Ms. Zbrozek

Biology I   

2^nd period

6/13/08

50 minutes

Objectives:

--The student will construct models of molecules to depict several bonding diagrams that demonstrate knowledge of both ionic and covalent bonds.  (Science 6a, DOK II)

Materials:

Whiteboard, whiteboard markers, paper, writing utensils, gumdrop worksheet, bag of gumdrops and toothpicks.

Bell work:

--Move your desk next to a partner. 

--You have 7 pennies on your desk.  Your partner also has 7 pennies on their desk.

--How can you and your partner use the pennies on your desks so that both of you have eight pennies?

--Write down your ideas on a piece of paper. 

--Also, get out your periodic tables and set them on the side of your desk.

(3 minutes)

Set: 

I want you to think of a time when someone gave you something and it helped both of you. Next, I want you to think of a time when someone (or you) shared something with someone and both of you benefited from it. Listen to their examples and talk about them. Today we will be talking about these relationships, only we will be talking about atoms of each element giving and sharing—which is one way that an atom can bond.  By the end of today you will be able to draw out the relationships of the two main types of bonding between atoms, using the atom structure we talked about yesterday.  (4 minutes)

Procedure:

Make an overhead of the bold words and sample problems.

1. TTW have a picture of a chlorine atom drawn on the board.  Remind the students that atoms do not work by themselves, but they join together to make molecules and compounds.  Ask the students to review what a molecule and a compound are. 

2.   TTW write H2O on the board.  Ask the students why they think that we don’t draw it as HO2….hopefully, this will lead them to say that there are two H’s and one O, not one H and 2 O’s.  Ask them why not?  Bring up the idea of rules, lead them to understand that there are specific rules that tell which atoms bond together.

3.   TTW discuss the chlorine atom on the board.  Ask the students to count how many electrons are on the atom.  Then ask the students to find chlorine on their periodic tables.  Point out that the 17 found on the table is called the atomic number, and that tells how many protons there are.  For a neutral atom, there are the same number of protons and electrons….17 +1 charges and 17 -1 charges balance out.  Ask the students why there are three rings of electrons drawn….look for the answer that the electrons are in different energy levels. 

4.  TTW continue discussion.  The outer layer is the most important…just like you look at an apple and the outside tells you the properties of the apple—whether its red or green, whether its ripe, whether its bug bitten or good to eat—the outer electron layer of that atom will tell you some properties—like if it wants to react or not.

5.   Atoms are stable if their energy levels are full, which means that there are eight electrons (two in the first shell).  But usually these levels are usually not full.  So, they tend to react or combine with other atoms in order to become stable….just like when a kid wants a new toy…they are going to work to get the toy they don’t have to make them happy, just like the atom that does not have a full shell will work to get a full shell to make them happy.  When we look at this chlorine atom, how many electrons do we see in the valence shell?  (seven)  Does it want to react or not?   (yes)  (7 minutes= 14 total)

5. Right, so when atoms want to become stable, they can react in two ways. One way is through sharing electrons. (Relate back to set examples). This is referred to as a covalent bond. Give an example of a covalent bond using Cl2…two chlorine atoms bonded together.  When we draw a line between the atoms, that shows the bond.  Covalent=sharing.  We can see that each chlorine has seven electrons in their valence shell, but they each want eight.  If they share, they will all be happy.  This is just like at the beginning of the hour with the pennies.   

7. Now lets talk about another type of bond. In this scenario, one atom is giving and the other is receiving, but both are benefiting. Take for example sodium and chlorine. Look up and draw sodium and chloride. Draw on board and ask if they are stable. NO they are not. But do they want to share their electrons to be happy? NO. What is one way both atoms would benefit? Exactly. Sodium would “give” away one electron to Chlorine. 8. This sort of bond is called an ionic bond. The name ion refers to the electrical charge of an atom (in this case, sodium and chlorine). If an atom gives away an electron it becomes a positively charged ion, if an atom receives an electron it becomes negatively charged. Now, who has heard of the phrase opposites attract? The case is no different here. The sodium and chlorine atoms now have different charges and they are attracted to each other.  Together they form sodium chloride, or table salt.   10 minutes=25 total.

8.  Pass out the gumdrop worksheet, and a bag of gumdrops and toothpicks to each student.  TTW work through the first two examples (one ionic and one covalent) and then aide the students as they work through the next examples.  (22 minutes)

Closure:

You guys did a really good job of building the models and showing ionic and covalent bonds.  What does a covalent bond mean?  (sharing)  What does an ionic bond mean (transfer).  Remember that usually, ionic bonds are made with two elements on opposite sides of the periodic table. 

For the rest of class time today, we’ll have a review session and then an exam that will cover what we’ve learned this week.  (3 minutes)

Assessment/Evaluation:

Objective: --The student will construct models of molecules to depict several bonding diagrams that demonstrate knowledge of both ionic and covalent bonds.  (Science 6a, DOK II)

         Informal:  TTW observe as students build their models and fill out their worksheets to identify covalent and ionic bonds.

            Formal:  TTW include the material learned today on the weekly exam.

 Create your own educational wiki!HelpPublic, not yet premium Privacy Policy RSS