CHEMICAL BONDING Chapter 3

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					                        CHEMICAL BONDING

BASIC IDEA - all elements want to be like the noble gases and have their outermost shell filled
with electrons. To achieve this goal atoms will (1) share electrons (covalent bonding),
(2) give away electrons (ionic bonding), or (3) take electrons (ionic bonding).

Covalent Bonding
Atoms share electrons

 H  +  H ------> H H           or H—H      or H2 hydrogen gas

By sharing their electrons, the Hydrogen atoms have the s shell filled. They ‘feel’ like the noble
gas, helium.

A single bond means 2 electrons are shared

          H -- H

A double bond means 4 electrons are shared

                     H      H
                       C = C                           ethene
                     H       H

A triple bond means 6 electrons are shared.

          H-C  C-H

Valence electrons - electrons available for bonding

+1 Column I of chart has 1 electron
+2 Column II of chart has 2 electrons
+3 Column III of chart has 3 electrons
 4 Column IV of chart has 4 electrons
-3 Column V of chart has 5 electrons
-2 Column VI of chart has 6 electrons
-1 Column VII of chart has 7 electrons

H Br           H has one electron on outermost level or shell. Br has 7 electrons on outermost
level or shell

                 H    Br       =         H-B


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Ionic Bonding
Atoms either gives away or takes electrons - no sharing.

         NaCl Sodium (Na) has 1 electron on the outermost shell. Chlorine (Cl) has 7
electrons on the outermost shell. If Na gives away 1 electron, it will feel like the noble gas,
Neon. If chlorine accepts the electron, it will have 8 on its outermost shell and feel like the noble
gas Argon (Ar).

       Na       Cl   ----->           Na+1            Cl-1

 Na+ Cl- Na is short one negative charge. Cl got it.

Positive ions are called cations.
Negative ions are called anions.
Most ionic compounds are solids.
Metals lose electrons.

 CaCl2 ----->    Ca+2    Cl-1
                                      Ca gives away 2 electrons.
Calcium chloride                      Each chlorine atom takes 1.



ION SIZES

Metals - The ion has a smaller diameter than the atom of a given metal.


     Sodium atom                              Sodium ion

Nonmetals - The ion has a larger diameter than the atom of a given nonmetal.



 Chloride atom                                Chloride ion

IONS MUST HAVE

 1. A metal and a non metal
 2. Metal loses electrons
 3. Nonmetal gains the electrons
 4. The number of electrons given up by the metal must equal the number of electrons picked up
       by the nonmetal so the compound has no net charge.


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Nomenclature

 The metal is written first. NaCl
 Say the metal Sodium
 Add the suffix 'ide' to the non metal Sodium chloride

 hydride, carbide, fluoride, iodide, nitride, oxide, phosphide sulfide.


COVALENT BONDING

If an atom can't give away its electron easily and another atom can't accept it, the two atoms will
share their electrons.

Elements or compounds would like to have 8 electrons. The electrons involved in bonding are
called valence electrons. The periodic chart gives us an idea of how the elements will react with
each other.

Chemical Formula


H2O            2 hydrogens at +1                      (+1) (2) = +2
               1 oxygen at -2                         (-2) (1) = -2
                                                      net         0


NH3            1 nitrogen at -3                       (-3) (1) = -3
Ammonia        3 hydrogens at +1                      (+1) (3) = +3
                                                        net       0

carbon tetrachloride CCl4

                               carbon C = +4          (+4) (1) = +4
                              chloride Cl = -1        (-1) (4) = -4
                                                  net             0

CO2            C = +4                                 (+4) (1) =      +4
               O = -2                                 (-2) (2) =      -4
                                                  net         0

We have been working with oxidation numbers. Oxidation number or oxidation state is used to
tell us the positive or negative character of an atom. When electrons are removed or shifted away
during a reaction, the atom is assigned a positive oxidation number.



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This also works for the ionic compounds

Al2O3 Means we have 2 aluminum atoms and 3 oxygen atoms

               Al is +3 on chart                     (+3) (2) = +6
               O is -2 on chart                      (-2) (3) = -6
                                                       net       0

Na+1 Mg+2

When electrons are gained, the element is given a negative oxidation number. Cl-1
      O-2

The algebraic sum of the positive oxidation number and the negative oxidation number of the
atoms and ions present in a compound must always be zero.

                 MgO CaBr2


Polar vs Non Polar Covalent Bonding

Some atoms will have a greater strength for pulling electrons to itself than other atoms.
Sometimes in sharing (covalent) electrons one of the atoms has a greater pull on the electrons.
Electrons have a negative charge. So the atoms that can pull the electrons strongly have a greater
electronegativity value.

