AP Chem Test, Mole Day, and Ionic Bonding

On Tuesday we took our second AP Chem test on VSEPR and Bonding. We spent Monday reviewing for the test. We reviewed about the different shapes included in VSEPR and we talked about their angles. We also discussed resonance structures and formal charges. Another thing that some people did to prepare for the test was to redo the bonding taskchain that was homework for over the weekend. The taskchain included problems about domain geometry, types of bonding, and electron structure of compounds.

Overall the average score for the multiple choice was 83.9% and the spread of scores looked like this:

Overall the average score for the free response was 88.3% and the spread of the scores looked like this:

I didn't do so great on the free response. This could have been because I didn't review the task chains the night before. It could also be that I didn't understand how to explain all of the concepts correctly and I should have asked more questions about this before the testing day.

On Wednesday it was 10/23 which is mole day. We ate mole cookies and drank hot chocolate to celebrate the most important number in chemistry, Avogadro's Number  6.02 x 10 ^23. We also listened to a song about moles and mole day and were told some mole play-on words and puns.

 

Here is a parody of "Call Me Maybe" by Carly Rae Jepsen its called "Mole Day Baby". I've got to give these chemistry teachers some props they were pretty cool in this video!

 

On Wednesday we were also introduced to hydrogen bonding through an article from the magazine Chem Matters. This article talked about paint ball and how hydrogen bonds are used in the paint that is used in paintball because it makes it washable. From this article we learned that hydrogen bonds form in atoms that have a large difference in electronegativity with hydrogen. The central atoms of these molecules have lone pairs of electrons that can attract other the hydrogens of other molecules. This forms a hydrogen bond which is the strongest intermolecular force. These bonds are usually formed with Oxygen, Fluorine, or Nitrogen and Hydrogen. In order to practice our science writing skills we wrote essays about this article and how it related to the rest of chemistry. This was helpful in two ways. First it helped me to practice my writing about science topics and it also made sure that I understood the reading and the concept of hydrogen bonding.

At the end of the week we started to move away from covalent compounds and bonding and into ionic compounds and bonding. We started a POGIL on ionic bonds on Thursday and finished it up in class on Friday. We reviewed that metals form cations and nonmetals form anions. Cations are positively charged because they lose electrons to be more like the closest noble gas. They are smaller than a neutral atom of the same element because they lose their outer valance shell of electrons. Anions on the other had are negatively charged because it is easier for these atoms to gain electrons to have the same number of valance electrons as the nearest noble gas. These ions are larger than a neutral atom of the same element. This is because the electrons have more repulsion away from each other and this makes the ion larger. 

Overall this week I think I learned a lot. I learned that I need to prepare for the tests differently. I'm going to talk to my friends who did better and see what kinds of strategies they used for studying for the test. 

 I also reviewed the material about ionic bonding that was covered last year and during the summer. I think that I would give my understanding of the material a 9/10. I think because we learned about ionic bonding last year I understand it well. I gave a 9 and not a 10 because we still have things to learn about metals in order to understand ionic bonding.

WebMO building, Hybridization, Domain Geometry Names, Polarity, Bond Types

This week we expanded our knowledge about electron and molecular domain geometries by applying the different shapes to models that we built on the computer. We learned how to tell what shape the molecular domain geometry would be by looking at the electron domain geometry. Some of the more confusing geometries were the ones that follow:

This shape is called bent (trigonal planar). It is created from a trigonal planar shape that has 1 lone pair of electrons.

This shape is called trigonal pyramidal. It is created from a tetrahedral shape that has 1 lone pair of electrons.

This shape is called bent (tetrahedral). It is created from a tetrahedral shape that has 2 lone pairs of electrons.

 This shape is called seesaw. It is created from a trigonal bipyramidal shape that has 1 lone pair of electrons.

 This shape is called T-shaped. It is created from a trigonal bipyramidal shape that has 2 lone pairs of electrons.

 This shape is called linear. It is created from a trigonal bipyramidal shape that has 3 lone pairs of electrons.

This shape is called square pyramidal. It is created from an octahedral shape that has 1 lone pair of electrons.

This shape is called square planar. It is created from an octahedreal shape that has 2 lone pairs of electrons.


We used a program called WebMO to build the structures of 13 molecules given to us. We built their molecular structure and then looked at their electrostatic potential maps to see the partial charge if any on the different parts of the molecule. The ball and stick models and electrostatic potential maps can be seen below.

We also talked about hybridization this week. We learned that if a molecule has linear electron domain geometry it will have sp hybridization. We learned that if a molecule has trigonal planar electron domain geometry it will have sp2 hybridization. We also learned that if a molecule has tetrahedral electron domain geometry it will have sp3 hybridization. After tetrahedral, hybridization is not used.


Polarity can be useful in determining what type of bond two elements have with each other. It can be determined by looking a a periodic table that has the electronegativities on it and finding the difference of electronegativity between the two atoms. It is important to know that:

• A difference of 0.0-0.4 indicates the presence of Nonpolar Covalent Bonds 

• A difference of 0.4-1.0 indicates the presence of Moderately Covalent Bonds 

 

• A difference of 1.0-2.0 indicates the presence of Very Polar Covalent Bonds 

 

• A difference of >2.0 indicates the presence of Ionic Bonds

This week we also talked about Sigma and Pi bonds. A sigma bond is a bond that has a bond order of one. A sigma bond can only be a single bond. To make a double bond 1 sigma + 1 pi bond are used. To make a triple bond 1 sigma + 2 pi bonds are used. Sigma bonds form where there is head to head overlap of orbitals. Pi bonds form where there is side to side over lap of orbitals.

