Unit 10 Covalent Bonding Chapters 8 9 Chemistry 1L Powerpoint Templates Cypress Creek High School Ionic Properties Review • Ionic Bonds Pro by hcg20920

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									     Unit 10:
 Covalent Bonding

     Chapters 8 & 9
      Chemistry 1L
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Cypress Creek High School
Ionic Properties Review
         • Ionic Bonds Properties:
             – Exhibit a crystal structure
             – Exist as solids
             – Dissolve easily in water
             – Have high melting and
                boiling points
             – Conduct electricity in
             – Have high electronegativity
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Covalent Compound Properties
            • Properties of Covalent Compounds
               – Have low melting and boiling
               – Do not dissolve easily in water
               – Do not conduct electricity in
               – Exist as gases, liquids, or solids
               – Have low electronegativity

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   Common Covalent Compounds
Nitrous oxide (N2O) is laughing gas used as an
                                                    Methane (CH4) is a flammable gas used
anesthetic and to boost auto engine power
                                                    as fuel and in homes for domestic heating
                                                    and cooking purposes.

                       Sugars, like sucrose (C12H22O11)
                       and glucose (C6H12O6), are used
                       in food and energy production

                                          Hydrogen peroxide (H2O2) is used as a bleaching
                                          agent, emetic (induces vomiting), and an antiseptic
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                                          (clean cuts and scrapes)
Common Covalent Compounds:
    Carbon dioxide (CO2) is a gas used by plants during
    photosynthesis, produced in respiration; it is a byproduct
    of burning fossil fuels, and it has many uses as a fire
    extinguisher, refrigerant (dry ice), and carbonation in

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  Common Covalent Compounds:
Water (H2O) is a liquid that is vital for life. It covers about 71% of
earth’s surface, and makes up about 60% of the human body. It is
known as the universal solvent, and has many unique properties and

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                Covalent Bonds
 • A Covalent Bond occurs when valence electrons are shared
    between atoms (usually between nonmetallic elements)
 • Covalently bonded compound known as a molecule
     – These shared electrons are part of the valences of all
       atoms involved (satisfies octet rule)
                             • Since electrons are shared, no
Carbon Dioxide
                               charges appear
                             • Many combinations can occur
                               between two nonmetals
                                 – Example: carbon and oxygen
                                   can form carbon monoxide
                                   (CO) and carbon dioxide
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Single Covalent Bonds
      • A Single Covalent Bond occurs
        when atoms of some elements
        attain a noble gas
        configuration by sharing one
        pair of electrons between two
      • When drawing these
        molecules, a line can represent
        a pair of shared electrons
          – Ex: Methane (CH4)
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Multiple Covalent Bonds
              • Sometimes, atoms share more
                than one pair of electrons
                between two atoms creating
                multiple covalent bonds
              • When drawing these
                molecules, multiple lines can
                represent pairs of shared
                  – Ex: diatomic oxygen (O2) and
                    nitrogen (N2)

     How many pairs of electrons does each kind of bond share?
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                                                     3 pairs
     Single: _________ Double: _________ Triple: _________
               1 pair             2 pairs
          Diatomic Elements
• Some nonmetal elements on the periodic table exist
  in nature only as pairs called diatomic molecules;
  bonded covalently
   – H, O, F, Br, I, N, Cl

                      Hydrogen Molecule (H2)
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                Covalent Nomenclature
                         • Naming (for covalent with 2 elements):
                            – Name the 1st element with prefix to
                              indicate the # of atoms (only if more than
                            – Name the 2nd element
                                • Use prefix to indicate the number of
                                  atoms present
                                • Drop the ending of the elements name
                                  and use “ide” ending
                            – Example: NCl3 = nitrogen trichloride
  1         2      3        4      5       6       7      8      9      10
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mono-       di-   tri-    tetra- penta- hexa-    hepta- octa-   non-   deca-
     Covalent Nomenclature
        Name                                   Formula

diphosphrous pentoxide                          P2O5

 dinitrogen monoxide                             N2O
  sulfur hexafluoride                            SF6

   oxygen dichloride                            OCl2

  dinitrogen trioxide                           N2O3

   carbon monoxide      Powerpoint Templates    CO
     Types of Electron Sharing
  • Covalent bonds share electrons equally
    and unequally (“tug of war” with electrons)
    – Which molecule appears “balanced”? H2O
    – Which one does not? O2
Water (H2O)
                                         Oxygen (O2)

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             Unequal Sharing
• Unequal sharing of electrons occurs when
  atoms that share electrons have different
  electronegativities and are called polar bonds
  – Shared electrons spend a greater amount of time
    at the more electronegative atom
     • Example: water (H2O)

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             Unequal Sharing
• Symbols, delta plus
  and delta minus,
  represent a partial
  positive charge and a
  partial negative charge.

