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Chemical Bonds _amp; Reactions

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					Chemical Bonds & Reactions


                    -


          +     +


      -
               Chemical Bond
• A force of attraction that holds two atoms
  together
• Has a significant effect on chemical and physical
  properties of compounds
• involves the valence electrons

     Valence Electrons – the electrons in
     the outermost energy level of an atom
                           -




    This Lithium
                           +
   Atom has one        -       + +
                                     -



  valence electron
Counting Valence Electrons
              -               -               -
                                                               -

                                      -
              -

          +
              +                      ++ +                  +
                                    + + +
-
              +
                  +   -
                          -                       -   -
                                                               + +     -

      +
                                     +  +                          +
          +
              -                       -
                                                               -

                              -               -
              -


     Carbon                                               Beryllium
                                  Oxygen
    4 valence                                             2 valence
                                  6 valence
    electrons                                             electrons
                                  electrons
 How Many Valence Electrons?
• Hydrogen             1 Valence
                        Electron

• Lead           4 Valence
                 Electrons

• Xenon                8 Valence
                       Electrons

                 6 Valence
• Sulfur         Electrons

                       1 Valence
• Rubidium              Electron
          The Octet Rule
• Atoms will combine to form compounds in
 order to reach eight electrons in their
 outer energy level.
  – Atoms with less than 4 electrons tend to lose
    electrons.
  – Atoms with more than 4 electrons tend to gain
    electrons.
  • Be aware that there are some exceptions!

  CONSIDER EIGHT A HAPPY NUMBER FOR
               ATOMS!
                 The Octet Rule In Action
                 6                          7
                      -
                            -
                                    -                   Notice how this chlorine atom has
                                                        seven valence electrons, one away
5
                  -                         -

        -                   -
                                                        from eight. It will try to gain one
                                                        more according to the Octet Rule.
                             +
                             +
                           ++ +
                          ++
             -            +
                          + + ++                -

    -
                          ++ ++
                           +
                                                                                -
4
                                                    -
                            -

                  -                                 1         1
                                                                          -                 -
                                        -

                                -                                 -             -
                      -                 -

                      3                     2
                                                                               + ++
                                                                              + + +
             Notice how the sodium atom has                           -       + +               -

             one valence electron. It is this                                 ++ +
            electron that it will try to get rid                                -

             of according to the Octet Rule.                              -             -
                                                                                    -




            Where do you think Chlorine finds that one electron that it needs?
          Lewis Structure
      (Electron Dot Diagram)
• a way of drawing the outer energy level
  electrons (valence) of an atom
• The symbol for the element surrounded
  by as many dots as there are electrons
  in its outer energy level (valence)
• Examples
                  .              .
                Al :          .N :            Mg :
                                 .           Magnesium
              Aluminum       Nitrogen

  How many valence electrons do each of these atoms have?
            Oxidation Number
• The charge that an atom would have if it
  lost or gained electrons; ionic charge
• Can be helpful in determining which atoms
  will interact or bond with each other
• Example:
                                                            Mg :
  According to electron dot diagram for Magnesium, it
   has two valence electrons. Because Magnesium is          Magnesium
 “unhappy” with two, it will typically lose them. If this
   happens it will turn into a Magnesium ion. At this             2+
      point it will have an oxidation number of +2.
                                                            Mg
What Could the Oxidation Number
              Be?


           H                         O
    +1 or -1 because it can     -2 because it will
    gain or lose one electron   gain two electrons




         Ne                       Sr
      0 because it will not     +2 because it will
     gain or lose electrons     lose two electrons
3 Types of Chemical Bonds

              • Ionic
            • Covalent
            • Metallic

 What can you describe about each of these
   bonds just by looking at the name?
                          IONIC BONDS
• The force of attraction between oppositely charged ions.
• Occurs after a transfer or loss/gain of electrons
• Usually form between atoms of metals and atoms of non-
  metals
• Resulting compounds have a name that usually ends in –ide

