

Molecular Shapes and Polarity. VSEPR Theory. Definition: the repulsion between electron pairs causing shapes to adjust so that the valence electrons pairs stay as far away as possible Shapes of Molecules (see chart inside chem helper) Linear Bent Trigonal Planar Trigonal Pyramidal

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Molecular Shapes and Polarity

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  1. Molecular Shapes and Polarity

  2. VSEPR Theory • Definition: the repulsion between electron pairs causing shapes to adjust so that the valence electrons pairs stay as far away as possible • Shapes of Molecules (see chart inside chem helper) • Linear • Bent • Trigonal Planar • Trigonal Pyramidal • Tetrahedal

  3. Determining Bond Polarity • Electronegativity: ability to attract electrons • As electronegativity increases, the more strongly it attracts electrons • Look at the difference in electronegativity values to determine bond polarity • If the electronegativity is the same, it is an even sharing of electrons; the bond is non-polar • If there is a difference in electronegativity, the atom with the greater electronegativity will pull the pair of electrons closer. Example: HCl Cl=3.0 H =2.1 .9 = polar

  4. Determining Molecular Polarity • The presence of a polar bond in a molecule may make the entire molecule polar • In polar molecules, one end of the molecule is δ (-) and one end is δ (+) • Example: H2O • Effect of polar bonds on molecular polarity depends on the molecular shape and orientation of the polar bonds.

  5. Example of Molecular Polarity • Water • Chlorine • Carbon Dioxide

  6. Attractions between Molecules – Intermolecular Attractions Intermolecular Forces: IMFs The attraction between MOLECULES Relative Strength: weaker than the ionic or covalent bonds within the molecule

  7. VanderWaals Forces • Dipole Interactions: • When polar molecules are attracted • Attraction between opposite charges • Dispersion Forces: • Weakest • Occur even between non-polar molecules

  8. Hydrogen Bonds • Strongest of the IMFs • H is bonded to a highly electronegative atom • F, O, N

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