Stability in bonding

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Stability in bonding

• In covalent bonds, electrons arent always shared
  equally between the two nuclei.

• This is because some elements have a greater
  affinity for electrons than others.

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Flashback!

• Electronegativity Ability of an atom to attract
  electrons when in a molecule.

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(No Transcript)
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The pull that an element has on electrons
INCREASES as you go from LEFT TO RIGHT and from
BOTTOM TO TOP.
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How does this affect bonds?
H2 has the same amount of pull in both
directions. The bond would look something like
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HF is made of elements from opposite sides of the
periodic table. The fluorine has a much greater
electronegativity than hydrogen (3.98 vs. 2.20).
The electrons would concentrate around the
fluorine, resulting in an asymmetrical electron
distribution between the two nuclei.
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When electrons in a covalent bond are
concentrated near one of the nuclei, the bond is
POLAR.
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If the electrons are shared equally between the
nuclei, the bond is NONPOLAR.
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Now, you try some...
Do the following have polar or nonpolar bonds?
F2
H2O
nonpolar
polar
HCl
C60
nonpolar
polar
polar
polar
BCl3
SO2
S8
BN
nonpolar
polar
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Electronegativity differences greater than 1.7
typically results in the formation of an ionic
bond.
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Both bonds in water are polar. How does this
affect the polarity of the molecule?
O
H
H

• Use arrows along the bonds to indicate the
  direction of the pull on the electrons in the
  bond (the dipole moment).
• A plus-sign on the tail of the arrow shows that
  the bond is more positive at that end

• Add the two vectors (the arrows) together to find
  the net polarity (dipole moment) of the molecule

Because of the bent structure of water, water is
a polar molecule.
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Cl
All of the bonds in CCl4 are polar. Is this
molecule polar?
Cl
Cl
Cl
Since the molecule is symmetrical, all of the
dipoles along the bonds cancel each other
out. CCl4 is a nonpolar molecule and has no net
dipole moment.
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Are these planar molecules polar or nonpolar?
nonpolar
polar
nonpolar
Are these linear molecules polar or nonpolar?
polar
polar
nonpolar