University of Virginia
Physics Department

Bonding

A Physical Science Activity

2003 Virginia SOLs

 

Objectives

Students will

 

Motivation for Learning

Driving Question

Do we always like everyone we meet? Do we like to spend time with everybody we know? Do we sometimes wish there were two of us around to make things easier? Well, elements are like people - they don't always want to hang out with each other either. Some elements really attract each other and when they get together, they make something called a compound. These compounds are like friendships - they are all relatively stable, but some are more so than others. The elements really enjoy being with each other more than they enjoy being by themselves. Every so often, however, an element in a compound sees another element they'd rather hang out with more, so compounds break up (just like friendships). When these elements get together to make a compound, we call that bonding. (We often use that word to describe people also.) When elements (and people) bond, there has to be some give and take. In some cases, one element gives and the other element takes. (Although this sounds bad, it's really quite good for the relationship.) In other cases, however, both elements share with each other.

 

Background Information

The following activities are designed to help students understand the process of bonding and the definition and properties of compounds (compared to those of elements and mixtures). As an introduction to bonding, the students will need to be introduced to the idea of valence electrons. Valence electrons are the electrons that are on the outermost energy level (shell) of the atom. These electrons are available to take part in bonding (whether they be given away, added to, or shared). When these electrons are given away, taken in, or shared, there is a chemical change taking place and the compound that is formed is somewhat different from the two original elements. The two types of bonding we'll focus on are ionic bonding (giving and taking electrons) and covalent bonding (sharing electrons). The activities may be done individually or together throughout an entire unit on bonding.

 

Student Activity

To print out the Student Copy only, click here.

Activity 1 - Valence Electrons 1

 

Materials

 

Procedure

  1. Have three students (or a suitable number for the size of your class) come to the front of the room and hand them a large number of marbles. Have them put as many of those marbles as they can in their pockets and just hold what's left over in their hands. These marbles will then represent valence electrons. Different students should have different numbers of marbles (valence electrons) which makes them different from each other.
  2. Keep these students up front and call up three more students. Give them a large number of marbles, but not enough to fill their pockets. As a little bit of a lead in to bonding, ask the class what the students up front could do to make everybody happy (so that everyone has full pockets and no one has to walk around holding marbles all day). Hopefully, they will come up with the idea that the people with extra marbles could give those to the people who don't have enough marbles.

 

 

Activity 2 - Valence Electrons II

 

Materials

 

Procedure

  1. Another way of showing valence electrons (which can become more quantitative and concrete) is adapted from an activity in Physical Science (New York, Glencoe McGraw-Hill 1995). Give each student an egg carton set up like the following drawing. (The black sections mean they are filled in or covered up so that the students cannot use them.)  

  2. Each student will receive a different number of marbles (1 - H, 2 - He, 3 - Li, 4 - Be, 8 - O, 9 - F, or 10 - Ne). Make sure that each student (except those with He and Ne) can "bond" with another student. Instruct them to place one marble in each open spot in the egg carton until they run out of marbles. They should start with the first energy level, fill that first, and move on to the second energy level.
  3. Remind them of the definition of valence electrons. Ask them first to identify which shell is the outermost in the atom (the highest one that has any electrons). Once they have identified either the first or second energy level correctly (by telling you or writing it down to have you check it), have them count the number of electrons in that level. This is the number of valence electrons they have. Ask the students to write the answers to both of these questions on a sheet of paper on their desks so that you can quickly and easily walk around the room checking answers.
  4. Ask the students to count the total number of electrons they have and identify which element they have represented and in which column on the periodic table the particular element is placed. They should also write these answers on the same piece of paper.

 

 

Activity 3 - Elements, Mixtures, and Compounds

Adapted from: Prentice Hall (1995). Exploring Physical Science Laboratory Manual

At this point, you may want to introduce the idea of a compound. Sometimes a good way to do this is to liken them to relationships (as in the driving question section). You want students to understand the difference between elements, compounds and mixtures. If you have not already done this, you may want to try a lab activity that will allow students to observe the specific properties of an element, a mixture, and a compound.