Sigma Bond

 Pi Bond

Overall I feel like the WebMO and VSEPR lab report helped me to put all of the ideas of this unit together  and understand how they all are connected. This week I would give my understanding of the material a 8/10. This is because I still have some questions about certain situations but for the most part I understand the material. What helped me to understand the shapes was using my Princeton Review AP Chem Test Book. It has nice diagrams and I was able to bookmark and highlight things in it. I also think that the long discussion that we had on Friday about polarity, bonding and hybridization was also very helpful.

Resonance Structures, Formal Charge, VSEPR

This week we continued to study VSEPR, resonance structures, and formal charge.

First we finished up our VSEPR balloon and gumdrop lab. Each group presented about the different molecules that they modeled and we filled out the chart in the VSEPR Theory Lab packet. Since the gumdrop models represent the molecular domain geometry, some of the molecules had structures that differed from the balloon electron domain models. This is because when creating the molecular domain structures non-bonding pairs of electrons are not included in the model. We also learned that these non-bonding electrons can cause the angle between the central atom and the other atoms to be less than the angle expected, because they push down on the bonds. Another thing that we learned about through this investigation was how to write molecular class.

Writing Molecular class:
-Write A as the central atom 
-Write B to represent bonded atoms, use subscripts if more than 1.
-Write E for lone pair electrons, use subscripts if more than 1.

 

Next we talked about Lewis structures and formal charge. We did POGIL 16 to learn more about creating Lewis structures and how to decided which structure is more correct. We learned that the element with the lowest formal charge is the structure that is more correct. To figure out the formal charge you subtract the number of lone pair electrons and the number of bonds from the number of valence electrons of the element. You write a + or - inside of a circle for +1 or -1 and for other numbers you write them inside the circle too. If there is 0 charge then nothing is written. 

FC= (# of valence electrons that the element has) - (number of non-bonding electrons)- (number of bonds)

We learned that in some cases atoms could have a charge that canceled with another atom's charge to create a neutral molecule with a formal charge of 0. In order to determine if the structure is the best structure you must make sure to find the charges of all of the atoms. This technique can be used to determine what resonance structure is more likely to occur in nature. 


 Another thing that we discussed this week was expanded octets and how to draw Lewis structures that have a formal charge of 0.We did POGIL 17 to learn more about hypervalency and formal charge. We learned that in order to have a formal charge of 0, double or triple bonds may have to be formed. We also learned how to find the bond order in more complex molecules. 

 

 At the end of the week, we did a white boarding activity that tied all of the ideas of the week together. In this activity we worked with our table groups to determine the Lewis structure,  molecular class, electron domain geometry, molecular domain geometry, and the angles of the bonds for different molecules. We did this for I3-,  BSF, NSF, SCN-, SO2, and GeS2.

Over all this week I think my understanding of the material improved each day. I felt that the white board activity on Friday helped me to put all of the information together and know how it all relates . I enjoyed working with my group and I think that we all gained a better understanding of the material through out that class period. For me personally I would give my understanding of the material a 8.5/10. This is because I feel that I have a good understanding of the material, but I feel that I need to do more practice since I just recently figured out how it all is related. 

Copper in Brass Lab, Bond Order & Strength, and VESPR

This week in class we talked about a lab dealing with the amount of copper in a brass screw. We learned that the copper can be dissolved using nitric acid. We created an equation to find the mL of the acid that would be able to dissolve a screw that was 100% copper. This insures that there is definitely enough acid to dissolve the copper.

This is the Chemical reaction:

We came up with this equation:

  We then created and executed a procedure to find the absorbance of the Cu solution created in the reaction. To do this we created a calibration curve for a standard solution of Cu. We then created 4 other dilutions of the standard solution and took a reading of their absorbance in order to plot a calibration curve. The dilutions used were  1/2, 1/4, 1/8, and 1/16. We also took a reading of the absorbance of our reaction solution.

Another way that we compared our reaction solution to the standard solution is by the visual comparison test. This is a test where the colors of the two solutions are compared together over a white piece of paper. If the standard solution is darker than the reaction solution, a small amount of the standard solution can be taken out until it is the same color as the reaction solution. The equation to calculate this is:

(Molarity1) (Depth1) = (Molarity 2) (Depth 2)

The next thing that we talked about this week was bond order and bond strength. We did a few POGILs that will be listed below:

Bond Order and Bond Strength

Lewis Structures (II)

These POGILs helped us to understand basic concepts of bond strength and bond order. This includes learning that double bonds are stronger than single bonds and triple bonds are stronger than single and double bonds. The stronger the bond, the more energy needed to break it.

We also learned about electron deficiency and hypervalancy:

There are two elements that have electron deficiency. B is full when it has 6 electrons and Be is full when it has 4 electrons.

Hypervalancy is when a central atom in a molecule has more than an octet. This can happen with all elements that are in the 3rd period or higher because of the d block.

Later in the week we talked about formal charge. We learned that formal charge can be calculated for each element by using the following equation:

Formal Charge= # Valance Electrons -[# bonds + # nonbonded electrons]

-# of valance electrons: count the # as you have been doing
-# of bonds: the total number of bonds to the atom in question
-# of unshared elections: total # of unshared electrons around the atom in question

The last thing that we talked about was VSEPR Theory. VSEPR stands for valance shell electron pair repulsion. We learned that the shape of molecules are determined by the valance electron pairs.We baldid the VSEPR Theory Lab which investigated the idea of taking the Lewis structures and creating a 3D model of the central atom's bonds. For this activity we created the model from balloons.

Over all I thought that I understood the information from this week pretty well. I would give my understanding a 7/10. This is because I understand the basic concepts of bond order, bond length and VSEPR. I also still don't understand how to do all problems that deal with bond order because I find that it is hard to understand. I'm also still trying to grasp the formal charge and how that effects the shape of the molecules. Besides those two things I think that I'm understanding the material.