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May 11, 2016
CHEM 121
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• The steric number determines the electronic shape (EG), TRIGONAL PLANAR
• The atoms determine the molecular shape (MG), TRIGONAL PLANAR & BEN

• Note: electron pairs are not “bonded” to the central atom, cannot be seen, so shape is
determined by the atoms
• 3 types of repulsions:
Lone pair-lone pair > lone pair-bonded pair > bond pair-bond pair
• Lone pairs occupy more space, cause increased repulsions
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• MINIMIZE REPULSIONS by MAXIMIZING SPACE around central atom

Different Shapes of Electronic Geometry

Linear

Tetrahedral

Trigonal
Planar

Trigonal
Bipyramidal

Octahedral (8
faces)

Molecular geometry: based off the electronic geometry

Polarity: NaCl is ionic so
you see a complete
transfer of electrons
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HCL is polar
covalent and Cl2 is non
polar covalent
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O=C=O (incomplete Lewis structure)
(trig planar)

BCl BCl F

(tetrahedral)

CH , CH Cl, CH Cl

3,

4

2

3

2

2

This shows that to be nonpolar, they cancel each other out by all being the same length
But for polar molecules, they do not cancel because of the unequal bonds
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Isomers- plane of symmetry
• These show two isomers that can be drawn by their lines of symmetry
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The trans (meaning opposite) is symmetrical
in the opposite way, but folding the sketch vertically

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