Beacon Lesson Plan Library

Let Us Bond Together

Warren Bell

Description

Students learn about bond strengths/bond types by observing a demonstration. They apply this knowledge in their own experiments so they can predict bond strengths/bond types based on the locations of the bonding atoms on the periodic table.

Objectives

The student knows that the vast diversity of properties of materials is primarily due to variations in the forces that hold molecules together.

The student knows that connections (bonds) form between substances when outer-shell electrons are either transferred or shared between their atoms, changing the properties of substances.

The student knows that elements are arranged into groups and families based on similarities in electron structure and that their physical and chemical properties can be predicted.

Materials

-Six (6) large rubber bands
-Two (2) pulleys with clamps
-Two (2) 1000 gram sets of weights
-Two (2) ring stands
-Two (2) hooked vector weight holders
-One (1) box thumb tacks per group
-One (1) box round toothpicks per group
-Thirty (30) styrofoam balls per group
-Six (6) pipe cleaners cut into 3 inch pieces per group
-Twenty (20) regular rubber bands per group
-One (1) copy of periodic table per student
-One (1) copy of study sheet/activity sheet per student

Preparations

1. Assemble all equipment necessary for the demonstration:
a) Attach the pulleys to the ring stands and place them approximately six inches apart.
b) Stretch a single, twisted, large rubber band across the six inch distance threading through the pulleys and then attaching a hooked, vector weight holder to each end of the rubber bands.
c) Place a 1000 gram weight set beside each pulley system to add weights to both sides until the rubber bands break (practice so that you know approximately how much weight it will take to break each set of rubber bands). Repeat the set-up and running of the demonstrations for double twisted and triple twisted rubber bands.

2. Pre-select the ten elements from the periodic table to be used to predict the electronegativity values before doing procedure #3 of the first day's activities.
NOTE: The ten elements selected should be different from those given on the student's activity sheets as the demonstrations will act as examples for the students to follow.

a) Francium
b) Iodine
c) Neon
d) Nickel
e) Phosphorous
f) Strontium
g) Silver
h) Antimony
i) Carbon
j) Hydrogen

3. Pre-select the ten pairs of elements whose bond types are to be predicted and analyzed in procedures #4 and #5 of the first day's activities.
Note: The ten pairs should be different from those given on the student's activity sheets as the demonstrations will act as examples for the students to follow.

a) Sodium + Iodine
b) Oxygen + Oxygen
c) Chromium + Sulfur
d) Radon + Fluorine
e) Barium + Bromine
f) Hydrogen + Hydrogen
g) Indium + Chlorine
h) Carbon + Oxygen
i) Tin + Sulfur
j) Rubidium + Nitrogen

4. Gather all materials necessary for each group of students to assemble the styrofoam models of the selected compounds to be illustrated as given in procedure #6 of the second day's activities.

5. Prepare copies of the periodic table, 1 copy per student.

6. Prepare copies of the assessment worksheet / Activity Guide, 1 copy per student, from the associated file.

Procedures

Day 1 Activities

1. a) Set up multiple bond strength test apparatus in front of the class. Attach single, double, and then triple rubber bands to the apparatus and have students record on their activity sheets, the weight it took for the bands to snap.
b) Emphasize that many nonmetallic elements form multiple bonds to achieve the octet and chemical stability.
c) Review with the students that for the Group A elements, the Roman numerals above each vertical row on the periodic table give the numbers of valence electrons for all elements in that family.
d) Emphasize that the halogens of Groups VII A need only one electron added to their outer shells to achieve the octet, therefore, they form primarily single bonds; the elements of Group VI A need two electrons added to their outer shells to achieve the octet, therefore, they primarily form double bonds and the elements of Group V A need three electrons added to their outer shells to complete the octet, therefore, they will primarily form triple bonds.
e) Refer the students to the demonstration and ask them to predict which form of bond is the strongest: single, double or triple.

2. a) Write the following set of two carbon chain molecules on the board: C2H6, C2H4, C2H2.
b) Have the students look up the group numbers for both carbon and hydrogen and record them on their activity sheets then tell them to predict the numbers and types of bonds each element can form.
c) Emphasize that hydrogen does not achieve an octet, but rather, achieves stability when reaching the same outer shell configuration as that of helium (a noble gas with only two electrons in its valence shell).
d) Have the students draw out on their activity sheets the bond illustrations of the two carbon chains showing the correct numbers of bonds between the carbon atoms and between the carbon and hydrogen atoms.
e) Have the students predict which of the carbon chains illustrated above would take the most energy to break down.