Electronegativity Values

  H
 2.1

  Li     Be     B      C       N       O    F
 1.0     1.5   2.0    2.5     3.0    3.5 4.0


 Na    Mg        Al   Si       P       S     Cl
 0.9   1.2      1.5   1.8     2.1   2.5    3.0


  K    Ca                                   Br
 0.8   1.0                                 2.8
  If the difference between two electronegativity values is
         1.7 or greater we get ionic compounds

  If the difference is zero we have non polar covalent



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  If the difference is greater than zero and less than
         1.7 we get polar covalent bonds.



ELEMENTS AND OXIDATION NUMBERS

Look at the chart for most of the numbers.
Most commonly used elements:
               H       +1                       F        -1
               Na      +1                       Cl       -1
               K       +1                       Br       -1
               Mg      +2                       O        -2
               Ca      +2                       S        -2
               Al      +3                       N        -3
               C       +4                       P        -3

Radicals - Ions

( ) Everything inside the brackets stays together and acts as an "element" - ion.

(NH4)+1                     Ammonium ion

(OH)-1                  Hydroxide ion           H(OH) - water

(NO3)-1           Nitrate

(CO3)-2           Carbonate

(SO4)-2           Sulfate

(PO4)-3      Phosphate
Nomenclature

 Do the element on the left first Mg(SO4)

                                         Magnesium sulfate


Sometimes you can have two elements come together in more than one ratio.

  NO                        N2O                          N2O3

nitrogen monoxide           dinitrogen monoxide dinitrogen trioxide


                                                                                    5
1 mono-          2 di- 3 tri-     4 tetra-   5 penta-   6 hexa-

 7 hepta- 8 octa- 9 ennea- 10 deca-
We will work primarily with just one or two values. For example oxygen will be -
2       carbon +4 or -4       hydrogen +1 or -1

nitrogen +5 or -3


Let's see what the formulas of the following would be.


What would the formula be for sodium carbonate?

Na(CO)3          Na+1     (CO3)-2

          Na2(CO3)      Na2+1(CO3)1-2
          +2 -2          =      0

(NH4)(OH)       Is it balanced:

Ca     (NO3)

Na     (NO3)

Na     (SO4)

Ca      (PO4)

Al     (SO4)



Multiple Valences for Metals

Fe     Iron      +2, +3           Ferrous +2     Ferric +3

Cu     Copper +1, +2              Cuprous +1     Cupric +2

Hg     Mercury +1, +2             Mercurous +1 Mercuric +2

Sn     Tin +2, +4                 Stannous +2    Stannic +4


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Pb     Lead +2, +4            Lead II Lead IV


Write the formulas using the appropriate subscripts:

Stannic chloride
Mercurous oxide
Cupric oxide
Barium chloride
Potassium chloride
Ferrous chloride
Cuprous oxide
Ferric oxide
Stannous chloride

Find the oxidation state of Mn in the compound KMnO4 . Given K = +1 O = -2


BALANCING EQUATIONS

No quick, easy way. Requirements: pencil + eraser + patience
The number of atoms on the left side of the equation has to equal the number of
atoms on the right side of the equation.
                                             Left           Right
Na + O2 -----> Na2O              Why?       1 Na            2 Na
                                             2O             1O
2 Na + O2 ---->        Na2O                2 Na           2 Na
                                             2O              1O
2 Na + O2 ----> 2 Na2O                     2 Na              4 Na
                                             2O              2O
4 Na + O2 -----> 2 Na2O                      4 Na            4 Na
                                             2O             2O

When balancing equations LEAVE THE SUBSCRIPTS ALONE, work with the
coefficients.

1. In Al2(SO4)3
       a) the number of atoms of Al is _____.

       b) the number of atoms of S in the formula is _____.

       c) the number of atoms of oxygen in the formula is ______.



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2. Balance the following equations: [*H2O can also be written as H(OH)]

(a)    ____H2 + ____ N2      ------->   ____NH3

(b)    ____C3H6 + ___O2 -------->       ____ CO2    + ____ H2O

(c)    ____ Na + ____ HCl ------> ____ Na Cl         + ____ H2

(d)    ____ Na + ____ H2O -------> ____ NaOH + ____ H2

(e)    ____HCl + ____ NaOH -------> ____NaCl + ____ H2O*

(f)    ____ HCl + ____Ca(OH)2 -------> ____CaCl2          + ____H2O*

(g)    ____H2(SO4) + ____Na(OH) ------> _____Na2(SO4) + ____H2O*

(h)    ____H2(SO4)    + ___ Ca(OH)2     -------> ____ Ca(SO4)       + ___H2O*

(i)    ____Al + ___H(NO3) -------> ____ Al(NO3)3          +       ____ H2

(j)    ____ Fe + ____ H2(SO4) -------> ____ Fe(SO4)           +    ____ H2




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