Lewis likes Geometry

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Lewis likes Geometry!

• Who doesnt?!

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• Electron Dot/Lewis Structures are diagrams that
  show valence electrons as dots.

Octet Rule In forming compounds or ions, atoms
try to achieve the electron configuration of a
noble gas. (8 valence e-) (filled outer s and p
levels).
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• Structural formula Shows the arrangement of atoms
  in a molecule each dash represents a pair of
  shared electrons b/n two atoms.
• Unshared pairs of electrons are electrons not
  involved in bonding. (AKA lone pairs)

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Drawing Lewis/Structural Formulas of molecules

• Guidelines
• The total number of e- in a molecule has to be
  the same as the added total of valence electrons
  of all atoms involved.
• i.e. NH3 has 5 3(1) 8 electrons to use.
• Typically, the least electronegative atom is in
  the center of a molecule.
• 3) Hydrogen will ALWAYS be on the outside of the
  atom and will NOT obey octet rule.
• 4) Atoms will form single, double, and/or triple
  bonds in order to have 8 valence electrons (full
  octet)

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• Draw Lewis structure of NH3.

Draw the Structural Formula
Try Drawing the structural formula of the
following molecules F2 H2O SCl2 AsF3 SiH4

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Lewis Structure
Structural Formula
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Now we need to figure out the geometry of the
molecules

• VSEPR Valence Shell Electron Pair Repulsion
  Theory
• The repulsion between electron pairs causes
  molecular shapes to adjust so that the valence
  electron pairs stay as far apart as possible.

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Polarity!
Compounds
Molecular/ Covalent
Ionic
Polar
Nonpolar
Ionic Electronegativity difference of 1.7 or
higher
Polar Covalent Electronegativity difference of
.5 lt x lt 1.7
Nonpolar Covalent Electronegativity difference
of .4 gt x
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Covalent bonds electrons are shared
The electron pairs shared between two atoms are
not necessarily shared equally!

• Bond polarity describes the sharing of electrons
• A nonpolar covalent bond is one in which the
  electrons are shared equally between two atoms
• A polar covalent bond is one in which one atom
  has a greater attraction for the electrons than
  the other atom. If this relative attraction is
  great enough, then the bond is an ionic bond

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Polar Covalent
H2O the O H bond is a polar bond (1.4
electronegativity difference)
d - partial Negative charge
d partial positive charge
Water is a Polar Molecule!
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Pictures taken from

• http//library.thinkquest.org/10429/low/geometry/g
  eometry.htm

http//www.elmhurst.edu/chm/vchembook/images/207e
ptetra.jpg