Molecular Polarity

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Molecular Polarity

• Covalent Bonding

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Covalent Bonds involve sharing electrons But Just
like in real life, not all sharing Is equal !!!
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/Electronegativity
Electronegativity is the ability of an atom to
Attract electrons to itself in a covalent bond
Large Electronegavity
Small Electronegativity
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So, the atoms in a covalent bond are engaged in a
tug-of-war over electrons
electrons
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• The atom that wins will be the one that is
  more electronegative.
• Because this atom gets the electrons more of the
  time, it becomes slightly negative
• The atom that loses becomes slightly positive

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The Periodic Table allows us To predict
differences in electronegavity
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(No Transcript)
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Results of Tug of War
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A. Dipole Moment

• Means the direction of the polar bond in a
  molecule.
• Arrow points toward the more electronegative
  atom. (The direction the electrons will flow

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B. Determining Molecular Polarity

• Depends on
• dipole moments
• molecular shape

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Linear
Bent
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Linear
Bent
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Trigonal Planar
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Tetrahedral
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B. Determining Molecular Polarity

• Nonpolar Molecules
• Dipole moments are symmetrical and cancel out.

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B. Determining Molecular Polarity

• Polar Molecules
• Dipole moments are asymmetrical and dont cancel .

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B. Determining Molecular Polarity

• Therefore, polar molecules have...
• asymmetrical shape (lone pairs) or
• asymmetrical atoms

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So, polarity is more of a spectrum than a
black and white determination
Polar---------------------------------------------
---------nonpolar
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More Nonpolar Molecules

• Share electrons the best
• Have the closest electronegativities (or smallest
  differences)
• Have lower boiling and melting points
• . . .so More likely to be gases at room
  temperature
• Like dissolves like . . .
• Use a nonpolar solvent to dissolve a nonpolar
  solute

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More Polar Molecules

• Do not share well at all!
• Their electronegativity differences are great
• Are more like ionic compounds
• Have higher melting and boiling points
• Most likely to be liquids at room temperature
• Like dissolves like . . .
• Use a polar/ionic solvent to dissolve a
  polar/ionic solute

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Ionic, Polar, Nonpolar A Continuum Ionic--------
----------------Polar----------------Nonpolar Elec
trons transferred E- shared unequally E-
shared High mp/bp
Low mp/bp Solids at STP
Liquids at STP Gas at STP