Week 4, Section Bonds: Tug of war for electrons

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Week 4, Section Bonds Tug of war for electrons

• 9/30/05

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H2

• H-H
• Do both atoms contribute equally to the bond?

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HCl

• Do both atoms contribute equally to the bond?
• Are the electrons in the bond shared equally by
  both atoms?

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Polarity

• Polarity is an unequal sharing of electrons
• What causes polarity in HCl?

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Electronegativity

• the ability of an atom in a covalent bond to
  attract shared electrons to itself

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Is the molecule polar?

• CO2
• NH3
• SF4

In order to determine polarity, you must
visualize the tug-of-war going on in the molecule
for the electrons.
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For a molecule to be polar it must

• 1. have at least 1 polar bond or 1 lone pair
• 2. and polar bonds or lone pairs must be arranged
  in space so that the dipoles do not cancel out

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Are they polar?

• C2H2
• XeF2
• BF3
• SF6
• CHCl3
• XeF4
• ICl3
• BrF5

Report back Valence electrons Lewis
structure Molecular structure Dipole (if any)
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Polarity of molecules

• Electron density maps (color)
• Plus-arrows

CHCl3
BrF5
SCN-
SO2 or H2O?