This week was another full and busy week of AP chem. We took a big test on Lewis structures and then worked for the rest of the week on ionic bonding. A little side note: our class took an actual AP Chemistry multiple choice exam and this was a very difficult test for all of my class.

            The first half of this week we spent on reviewing for testing and actual testing. We spent Monday on reviewing Lewis structures, polarity, hybridization, and VSEPR Theory. All of this led up to a huge test the following day. The test was a very comprehensive one and was a good challenge. I found the test to require quite a bit of knowledge on the materials that we learned but I felt pretty confident taking it. On Wednesday we took an AP Chemistry multiple choice exam which was pretty difficult. It was definitely quite difficult for me as a I only got 13 questions out of 60 right. To reflect on this, it made me very nervous for the ap exam. I hope at the end of the year I am able to easily do well on this multiple choice exam.

            The last two days of this week we spent on doing a couple intro lessons to ionic bonding and metals. The basis for an ionic bond is a bonding between a cation and an anion. We can see that the formula will always have to be a balance between the negative and positive charges of two atoms. Ionic compounds will always be made up of a metal and nonmetal. Unlike covalent bonds, there is no sharing of electrons in ionic bonds. However, there is a strong attraction between the two ions due to the Coulombic force. Usually in an ionic compound there will be a negative charge on the metal and a positive charge on the nonmetal. The charges are generally determined by the group that the element is found in with exceptions for the transition metals. To reflect on this topic I thought it was very simple, it was a little hard to follow along at times during this lesson but I understood basically everything.

            We also learned about some properties of ionic bonds. We discovered that melting point can also be a representation of how strong the bond between the two atoms is. The higher the melting point, the stronger the bonds will be between the two atoms of an ionic bond. On Friday we spent a little bit of time on metals too. We learned about some of their properties and what alloys are. Alloys can be defined as a solution that has the properties and characteristics of a metal. To reflect on our work with metals I thought it was quite easy, although the concepts are likely to get much more complicated throughout the course of this unit.

            That's basically what we did this week. To reflect I thought it was a difficult week because I was very busy with soccer every single day. This made it very hard to find time to review for the test, although I felt very confident about it. I was extremely surprised that I didn't do better on the test and I really wish the tests were passed back in class so I can see my mistakes. Other than that I thought it was a good week of AP chem, my understanding of the new material was about a 9, and I participated in class activities well every day.

Example of an alloy

This week we had a lot going on in class. We did many different activities to help us better our understanding of the VSEPR theory and how molecular and electron domain geometries work.

            For the first half of this week, we worked online building our models that we had already learned about from our balloon and gum drop lab. We created a molecular orbital to represent our molecule and we could use this orbital to find out a lot of information. We looked at the dipole moments that occurred in the molecule and the individual dipole bonds that were present. From this we could see the partial charges in atom and could even better understand the partial charges in the molecule by looking at the electrostatic potential map. Atoms in the molecule that were the most electronegative appeared red on the map and the atoms that were least electronegative appeared as a cool color, either blue or green. We could also see the bond angles that were present in the geometries even though we already knew this from the worksheets and lectures that we had done previously.

            We found out from this lab that the unpaired electrons on the central atom are electron clouds that push down on the bonds of the molecule and reduce their angles and this is why they sometimes deviate away from their standard value.

            We also talked a little bit about pi and sigma bonds this week. Pi bonds occur when there is an overlap of the p orbitals while sigma bonds occur when there is an overlap of the s orbitals or sp orbitals. This concept was a little complex at first to understand but made more sense to me when I understood that sigma bonds occur in all bonds while pi bonds occur in bond orders that are higher than one (i.e.: a double or triple bond). For a double bond there is one pi bond and one sigma bond while for a triple bond there are two pi bonds and one sigma bond.

          The last thing we talked about this week is hybridization. This has to do with the amount of bonds and unshared pairs of electrons around the central atom in a lewis structure. For example if there are 2 bonds the hybridization is sp, if there are 3 it is sp2, and so on. Eventually you need to start using the d orbital. To reflect on this topic I thought it was quite easy and simple to understand, all you have to do is be able to count.

          To reflect on the entire week I thought I had a very good understanding and I participated well. At first I didnt really understand much of what was going on with bonding. This weekend I really spent an extremely long time working on chemistry and doing the quizzes online and now I feel extremely comfortable with the material. I now feel like I am a 9 on a scale of understanding the material. I am very happy because I was extremely anxious last week that I would not do well on this test, but now I am very comfortable with the stuff we've learned.

Here is a twenty minute video further explaining VSEPR theory: http://www.youtube.com/watch?v=nxebQZUVvTg

This week in AP Chem we worked a ton more on Lewis structures. We specifically zoned in on expanded octets in Lewis structures and also which Lewis structures is more correct. We spent some time with pogils and also did some practice problems to further our knowledge. To reflect on these pogils, I thought they were very helpful in allowing me to understand topics that were very confusing at times.

