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Dipoles and Polar Molecules
Page 80 Link to Phet Polar Molecules
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Dipole An uneven distribution of electron density a molecule.
Results in a partial + and partial - . Direction of dipole shown by arrow pointing toward negative end (cross on arrow near + end)
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Polar Molecules Step 1: Lewis Dot (water)
Molecules with a “net” or total dipole. Three steps in determining polarity: Step 1: Lewis Dot (water)
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Step 2: Geometry 2 2 Bonding Regions? Nonbonding Pairs?
Geometry is Bent or Angular 2 2 Link to VSEPR
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Step 3: Examine arrangement of charges
Check for Symmetry of Charges Step 3: Examine arrangement of charges 1) Polar Bonds : EN difference between atoms
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If NO POLAR BONDS MOLECULE IS ALWAYS NONPOLAR
O2 NONPOLAR EN O = 3.5; ∆EN = = 0
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2) Nonbonding (lone) Pairs on Central Atom
Regions of - charge ONLY IMPORTANT IF OUTSIDE ATOMS ARE H
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3) Symmetry of Polar Bonds within Molecule:
If symmetric = NONPOLAR NO NET DIPOLE Carbon Dioxide POLAR BONDS CANCEL; EQUAL AND OPPOSITE
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Roping Analogy Equal and Opposite Forces
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Concept of equal and opposite forces
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3) Symmetry of Polar Bonds within Molecule: NOT symmetric = POLAR
(overall or Net dipole)
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If molecular geometry is not correct – symmetry may be misjudged
CORRECT! WATER IS BENT AND POLAR!! WRONG! Water is NOT LINEAR and NONPOLAR
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Water
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All identical outside atoms + NO nonbonding pairs on central atom= symmetric (non-polar)
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Sample Polarities Link to video polarities and shapes
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