Safety note: This activity involves sulfur and often results in strong sulfur fumes being emitted. The teacher should use discretion when planning this activity; consider ventilation, student allergies, odor sensitivities, etc. It may work better to perform as a demo for students and have them actively observe before and after states of the elements.

Note to teacher: In steps 13 and 14, students will be breaking and handling broken test tubes. There are several options for altering this.

Materials

  • Safety goggles
  • Plastic bag
  • Paper (filter paper works well)
  • Test tube (or evaporating dish)
  • Balance (digital or triple-beam)
  • Test tube clamp
  • Sulfur powder
  • Bunsen burner (or heat source for a chafing dish)
  • Iron powder
  • Striker
  • Scoop
  • 250-mL beaker
  • Hand lens
  • Forceps
  • Magnet

Procedure

  1. Place a piece of paper on the balance and observe its mass. Scoop out sulfur powder onto the paper until you have added 3 g of the powder. Remove the paper and sulfur powder from the balance.
  2. Use the hand lens to help you observe properties of the sulfur (color and size and shape of the particles). Record your findings in the data table.
  3. Put the magnet inside the plastic bag (so that any particles attracted to the magnet can be easily removed). Run the magnet over the top of the sulfur powder to see if there is any interaction. If any particles are attracted to the magnet, hold the particles over the paper and carefully remove the magnet from the plastic bag so that the particles will fall back onto the paper. Record your findings in the data table.
  4. Keep the sulfur powder on the paper and place it to the side.
  5. Place a new piece of paper on the balance and scoop out 5 g of iron powder. Remove the paper and iron powder from the balance.
  6. Use the hand lens and the magnet to repeat steps 2 and 3 with the iron powder. Record all observations in the data table.
  7. Make a mixture of the two powders together on one piece of paper. Use the scoop to mix them up and make sure that the particles are evenly distributed.
  8. Repeat steps 2 and 3 for the mixture of iron and sulfur particles. Again, record observations in the data table.
  9. Put cold water in the beaker until it is about half-full and then place the beaker to the side.
  10. Carefully pour the mixture of iron and sulfur powders into the test tube. *Note-if opting to perform this as a demo for students, an evaporating dish may used. Then it may be passed around to observe after the experiment's completion.
  11. Light the Bunsen burner and make sure you get a nice flame. (Have your teacher check it if necessary.)
  12. Hold the test tube with the test-tube clamp and place it in the flame. (Make sure the mouth of the test tube is not pointed at you or anyone else.) Move the test tube around in the flame to make sure all of the contents are getting heated evenly. Continue this for approximately 2-4 minutes or until no more changes are occurring in the test tube. Noxious fumes are likely to emerge from the test tube during this sequence.
  13. Shut off the gas to the Bunsen burner and quickly place the test tube in the beaker. The cold water should cause the test tube to break. If the test tube does not break, call your teacher over and have her break it for you.
  14. Do not touch any of the pieces in the beaker. Use the forceps to pull the substance from the test tube out of the water and place it on a piece of paper.
  15. Repeat steps 2 and 3 for the compound that was made from the sulfur and iron powders. Record all observations in the data table.

 

Data Table

Physical Properties

Sulfur Powder

Iron Powder

Iron-Sulfur Mixture (prior to heating)

Iron-Sulfur Compound (after heating)

Color

 

 

 

 

Shape of particles

 

 

 

 

Size of particles

 

 

 

 

Interaction with magnet

 

 

 

 

Have a follow-up discussion about the properties observed for iron and sulfur and whether those properties were still observed when the two were in a mixture and when the two were in a compound.

 

 

Activity 4 - Ionic Bonding

 

Materials

 

Procedure

  1. When you are ready to move on to bonding, a good activity for students to represent bonding goes back to the egg cartons used earlier.
  2. Tell students that if the outermost shell of the atom they have represented is not completely full, then just like with partially filled pockets, the atom is not as "happy" or stable as it could be. The atoms will want to run around and find someone to help them out and make them more stable. Remind them that it's O.K. to have less marbles (or electrons) than you started with. As long as the outermost energy level is full, the atom is stable (and happy).
  3. Have the students decide what needs to happen to their atom in order to make it stable. Do they need to give away 3 electrons or gain 5? (As in boron) Do they need to give away 6 electrons or gain 2? (As in oxygen) Do they not need to do anything? Ask them which would be easier to do (less moving of electrons) - giving away 3 or gaining 5? Hopefully they will realize that they want to do whichever action means moving fewer electrons. Once they have decided what needs to happen to their atoms, they should walk around the room looking at each other's atoms to find the person with whom they can partner up.
  4. Once the students find their partners, they should bring their atoms together and make the electron switch in order to make both atoms stable, and then they should stick together as a pair.  