            Up to this point, we knew that there was a certain checklist needed for making Lewis structures. First, you must determine, from the compound, which atom is the least electronegative and place this atom as the center atom. This first step is extremely important and must be done correctly or else your lewis structure will be wrong. You choose the least electronegative atom as your center atom because you want this atom to be the least likely to take away electrons from atoms and be the most likely to share electrons with other atoms. Next, you must create bonds with the pairs from the outside electrons and the inside atom and complete the octets for each atom. ( Hydrogen has a complete octet with two electrons.) We then want to place any remaining unpaired electrons around the inside atom. This checklist is important because drawing a correct lewis structure is the basis for more complicated problems.

            This week we spent time going over what we learned on formal charges in a lecture last week. Formal charges can be defined as the number of valence electrons an atom as minus the bonds it has attached to it minus the number of unbonded electron pairs surrounding the atom. With the pogil we did we were able to determine that the most correct Lewis structure is the one that has the least formal charges, preferably a overall formal charge of zero on the compound. We learned that for certain atoms like oxygen you can have the formal charges memorized. If there is only bond attached to oxygen, it has a formal charge of -1. If there are two bonds attached to oxygen there is a formal charge of 0. If there are three bonds attached to oxygen, there is a formal charge of +1. There are many other atoms like oxygen which we need to have their formal charges based on number of bonds attached to them memorized. To reflect on our review of formal structures, I thought the pogil was very helpful. Formal charges are rather easy for me but sometimes it can be difficult to determine the most correct lewis structure based on the formal charge.

            We also completed another pogil regarding expanded octets. We learned that elements in the third period or lower can have extra pairs of electrons placed around them that can be more than a complete octet. This is because elements in the third period or lower have access to the d-orbital. To reflect on this pogil, it was kind of a difficult difficult concept to understand, but I think in the end after completing the pogil and asking a lot of questions I have it down pretty well.

             To reflect on this entire week in AP chemistry, it was a tough week filled with new and complicated concepts, but for the most part I understood everything. I do not really have any new questions about this week and I feel that I participated very well with my table and in class. I definitely still need to work more on how to draw lewis structures correctly before the upcoming test.

 This week was a lab week in AP Chemistry. We finished our data collection part of the lab on finding the mass of copper in a brass solution. We also worked on a few pogils to extend our knowledge about Lewis structures. We completed a pogil that had to do with bond order and bond strength, another one regarding  resonance and a third one on VSEPR theory. We learned an extensive amount of new ideas and concepts from these pogils that will likely be very important to us as the unit went on. To reflect on these pogils, I thought they were very helpful in allowing me to grasp new and difficult ideas.

            The first pogil we worked on was one that had to do with two main ideas, bond order and bond strength. Bond order occurs when you require many bonds to connect two atoms’ valence electrons together so that they are able to share electrons. A higher bond order will mean that more energy is needed to take apart this bond. A lower bond order means that it will take less energy to take apart the bond. We were able to understand this from working on the pogil on bond orders. To reflect on this pogil, I think it was quite helpful in helping us learn about bond order and bond strength. These are two important ideas that we will probably be using later in the trimester.

            In our next pogil we took a look at resonance in Lewis structures. We had already learned what those were about from the lecture quiz that we worked on last week. Resonance is when you can multiple Lewis structures from the bonding of the same atoms based on using different bond orders on different atoms. Another very important main concept that we learned from this pogil is that as bond order increases, bond length decreases. To reflect on this pogil, it was also very helpful and allowed me to understand the basic principles of resonance in Lewis structures 

            In the last pogil we did for this week, we worked on VSEPR theory. This theory shows us the overall shapes of molecules. We finished this pogil by creating a Lewis structure for an atom and then building a balloon model of that atom using the surrounding atoms and unbonded electron pairs as balloons. The central atom was in the center and not needed to be represented by balloons. This pogil helped show us what a compound will truly look like when it is bonded. To reflect on this pogil, I found VSEPR theory to be quite hard and complicated, but the pogil helped me a lot.

Diagram showing the VSEPR theory

           This week we also took part in a lab. We completed our data collection part of the lab. Our question which we are testing is what is the relationship between absorbance and concentration of Cu in a brass solution. Although I was not in class for the first day of the lab, I came back the second day and got down the data and had the lab described to me by one of my partners. We tested the relationship between absorbance and concentration by breaking down a brass screw in nitric acid to get it down to only Cu. We then took our absorbency data and will spend next week analyzing this data. To reflect on this lab, I thought it was pretty interesting and fun, I'm excited to do the lab report.

            I thought I had an alright grasp of the material that we worked with this week. I didn’t find it too complicated, but some of the ideas were difficult to understand, and i am still foggy on some topics. My participation in all of our work was 100% besides the day I was not in class. I don’t have any questions about anything we went over this week and I have seen that I still need to work on getting better at preparing for labs better, by coming up with better beginning questions.