Chapter 23 Chemical Bonding by phf13063

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									   Chapter 23
Chemical Bonding
23.1 – An Atomic Model is Needed to
    Understand How Atoms Bond
• Review shell model of atom (18.4)
• Valence electrons –
• Electron Dot Diagrams –
  – Tells valence electrons
  – How many (ve) are paired
• Nonbonding pairs -
Electron Shells
K=
L=
M=
N=
O=
P=
Q=
   23.2 – Atoms Can Lose or Gain
  Valence Electrons to Become Ions
• Atoms are electrically neutral
   – Why?
• Ions are not electrically neutral
   – Why?
• Ion –
   – Can be negative or positive
• Atoms tend to lose or gain electrons so they
  end up with an outermost occupied shell that
  is filled to capacity
• The Periodic table can be used to determine
  the type of ion that an atom tends to form
Positive Ion (cation)




Negative Ion (anion)
 23.3 – Ionic Bonds Result from an
   Transfer of Valence Electrons
• Result of transfer of electrons forms a
  positive ion and a negative ion
• Ionic Bond –
• Ionic Compounds –
• Characteristics of Ionic Bonds -
Ionic Bonds: One big greedy thief dog!
Ionic bonding can be best imagined as one big
greedy dog steeling the other dog's bone. If the
bone represents the electron that is up for grabs,
then when the big dog gains an electron he
becomes negatively charged and the little dog
who lost the electron becomes positively
charged. The two ions (that's where the name
ionic comes from) are attracted very strongly to
each other as a result of the opposite charges.
23.4 – Covalent Bonds Result from a
    Sharing of Valence Electrons
•   Covalent bond –
•   Covalent Compound –
•   Molecule –
•   Characteristics of Covalent Bonds –

• Can be single, double, or triple
Covalent Bonds: Dogs of equal strength.
Covalent bonds can be thought of as two or more dogs
with equal attraction to the bones. Since the dogs
(atoms) are identical, then the dogs share the pairs of
available bones evenly. Since one dog does not have
more of the bone than the other dog, the charge is
evenly distributed among both dogs. The molecule is
not "polar" meaning one side does not have more
charge than the other.
 23.5 – Polar Covalent Bonds Result
from an Uneven Sharing or Electrons
• Dipole –
• Electronegativity –
  – Difference in electronegativity
• Nonpolar Bond –
• Polar Bond -
Polar Covalent Bonds: Unevenly matched but
willing to share.
These bonds can be thought of as two or more
dogs that have different desire for bones. The bigger
dog has more strength to possess a larger portion of
the bones. Sharing still takes place but is an uneven
sharing. In the case of the atoms, the electrons spend
more time on the end of the molecule near the atom
with the greater electronegativity (desire for the
electron) making it seem more negative and the other
end of the molecule seem more positive.
23.6 – Molecular Polarity Results from an
    Uneven Distribution of Electrons
• Polar and nonpolar are easy when 2 atoms,
  more complex when more than 2 atoms are
  bonded
• End result may be a even distribution or an
  uneven distribution
• Can make the dipole stronger
• Explains why water is “sticky”
• May explain other macroscopic properties
This molecular polarity causes
water to be a powerful solvent
and is responsible for its strong
surface tension. The molecular
arrangement taken by ice (the
solid form of the water molecule)
leads to an increase in volume
and a decrease in density.
Expansion of the water molecule
at freezing allows ice to float on
top of liquid water.

								
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