Nonpolar Covalent Bonds

1
Nonpolar Covalent Bonds

• If the electrons are shared equally, it is called
  a nonpolar covalent bond. (This type of bond only
  occurs if the electrons are shared between atoms
  having similar electronegativities and results in
  no net charges)

2
Polar Covalent Bonds

• If the electrons are shared unequally, it is
  called a polar covalent bond.
• The unequal sharing results in a partial positive
  charge and a partial negative charge called
  dipoles.
• The atom having the greater electronegativity
  will have the partial negative charge.

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Review
4
Nonpolar Molecules

• Molecules consisting of nonpolar bonds are also
  nonpolar.
• Examples of nonpolar molecules include all of the
  diatomic molecules (H2, N2, O2, Cl2, Br2, I2, F2)

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Molecules Polar or Nonpolar

• Just because a molecule possesses polar bonds
  does not mean the molecule as a whole will be
  polar.
• If the dipoles cancel (the dipoles are arranged
  symmetrically), the molecule is nonpolar.
• If the dipoles do not cancel (the dipoles are
  arranged asymmetrically), the molecule is polar.
• By adding the individual bond dipoles, one can
  determine the overall dipole moment for the
  molecule.

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Review of Polarity
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Like Dissolves Like

• Nonpolar molecules will dissolve in other
  nonpolar substances due to their similar
  structure.
• Polar molecules will dissolve in other polar
  molecules due to the force of attraction between
  the positive end of one polar molecule and
  negative end of another polar molecule.
• Ionic compounds will also dissolve in polar
  compounds.
• Corn oil does not dissolve in water. Is corn oil
  polar or nonpolar?

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Molecular Geometries
Chemistry, The Central Science, 10th
edition Theodore L. Brown, H. Eugene LeMay, Jr.,
and Bruce E. Bursten
? 2006, Prentice-Hall, Inc.
9
Molecular Shapes

• The shape of a molecule plays an important role
  in its reactivity.
• By noting the number of bonding and nonbonding
  electron pairs we can easily predict the shape
  and polarity of the molecule.

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What Determines the Shape of a Molecule?

• Simply put, electron pairs, whether they be
  bonding or nonbonding, repel each other.
• By assuming the electron pairs are placed as far
  as possible from each other, we can predict the
  shape of the molecule.

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Electron Domains

• We can refer to the electron pairs as electron
  domains.
• In a double or triple bond, all electrons shared
  between those two atoms are on the same side of
  the central atom therefore, they count as one
  electron domain.

• This molecule has four electron domains.

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Valence Shell Electron Pair Repulsion Theory
(VSEPR)

• The best arrangement of a given number of
  electron domains is the one that minimizes the
  repulsions among them.

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Electron-Domain Geometries

• These are the electron-domain geometries for two
  through six electron domains around a central
  atom.

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Electron-Domain Geometries

• All one must do is count the number of electron
  domains in the Lewis structure.
• The geometry will be that which corresponds to
  that number of electron domains.

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Molecular Geometries

• The electron-domain geometry is often not the
  shape of the molecule, however.
• The molecular geometry is that defined by the
  positions of only the atoms in the molecules, not
  the nonbonding pairs.

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Molecular Geometries

• Within each electron domain, then, there might
  be more than one molecular geometry.

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Linear Electron Domain

• In this domain, there is only one molecular
  geometry linear.
• NOTE If there are only two atoms in the
  molecule, the molecule will be linear no matter
  what the electron domain is.

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Trigonal Planar Electron Domain

• There are two molecular geometries
• Trigonal planar, if all the electron domains are
  bonding
• Bent, if one of the domains is a nonbonding pair.
• Note Boron is an exception to the octet rule
  and tends to form compounds in which boron has
  fewer than eight electrons around it (an
  incomplete octet).

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Nonbonding Pairs and Bond Angle

• Nonbonding pairs are physically larger than
  bonding pairs.
• Therefore, their repulsions are greater this
  tends to decrease bond angles in a molecule.

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Tetrahedral Electron Domain

• There are three molecular geometries
• Tetrahedral, if all are bonding pairs
• Trigonal pyramidal if one is a nonbonding pair
• Bent if there are two nonbonding pairs

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Trigonal Bipyramidal Electron Domain

• There are four distinct molecular geometries in
  this domain
• Trigonal bipyramidal, if all are bonding pairs
• Seesaw if one is a nonbonding pair
• T-shaped if two are nonbonding pairs
• Linear if three are nonbonding pairs

Note The central atoms in this domain are able
to exceed the octet rule. This is only observed
in those atoms in period 3 of the periodic table
and beyond. The presence of an unfilled d
sublevel in these atoms allows for this behavior.
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Octahedral Electron Domain

• There are three molecular geometries
• Octahedral, if all are bonding pairs
• Square pyramidal if one is a nonbonding pair
• Square planar if two are nonbonding pairs

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Larger Molecules

• In larger molecules, it makes more sense to talk
  about the geometry about a particular atom rather
  than the geometry of the molecule as a whole.

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Valence Bond Theory

• There are two ways orbitals can overlap to form
  bonds between atoms.

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Sigma (?) Bonds

• Sigma bonds are characterized by
• end-to-end overlap.

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Pi (?) Bonds

• Pi bonds are characterized by
• Side-to-side overlap.

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Single Bonds

• Single bonds are always ? bonds, because ?
  overlap is greater, resulting in a stronger bond
  and more energy lowering.

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Multiple Bonds

• In a multiple bond one of the bonds is a ? bond
  and the rest are ? bonds.

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Multiple Bonds

• In a molecule like formaldehyde (shown at left)
  one orbital on carbon overlaps in ? fashion with
  the corresponding orbital on the oxygen.
• The other orbital overlap in ? fashion.

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Multiple Bonds

• In triple bonds, as in acetylene, one orbital
  forms a ? bond between the carbons, and two
  orbitals overlap in ? fashion to form the two ?
  bonds.