Covalent Bonding

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Covalent Bonding
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Covalent Bonding

• Electrons are shared between two nonmetals
• Weaker attractive force than ionic bonding

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Properties of Molecular Compounds
State at SATP Typically gases liquids, but some solids
Structure Variable (waxy to brittle)
Melting Boiling Points Low
Electrical Conductivity Nonelectrolyte
Solubility in Water Variable (low to high)
Confused?? Dont worrymore answers to come
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Covalent Bonding
Lone pairs, valence electrons not involved in
covalent bond

• Formation of hydrogen chloride

H - Cl



Covalent bond, shared electrons
Structural Formula H-Cl (lone pairs are not
drawn)
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Lewis Structures
H2
Cl2
Structural Formula Cl-Cl
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Double and Triple Bonds

• Atoms can share 4 electrons to form a double
  bond or 6 electrons to form a triple bond.

O2
N2

• The number of shared electron pairs (covalent
  bonds) that an atom can form is the
• bonding capacity.

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Multiple Covalent Bonds


N


N




8
Multiple Covalent Bonds



O
C

O








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Drawing Lewis Structures

• Arrange the element symbols.
• Central atoms are generally those with the
  highest bonding capacity.
• Carbon atoms are always central atoms
• Hydrogen atoms are always peripheral atoms
• Add up the number of valence electrons from all
  atoms.
• For polyatomic ions, add one electron for each
  negative charge and subtract one for each
  positive charge.
• Draw a skeleton structure with atoms attached by
  single bonds.
• Complete the octets of peripheral atoms.
• Place extra electrons on the central atom.
• If the central atom doesnt have an octet, try
  forming multiple bonds by moving lone pairs.

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Practice Problems

• Examples
• Methanal CH2O
• Chlorate (polyatomic ion)
• p.77-81 1-15

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Strategy for Writing Lewis Structures
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• Draw Lewis structures and the structural formula
  for

H F
HF



H2O
NH3
CH4
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Molecular formula
For NF3
Atom placement


N 5e-
F
F





Sum of valence e-
F 7e-
X 3 21e-
N
Total 26e-
F



Remaining valence e-
Zero NF3 is uncharged
Lewis structure
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SAMPLE PROBLEM 10.1
Writing Lewis Structures for Molecules with One
Central Atom
SOLUTION
Cl
Step 1 Carbon has the highest bonding capacity
and is the central atom. The other atoms are
placed around it.
C
Cl
F
F
Steps 2-4 C has 4 valence e-, Cl and F each
have 7. The sum is 4 4(7) 32 valence e-.
Make bonds and fill in remaining valence
electrons placing 8e- around each atom.
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SAMPLE PROBLEM 10.2
Writing Lewis Structure for Molecules with More
than One Central Atom
SOLUTION
Hydrogen can have only one bond so C and O must
be next to each other with H filling in the
bonds. There are 4(1) 4 6 14 valence
e-. C has 4 bonds and O has 2. O has 2 pair of
nonbonding e-.
H

C
O
H
H

H
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SAMPLE PROBLEM 10.3
Writing Lewis Structures for Molecules with
Multiple Bonds.
PROBLEM
Write Lewis structures for the following (a)
Ethylene (C2H4), the most important reactant in
the manufacture of polymers (b) Nitrogen (N2),
the most abundant atmospheric gas
PLAN
For molecules with multiple bonds, there is a
Step 5 which follows the other steps in Lewis
structure construction. If a central atom does
not have 8e-, an octet, then e- can be moved in
to form a multiple bond.
SOLUTION
(a) There are 2(4) 4(1) 12 valence e-. H
can have only one bond per atom.

(b) N2 has 2(5) 10 valence e-. Therefore a
triple bond is required to make the octet around
each N.
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Polyatomic Ions

• Many compounds contain a combination of covalent
  and ionic bonds.
• E.g. NaOH
• OH- is a polyatomic ion with a covalent bond
  between O and H
• Ionic bond between Na and OH-

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Coordinate Covalent Bonds

• A covalent bond in which both of the shared
  electrons come from the same atom.
• E.g. NH3 (ammonia) and H (hydrogen ion) to form
  NH4 (ammonium)

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Drawing Lewis Structures



COCl2
24 ves








14 ves
HOCl



?





26 ves
ClO3?






CH3OH
14 ves