  5. The two students should look on the periodic table and find each other's elements and identify the column to which they belong. The students should then write down (on the same piece of paper which they've been keeping all the other information) which element they are partnered with and the column that it's in.
  6. Call the whole class back together for a discussion (but keep pairs of students together). Have each pair of students show where their elements are on the periodic table. Hopefully, once all the pairs have gone, the students will begin to see a pattern (that the far right column doesn't combine with another, that the 1st column mixes with the next to last column, etc.) Now would be time to define this type of bonding. Ionic bonding happens when electrons are given away and taken in, and it generally takes place with an element from the left side of the periodic table (a metal) and an element from the right side of the periodic table (a non-metal).
  7. You could also introduce the idea of writing formulas for compounds here. The students figured out which element they had represented and which element they could bond with, so it is just a matter of putting together the symbols to write the formula. For example, if one student had lithium and they bonded with a student that had fluorine, they would have found the symbols from the periodic table to be Li and F. Since there's only one of each, the formula is written as LiF.

 

 

Activity 5 - Covalent Bonding

 

Materials

At this point students are only working with elements in the first two periods, so they will be limited to the numbers of compounds they can make. These few examples, however, will help students visualize and manipulate objects to better understand the idea of a covalent bond. The examples we can do easily are the diatomic elements nitrogen, oxygen, and fluorine. This exercise will be difficult for students to discover on their own, so you should have every student in the class work on the same element while you talk them through the procedure.

 

Procedure

  1. Start with fluorine, as it's the easiest to bond with only one shared pair.
  2. Have each student represent a fluorine atom with his or her egg cartons and marbles. Have students pair up so that they have two atoms with them.
  3. Ask them to remember the activity with ionic bonding and ask if there's any way to give and take electrons so that both atoms are stable. Hopefully, they will realize that they can't do that. Since these atoms can't give and take electrons to make themselves stable, they are going to have to share the electrons.
  4. Have each student pull out the very last marble from the carton and hold on to it. Have them overlap (stack) the last row of their egg cartons together and place the two marbles they have in their hands into the two empty spots. This represents the shared electron pair, and the cartons are actually "bonded" together.  

     

  5. Now the students can write the formula for the compound they made. Tell them that since they have two of the same atom, we have to show that there are two of them, so we write it as F2.
  6. Follow the same procedure for Oxygen and Nitrogen. These are bonded with a double bond (two shared pairs) and a triple bond (three shared pairs). So in these cases the students will have to overlap the last two (or last three) rows of their egg cartons and share the marbles accordingly.

 

 

Extensions

  1. Attach several egg cartons together or get a larger container to include higher energy levels. Have students represent the higher number elements with marbles and determine the number of valence electrons. Have the students identify the elements on the periodic table and the column in which the element is placed. Have the students compare these with the lower number elements in order to see that all elements (at least those in the main groups) in the same column have the same number of valence electrons. Discuss the correlation between number of valence electrons and properties of elements.
  2. Expand this exercise so the relationship between elements in the compound is no longer one-to-one. For example, have one student with the egg carton representing beryllium and two students with their egg cartons representing chlorine. Show how both chlorines get one electron from beryllium so that all three atoms are more stable.

 

Students with Special Needs

Each student should be able to participate in this activity. If a student has difficulty manipulating the marbles, you might pair that student up with someone else who can put the marbles in the place where the first student tells him.

Click here for further information on laboratories with students with special needs.

 

Assessment

  1. Have students write down the answers to the questions you pose during the activity (for immediate feedback and correction).
  2. Give students an element and have them represent the electrons with the egg carton and marbles. Then they can state the number of valence electrons and determine what needs to happen to the atom in order to make it more stable. They could then pick the element with which it would most likely combine.