Mighty Molecule Building

Introduction:

Most atoms are unstable by themselves and so they bond with other atoms in order to get stable. These bonds are often formed when the atoms share electrons with each other.  When atoms bond with one another they form compounds and molecules. Each different type of atom (element) has to form a certain number of bonds to get stable.

Of the 92 natural elements, only about 25% are important to living things and only four elements make up about 95% of living things.  If we can determine how those four elements bond in order to get stable, then we can understand a great deal about the chemistry of living critters. 

National Science Standard: Unifying Concept

Nature is constantly changing but there are many repeating patterns.

Georgia Performance Standards:

Students will exhibit curiosity, honesty, openness and skepticism S(K-5)CS1

Describe materials, what they are made of, and how they change. SKP1, S2P1,S5P2

Materials: One molecule set per group of students.

Exploration:

At the start of this exploration, remind students of the classroom rules that govern proper behavior when they’re combined together in the classroom.  After briefly discussing a few of these, announce that today they were going to investigate some of the patterns that atoms follow when they are combined together. Explain that, while elements and the atoms that make them up don’t abide by the same set of rules, they do follow arrangements that that students can understand.  Two of the important patterns are summarized as follows:

1) Most atoms prefer not to be (are unstable) by themselves and so they bond with other atoms in ways that make them more stable.

2) Each different type of atom (element) has to form a certain number of bonds to get stable.

Explain that when atoms bond with one another, they form substances that we call compounds and molecules. As a visual example, take one red and two yellow wooden balls and show how they represent one oxygen atom and two hydrogen atoms.  Connect  both hydrogen atoms to the oxygen atom and illustrate how they bond together to form a molecule that they all use everyday. Ask them to identify this very important molecule (water).  Carefully reveal that the yellow Hydrogen atoms have one hole in them, representing their need to form one bond in order to become stable. In contrast, the red Oxygen atom have two holes it them indicating it’s need to form two bonds. Using the sticks to represent the bonds between atoms students can easily see the number of bonds that each atom needed to gain stability.  

 Mention to the students that since there are a total of 92 natural occurring elements on the earth (show a periodic table if you have it), elements can combine together in ways that could form an almost limitless combination of compounds.  Fortunately, we can simplify things greatly by focusing our initial efforts on the chemistry of living things. As it turns out, the chemistry of life is remarkably simple (and complex). Of the 92 naturally occurring elements, only about 25 % of them are important to living things and only four elements (carbon, nitrogen, oxygen, and hydrogen) make up 95 % of all living things.  If students can understand how these fabulous four elements bond in order to get stable, then they can comprehend a great deal about the chemistry of all living things.

The Fabulous Four

Briefly use the models to demonstrate how each of the fabulous four needed to bond to gain stability.  Tell them that atoms can form one bond (single) between two atoms, or two bonds (double) and sometimes even three bonds (triple). They can also bond with another atom of the same kind. To determine how many of each atom you need to make a molecule, look closely at the chemical formula and the numbers that go with each element. As an example, show how the the formula H20 can be used to show that water is a combination of 2 hydrogen atoms and one oxygen atom.

Declare to the students that they are now ready to build some of the most important molecules on our planet.   Remember, in order for the molecule to be stable, it must form the proper number of bonds.   When you build the molecules, use sticks or springs to represent the bonds. You can form one bond (single) between two atoms or two bonds (double) and sometimes even three bonds (triple). In these cases, you need to use the springs to show the bonds because they can bend. If you have any empty holes left in any of the atoms, then the molecule will not be stable.

Procedure:   Student Activity Sheet

Build the following molecules using the ball and stick models. You may need to take some apart as you go in order to build new ones.

Congratulations, you just built some of the coolest molecules on the planet and you made sure that every atom in each one of them was stable.  By forming the correct number of bonds with other atoms, you can be confident that each of them is now a happy atom.

Guiding Questions: 

1. Do all the molecules contain only single bonds?  Why do you think this is the case?

2. Do all the molecules have the same shape? Why do you think this is the case?

3.  Because carbon (black) is the only element that can form long chains by bonding to itself over and over, it is the backbone element of all living things. What is unique about carbon that allows it form these big chains?

4. Three of the molecules (methane, propane and wood alcohol) that you made are used by people to as a fuel (for energy) What do each of these molecules have in common? 

Explanation:

Concept Discussion:  

Molecular  models are  a great way to introduce basic concepts regarding how atoms combine with one another. Students can appreciate that, like us, atoms are often unstable by themselves and so it would make sense that they bond with one another in order to improve their stability. Because atoms differ in structure each has to form a certain number of bonds in order to get stable (usually 1-4 bonds). Although there are many elements, just four elements make up the vast majority the substance in living things. If students can use trial and error to determine how these elements can bond with one another, they can begin to grasp some key concepts that will improve their understanding of living things. For example, since carbon must form a total of four bonds in order to get stable, there are hundreds of ways that it can bond with itself or atoms. Because of this unique ability carbon is the backbone element of all living things.  Remind your students that the the sticks and springs only represent the bonds (attractive forces) that keep the atoms together. You can form one bond (single) between two atoms or two bonds (double) and sometimes even three bonds (triple).  If you have any empty holes left in any of the atoms, then the molecule will not be stable.  Students will invariably come up to you with dozens of different "homemade" molecules to ask if they are real. If all the holes are filled and all atoms are "stable" then an appropriate response is "probably".

Teacher Notes:

Simple Molecular model kits can be purchased at www.flinnsci.com  For elementary students, the larger 1 inch diameter balls are recommended.