   Cl
        1-                                            Na 1+
                     -
                           -
                                  -
                                                                               -
                                                                                           Which
                                                                                         different
             -                        -                               -                     -
                                                                                         groups or
    -                      -                                  -                -          families
                                                                                     of elements will
                          ++ +                                                ++
                                                                                     + most-likely
                                                                                     +
                         + + +                    -               -       +     +               -
        -                                     -
                                                                              +     +   interact to
                          +  +                                                         create these
    -                      -
                                                                               -            types
             -
                                                                      -                  of bonds?
                                                                                          -
                                  -
                                          -                                     -
                           -
                 -
                                 Example - Sodium Chloride (NaCl)
          COVALENT BOND
• A force that bonds two atoms together by a sharing of
  electrons
• Each pair of shared electrons creates a bond
• Usually occurs between atoms of non-metals

                             H O H
                                      -
                         -
                 -              -

                               ++ +           -
             +                + + +               +
                     -         + +                    -
                                -
                         -                -

                     Example – Water (H2O)
      Types of Covalent Bonds
• Different covalent bond types share a different
               number of electrons
    Water (H2O)                           Carbon Dioxide (CO2)                          Nitrogen (N2)
              -       -
                                      -       -                             -       -
                                                                                            -       -          -       -
                  -
                                                                                -
                                                          -
                                          -                                                     -                  -
          ++ +                                                          ++ +
                                                                                                        - -
-     +     + +           -                              ++                                 ++                 ++
                                      ++ +         - -           - -   + + +                            - -   + + +
                          -   +   +                        + +                          +       + +
-         +  +                          + +        - -           - -    +  +                                   +  +
                                                         +  +                               +    +
                                      +  +                                                              - -
                                                                                                -                  -
                  -                       -
                                                          -                     -


          -           -                                                 -           -
                                      -       -


              +




    Single Bonds                                  Double Bonds                          Triple Bonds
      Share 2                                       Share 4                               Share 6
     Electrons                                     Electrons                             Electrons
                Unequal Sharing
                         (Polar Covalent Bond)
• The unequal sharing of electrons between two atoms that
  gives rise to negative and positive regions of electric
  charge
• Results from an atom’s electronegativity – the ability to
  attract electrons to itself

                                                                    ++ +
                   +                                               + + +
     +                           Electron            +
                                  Cloud                             + +

     Bonded hydrogen                                        Hydrogen and
      atoms showing                                       fluorine bond with
      equal sharing of                                    an unequal sharing
         electrons                                           of electrons




               Why do you think the two Hydrogen atoms share
                equally, but the Hydrogen and fluorine do not?
                   Metallic Bond
•   A force of attraction between a positively charged metal ion
    and the electrons in a metal
•   Many metal ions pass along many electrons
•   Many properties of metals, such as conductivity, ductility, and
    malleability, result from the freely moving electrons in the
    metal
•   Usually occurs between atoms of metals



                  Al3+
                   -          Al3+   Al
                                     - 3+       Al3+       Al3+    -
                                                                  Al3+       Al3+   Al3+
                                                                                            Notice
                                                       -                                    how the
                 - Al3+       Al3+       Al3+   Al3+       Al3+   Al3+       Al3+   Al3+
                                     -                                                     electrons
                  Al3+        Al3+       Al3+   Al3+       Al3+   Al3+       Al3+   Al3+    do not
                   -                                                                       just stay
                          -                                              -
                  Al3+        Al3+       Al3+   Al3+   - Al3+     Al3+       Al3+   Al3+   with one
                          -                                        -                          ion
                 - Al3+       Al3+       Al3+   Al3+   - Al3+     Al3+       Al3+   Al3+
         Results of Bonding
         Molecule                             Compound
 A neutral group of two or            A pure substance composed
 more non-metal atoms held            of two or more different
 together by covalent bonds           elements (atoms) that are
                                      chemically combined
Type:
                                               Examples:
 Diatomic - molecules                        CO, NO2, NaCl
 consisting of two atoms of
 the same element bonded
 together
         Examples:
       H2, F2, O2, N2



              What would you call something that has
                    characteristics of both?
Molecule, Compound, or Both?
  Chemical Reaction Basics
         H2 + O2 --> H2O
           Reactants           Products




Reactants- substance that enters into a reaction

Products- substance that is produced by a chemical
reaction
         Chemical Equation
• Shorthand form for writing what reactants are
  used and what products are formed in a chemical
  reaction
• Sometimes shows whether energy is produced or
  absorbed
• Examples:
                2H2 + O2  2H2O

           CH4 + 2O2  CO2 + 2H2O

     C6H12O6 + 6O2  6CO2 + 6H2O + energy
         Components of a Chemical
                Equation
               Chemical                               Chemical
               Formulas                                Formula