3. a) Explain the concept of electronegativity to the class (it is a measure of an atom's attraction for the shared electrons within a chemical bond). Emphasize the three major periodic trends that are exhibited:
i) Electronegativity values increase left to right across the periods.
ii) Electronegativity values increase bottom to top within a group.
iii) The noble gases are not given electronegativity values, as they are chemically stable, and do not accept or transfer electrons under normal conditions.
b) Have the students predict the electronegativities of the ten elements listed on their activity sheets utilizing the locations of the given elements on the periodic table. Have the students label the elements' electronegativities as: low, moderate, high or no value assigned

4. a) Explain that there are three primary types of bonds that can be predicted on the basis of the difference in their electronegativity values: the greater the difference, the greater the ionic character.
i) Non-polar covalent bonds have little or no ionic character; show an equal sharing of electrons between the atoms; usually composed of two non-metallic elements that are situated closely together on the periodic table or composed of two atoms of the same element- the diatomic molecules.
ii) Polar covalent bonds have a significant ionic character; show unequal sharing of electrons between bonding atoms, usually composed of a transition or representative metal with the non-metals of periods 3-6.
iii) Ionic bonds have a high percentage of ionic character; there is an actual transfer of electrons from one atom to another, usually composed of a light active metal of Groups IA and IIA with the non-metals of period 2; and/or those of Groups VIAa or VIIA.
b) Have the students predict the types of bonds that will occur between each of the ten (10) pairs of elements listed on their activity sheets. The students are to use the elements' positions on the periodic table and their understanding of bond types to make their predictions as accurately as possible.

5. a) Emphasize that the lesser electronegative element forms that central atom to which the bonding atoms, the more electronegative element, connect. In all cases, each and every atom is trying to reach chemical stability by having outer shell arrangement similar to those of a noble gas. To do this, they can form single, double, or triple bonds between the central and bonding atoms based on the number of valence electrons of the bonding atom and the number needed to reach stability.
b) Have the students determine the numbers and kinds of bonds that take place between the central atoms and bonding atoms of the previous ten pairs of elements listed on the student's activity sheets.
c) Have the students draw on their activity sheets, bond diagrams for each of the compounds formed from the bonding of the ten pairs of elements above.

Day 2 Activities

6. a) Separate the class into groups of four students per lab station. Pass out the Styrofoam balls, rubber bands, toothpicks and pipe cleaners to each group.
b) Emphasize that they are to bond the styrofoam balls together by using the following set of materials to illustrate the type of bond being formed.
i) Non-polar covalent bonds use rubber bands attached to the balls by thumb tacks
ii) Polar covalent bonds use the 3 inch pipe cleaners
iii) Ionic bonds use the tooth picks
NOTE: They are to show the kinds of bonds, single, double or triple, by using the appropriate number of attachments listed above between the central and bonding atoms.
c) The students are to make 3-D molecules of each of the following nine compounds:
i) Hydrogen Gas: H2
ii) Zinc Sulfide: ZnS
iii) Potassium Nitride: K3N
iv) Ammonia: NH3
v) Calcium Oxide: CaO
vi) Oxygen Gas: O2
vii) Aluminum Iodide: AlI3
viii) Carbon Disulfide: CS2
ix) Lithium Chloride: LiCl

Assessments

The students are to show their understanding of the chemical and physical nature of bonding between atoms in the formation of compounds by noting the placement of the bonding elements on the periodic table. They should be able to predict the following five factors as illustrated by their answers to the problems listed on their activity sheets which will be submitted to the teacher for grading purposes after completion of the activity:

1) The relative electronegativity value of any given element.

2) The relative ionic character between any two elements.

3) The number and kinds of bonds that any element can form: single, double, or triple.

4) The relative strength of the bond taking place.

5) The actual type of bond taking place:

a) Non-Polar Covalent Bond

b) Polar Covalent Bond

c) Ionic Bond

Extensions

1. Prepare copies of the Periodic Table showing the known electronegativities of the elements. Have the students calculate the true electronegativity differences for all pairs of elements studied during the two days and then compare the answers to their predicted values logged on their activity sheets. Then, have them list their percent error by the formula;
% error = 30-# correct answers/30 x 100%
2. The same module can be expanded by bringing in the topics of hybridization and molecular geometry with bond illustrations to show the effects of lone electrons and shared pairs of electrons about the central atom and bonding atoms making up a compound. The students could use this information to show the true, three-dimensional molecular structures of the various compounds previously modeled.
Return to the Beacon Lesson Plan Library.