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  Unequal Sharing Example:
            H2 O
• Water Molecule Animation

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              Equal Sharing
• Equal sharing of electrons occurs in non-
  polar covalent bonds
   – No difference (or very, very small
     difference) in electronegativity between
     atoms that are sharing
     • Example: chlorine (Cl2)

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   Bonding & Electronegativity
• Atoms bond according to the difference in their
• Look at table of EN values and find the difference
  between the two atoms involved (absolute value)
• If EN difference is…
                       >1.7 = ionic bond
                       0.5 – 1.7 = polar covalent bond
                       < 0.5 = nonpolar covalent bond

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Bonding & Electronegativity

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   Bonding & Electronegativity
• Try to predict the bond type (ionic, polar
  covalent, nonpolar covalent) using your EN
 Formula   EN values     EN Difference      Bond Type

            Li = 1.0
 LiCl       Cl = 3.0
                             2.0           ionic bonds

           P = 2.1                       polar covalent
 PCl3      Cl = 3.0         0.9              bonds
           Mg = 1.2                       ionic bonds
 MgO       O = 3.5          2.3
           C = 2.5                          nonpolar
  CH4      H = 2.1          0.4          covalent bonds
           N = 3.0                     polar
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  NF3      F = 4.0                         bonds
            Molecular Shapes
• Applies to covalent compounds only.
• Use VSEPR steps (valence shell electron pair repulsion):
   – 1) Identify the central atom as the element that can
     form the most bonds
   – 2) Draw the Lewis dot structure for the molecule
   – 3) Count total # of electron pairs around the central
      – 4) Count # of bonding pairs of electrons around the
         central atom
              – 5) Count # of lone pairs of electrons around
                 the central atom
              – 6) Look at summary chart, identify shape
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                        Molecular Shapes
# of e- pairs around   # of bonding    # of lone
    central atom        pairs of e-   pairs of e-       Name         Shape

         2                  2             0             linear

         3                  3             0

         4                  4             0          tetrahedral

         4                  3             1

         4                  2             2         angular (bent)

         4                  1          Powerpoint Templates
                                         3          linear
Exceptions to Octet Rule
   • Beryllium
     – Has 2 valence electrons
     – Full with 4 valence electrons
     – Ex: BeI2
   • Aluminum
     – 3 valence electrons
     – Full with 6 valence electrons
     – Ex: AlCl3
   • Boron
     – 3 valence electrons
     – Full with 6 valence electrons
     – Ex: BH3
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     Molecular Shape Example
•   What is the shape of water (H2O)?
•   1) Central atom? oxygen
•   2) Draw Lewis Dot…
•   3) # of total electron pairs around central atom?
               • 4) # of bonding pairs around central
                  atom? 2
               • 5) # of lone pairs around central
                  atom? 2
               • 6) Refer to chart to identify
                  shape…angular (bent)
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       Molecular Shape Prediction
  • Try to predict the shape using VSEPR and
    your shape chart:
            1) BCl3     2) CH4 3) NH3
   Lewis Dot

  Central Atom

     # e- pairs

# bonded pairs

  # lone pairs
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• Just because you
  have polar bonds,
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   Polar & Nonpolar Molecules
• Polar molecules have a partial positive and partial
  negative charge – called a dipole
• Molecules are considered polar if they:
   – Have an asymmetrical shape
      • Has a lone pair of electrons
                    – trigonal pyramidal
                    – linear (with 2 different elements)
                    – angular (bent)
                 • Has Polar Bonds AND has different
                    elements around the central atom
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• The molecule is non-polar due to the
  symmetrical shape of the molecule but it
  does contain polar bonds. YOU CAN HAVE
              Polar bonds             H
                             H        C H
               Powerpoint Templates   H
• The electrons are no longer being pulled
  with equal force nor in equal directions.

           H           C Cl
                       H                Different
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       Polar & Nonpolar Molecules
  *IMPORTANT: Polar & nonpolar molecules are
    different from polar & nonpolar bonds!!!
Non-polar molecules have charges
that are evenly distributed, due to
shape (ex: any diatomic molecule,

                                           Polar molecules have a partial positive
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                                           and a partial negative charge (ex: water)
      Property          Ionic Bonds         Covalent Bonds
    Electrons are:      Transferred                   Shared
   Difference in                                  <0.5 nonpolar
   Electronegativity:                             0.5 to 1.7 polar

    Bond between:       A metal and                2 nonmetals

    State at room         Solid             Solid, Liquid, or Gas

   Particle Name:       Formula Unit                Molecule

   Melting Point:          High                       Low

Conducts Electricity?      Yes                         No

Dissolves in water?        Yes                    No (usually)

                            No                        Yes
Forms a more stable        Yes                        Yes

    Examples:             NaCl, MgI2              NH3, CHCl3
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• Polymers are large molecule
  (macromolecule) usually composed
  of a repeating pattern of atoms
  covalently bonded together
• Plastics are the most easily identified
  polymers there are many natural
  biopolymers such as:
   – proteins
   – nucleic acids
   – carbohydrates
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    THE END.

Be Prepared for
 Unit 10 Test.

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