Atomic Structure and Ionic Bonding (A Visual Approach)

David Harazin                  Jamieson Elementary School
                               5650 N. Mozart
                               Chicago IL 60629
                               (312) 534-2395

Objectives:

     The 8th grade student will be able to:
          1.  Determine the number of protons, neutrons and electrons
              for a given element by using the periodic table.
          2.  Construct and draw models and diagrams of atoms.
          3.  Use the concept of the stable octet to predict simple
              molecular formulas.
          4.  Distinguish between elements and compounds.

Materials Needed:

     4 boxes of round toothpicks (250 in box)
     1/4 inch round blue self-adhesive labels
     1/2 inch round green self-adhesive labels
     1/2 inch round red self-adhesive labels
     one bag large white marshmallows
     three bags mini-marshmallows (these come in four colors)
     one square sheet (at least 6 inches square) aluminum foil
     one piece of white chalk

*  These materials were used for a class size of 20.  *

Strategy:

     Use the aluminum foil and the white chalk to explain the difference between 
compounds and elements.  (For this demonstration we are assuming that the foil 
is made only of aluminum and the chalk is pure calcium carbonate.)  This can be 
done by utilizing the physical properties of these substances (for example: 
melting point/ boiling point).  Explain that the aluminum is made of similar 
atoms with similar properties and that the chalk is made of different atoms 
(carbon, oxygen, calcium).  If you separated these different atoms from the 
chalk, they would have different properties.  Since the aluminum is made of only 
one type of atom we call it an element.  It cannot be broken down into smaller 
pieces.  The chalk can be broken down into smaller parts or atoms.  Therefore, 
it is called a compound. 
     After defining an element and an atom, describe the parts of the atom 
starting with the proton and neutron.  This should lead into an explanation of 
the atomic number and the mass number.  Use the toothpicks, large white 
marshmallows and mini-marshmallows to build a three-dimensional model of an 
atoms nucleus.  The large white marshmallow is used to hold the nucleus 
together.  It should be explained that a real nucleus does not have a different 
substance in its center but is composed of only protons and neutrons.  The 
toothpicks are inserted into the large white marshmallow so that two ends of the 
toothpick are sticking out.  The mini-marshmallows are then placed on the ends 
of the toothpick so two mini-marshmallows may be added with one toothpick.  
Students should choose only two colors of mini-marshmallows, one to represent 
protons and one to represent neutrons.  The toothpicks may also be broken in 
half to add only one mini-marshmallow to a vacant place on the large white 
marshmallow.  Use flashcards with the elements symbols (this will introduce the 
symbols used for atoms) and have students select a nucleus to build.  There 
should be only one symbol per flashcard (A large marshmallow will hold 
approximately fifty mini-marshmallows.) 
     The self-adhesive labels are used to construct two-dimensional models of 
the entire atom.  An explanation of neutrality and placement of electrons must 
be given prior to this activity.  Also, elements for this section must be 
selected in pairs from elements 1 through 18 so that each pair, when bonded, has 
a total of eight valence electrons.  These elements will be used for bonding.  
Models will be constructed on paper with the red and green circles in the center 
representing protons and neutrons and the smaller blue dots around the center or 
nucleus representing electrons.  It may be helpful to draw three concentric
circles on the paper to represent the respective orbitals.  This will help 
students place the electrons in the correct orbital. 
     When the two-dimensional models are finished, explain that atoms like to 
bond so that the total number of outer electrons in the compound is equal to 
eight.  Have students find a partner in the room to bond with so that the total 
number of outer electrons forms this stable octet.  This can lead into a 
discussion about the stable octet and valence electrons.  The number of valence 
electrons is also listed at the top of each group on the periodic table.  Let 
students discover this. 

Performance Assessment:

     Before the bonding activity, use the two-dimensional models to play a game.  
Hang the models on the walls of the room and have students guess which atom each 
student constructed.  Student should only have their name on the model NOT THE 
ATOM'S NAME.  Students should be able to list the number of protons, neutrons 
and electrons to determine the element.  When the game is finished you can see 
which students constructed models correctly and which students were able to 
utilize their knowledge to "guess" or identify the other atoms. 

Conclusion:

     In doing the activity, students will see trends in the periodic table that 
were not discussed.  For example, students may observe that the atomic nucleus 
gets larger as the mass number gets larger.  They may also discover that all the 
elements in a particular group have the same number of valence electrons. 
     Additionally, this activity could be used to inspire artistic creativity by 
allowing students to construct models of atoms using materials that they choose 
and bring in from home.  Students may also modify the existing activity; for 
example, they may choose not to fasten the mini-marshmallows with toothpicks but 
may want to try gluing the marshmallows together with rubber cement.