       2H2 + O2                                  2H2O
Coefficient                                                  Subscript
                  Subscripts                       Coefficient

                                  (Yield)
         (Reactants)                             (Products)

                                                                 
  Sometimes you will see a “yields” sign that looks like this.
                                                                 
                                                                 
                                                                 
                                                                 
               What do you think it means?
Energy and Chemical Reactions
     Exothermic Reaction                    Endothermic Reaction

• A chemical reaction in               • A chemical reaction in
  which energy is released.              which energy is absorbed.
• The products have greater            • The products have lower
  bond energy than the                   bond energies than the
  reactants                              reactants

C6H12O6 + 6O2  6CO2 + 6H2O + energy      CO2 + H2O + energy  C6H12O6 + O2
              (respiration)                       (photosynthesis)

                    Chemistry Comes Alive! Sample Movies
                           TeacherTube - Videos
                      Chemistry Demonstration Videos
              Can you think of other reactions where
                   energy is gained or released?
            Chemical Reaction
• The process by which a                What does
  chemical change occurs                H2 & O2 gas
• Atoms are rearranged, and              create?
  chemical bonds are broken and
  reformed
• One or more substances change
  to produce one or more
  different substances
• Types
   –   Synthesis (creating)
   –   Decomposition (separating)
   –   Combustion (burning)
   –   Displacement/Replacement
       (switching)
  Out of the four types of reactions,
  which would describe the chemical
  reaction taking place to the right?

                                        H2            O2
  You can think of atoms as people
    getting together as couples...


Analogy              Chemical Reaction
One person           An ion or element
A couple             A compound
Switching partners   A replacement reaction
The Get Together…
Synthesis
Decomposition
Decomposition
Single Replacement Reactions
Single Replacement Reactions
Double Replacement Reaction
Double Replacement Reaction
Combustion
       Types of Reactions
          Romance Chemistry :)

Synthesis- Marriage/Dating
     A + B = AB
Decomposition- Divorce/Breakup
     AB= A + B
Single-Replacement- Dance Cut In
     AB + X = AX + B
Double-Replacement- Dancing Couples
  switch partners.
     AB + XY = AY + XB
  Types: Synthesis
 Example C + O2  CO2

C + O O       O C O



General:   A + B  AB
Types: Decomposition
Example: NaCl  Na + Cl


Cl Na       Cl   +   Na



General:    AB  A + B
Types: Single displacement
Example: Zn + CuCl2  ZnCl2 + Cu


      Cu      + Zn  Cl Zn Cl + Cu
 Cl        Cl



 General:       AB + X  AX + B
Types: Double displacement
Example: MgO + CaS  MgS + CaO


 Mg        Ca        Mg       Ca
      +                    +
 O         S          S        O


General:       AB + XY  AY + XB
  Law of Conservation of Mass
• Atoms cannot be created or destroyed in a
  chemical reaction.
• What goes in must come out.
• So we must balance equations to conserve
  mass.
      Law of Conservation of Mass
• Proposed by Antoine Lavoisier
• In a chemical reaction, atoms are neither created nor
  destroyed
• All atoms present in the reactants are also present in
  the products
• Chemical equations must account for/show the
  conservation of mass  balancing equations

     In its present form, does this chemical equation show a
                      conservation of mass?



     2 H2 + O2  2 H2O
  Reactants                                                Products

  H 2
     4        How would you balance this equation to       H 2
                                                              4
  O 2
     2           show the conservation of mass?            O 1
                                                              2
           Balancing Equations
• Rules:
   – We can not add or subtract subscripts from either side
     of the equation
   – We can only add coefficients to the front of each
     compound
• Ex. 2H2 + O2 --> 2H2O
              H=4                H=4
              O=2                O=2

                Before   must match   After

           See “Balancing Act” worksheet for more examples…
 Hints For Balancing Equations
• Count the atoms
   – List the number of atoms of each element to see which
      elements must be balanced
• Use a coefficient to add atoms to one side of the equation
   – Start with the reactant or product that has the
      greatest number of different elements
• Add a coefficient to another reactant or product
   – Make sure that the coefficients in your balanced
      equation are the smallest whole numbers possible (they
      should have no common factor other than one)


              Tutorial on Balancing Equations

				
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