1/13-1/17

            This week in class we did a comprehensive review of all things gasses and did some demonstrations with liquid nitrogen. We did a lot of whiteboarding of problems involving ideal gases and real gases. The difference between the two can be taken into account by properties of gases and IMF’s and are seen in effect with Van der Waal’s equation.

            The bulk of the week was spent working on problems from the Gases I and Gases II worksheets. The Gases I worksheet had a lot to do with problems that involved the ideal gas equation. This is PV=nRT. We can manipulate this equation to solve for any one of the four variables that can affect gases. An ideal gas is not something we actually see in real action but is just a hypothetical gas whose pressure, volume, and temperature can be described by this equation.  We also discussed a little bit the effects of STP and what it is exactly. STP is the standard temperature and pressure conditions of gases at 0° C and 1 atm. The volume of STP conditions is 22.4 L. We also faced some problems where P, V, and T all changed for a constant number of moles. When this happens we can set up an equation where P₁V₁/T₁=P₂V₂/T₂. This equation is very helpful for finding a final variable if we know all the initial variable’s and two of the final variables or vice versa for finding an initial variable.

            We also looked at some further applications of the ideal gas law. This involved density and molar mass. Since D=M/V we can substitute in variables for volume if we need to do so. We also know that molar mass is equal to mass per one mole of substance. We can use this knowledge to rework our ideal gas equation to solve for molar mass and density of gases.

            We also touched on effusion and diffusion. Effusion is the escape of molecules through a tiny hole into an evacuated space. Diffusion is the spread of one substance throughout a space or throughout a second substance. There is an equation that is the same for both effusion and diffusion. We can use this equation to help solve for the identity of a gas based on its molar mass.

            The last matter that we discussed was the deviation of real gases from ideal gases. This can be recognized by Van der Waal’s equation that corrects the ideal gas equation due to the finite volume occupied by the actual gas molecules and for the attractive forces that are present between gas molecules. This basically raises the pressure and lowers the volume.

Here is a video of methane bubbles in my hand being ignited

            I think this has been by far one of the hardest units that we have encountered yet. The material is pretty challenging and the concepts are hard to comprehend. It requires a lot more thinking about what is really going on than just plugging in numbers into the equation. I think the whiteboarding technique has really benefitted this unit because it allowed me to see all of the work for the problems we did and understand the concepts a little bit better. Participating in the liquid nitrogen lab was also very fun and educational. Overall this was a very full week. A lot happened and a lot was covered and that will only make this upcoming test all the more difficult. 

12/9-12/13

            This tri in AP Chemistry we have been covering the topic of Thermodynamics. This topic covers both enthalpy and entropy. We spent lots of time in class doing worksheets and using our famous white boarding technique. This technique has been very beneficial for myself and many other classmates all year. We also spent a little bit of time doing a quick mini-lab that involved precipitates and net ionic reactions.

            In our introduction to Thermdynamics we discussed the difference between heat and temperature. From our discussion we concluded that heat is a measurement of the total energy that is present in the system while temperature is the measurement of the heat content of the system. In our introductory discussion, we also figured out that heat is due to the breaking or making of bonds. Temperature is also related to the transfer of heat. Lastly we learned that when heat leaves the system and goes to the surroundings it is considered an exothermic process and when heat goes into the system from the surroundings it is considered an endothermic process.

            Next we moved onto calorimetry. Here we continued to work on distinguishing between endothermic and exothermic processes. We worked on some worksheets using the formulas that we learned for the change in heat. Change in heat is equal to the mass multiplied by the specific heat capacity and the change in temperature. Calorimetry is useful to us because from this method we can find the energy change in the system by finding the energy change in the surroundings. We also talked about the enthalpy of fusion and the enthalpy of vaporization. Enthalpy of fusion has to do with the process of melting and the breaking of bonds. When vaporization occurs the rest of the bonds are broken.

            In our last topic we discussed entropy. Entropy can be defined as the possible number of microstates that are available to the system. It is represented as delta S. Entropy is greater than zero when melting or vaporizing takes place. It also occurs when the number of moles increases. Entropy can be calculated as the sum of the products minus the sum of the reactants. The last thing that involved entropy was Gibbs free energy law. This was used to figure out whether or not a process is thermodynamically favored.

            These were all of the main ideas that we covered this week. Basically they all go hand in hand with each other as they all fall under the umbrella of thermodynamics. Most of this unit had to do with math and I found that very beneficial to my personal understanding of the unit. Equations and numbers make some of the concepts easier to understand. With the equations visible to me and understanding each of the factors in the equation, I can fully realize what is going on in the process of the reaction. I would say that my participation was there this week as I asked a lot of questions pertaining to some of the problems in our worksheets. Overall, I would put my understanding with this material at about an 8/10.

Here is a video previewing a step of our lab next week.

10/21-10/25

            This week was another jam packed week of AP Chem action. 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 struggle for not only myself, but just about the entirety of our class (aside from Larkin).

            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 a struggle for me as a I only got 7 questions out of 60 right.

            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.

            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.

            That’s pretty much all we did this week. I thought that I had a good grasp on the material that we learned this week and I believe that I had a good amount of participation. For this reason, I don’t really have any questions on the material covered this week.

This week we had a lot going on in class. We worked with WebMO to create virtual representations of our molecular domain geometries so we could better visualize the shape of the atoms and build upon our knowledge of geometries that we did with the balloon and gum drop models. Basically we just built upon the main ideas that we had learned last week on VSEPR.

            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.

            Lastly, we talked a little bit about hybridization or the combination of s and p orbitals. This is the mixing of orbitals to create new orbitals that are more suitable for bonding. Hybridization only occurs in the s and p orbitals. For two bonds in the molecule there is an sp hybridization, for three bonds it is sp², and for sp³ there are four bonds. You cannot go any further than this.

            I think that I had a good grasp on the material this week and my participation was there every day. My understanding is at about an 8 and I just need more practice with the material. Other than that everything is going well.

http://www.youtube.com/watch?v=vyT5YF4UEy0

10/7-10/11

            This week in AP Chem we worked a lot more on Lewis structures. We specifically clued 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.

            Up to this point, we knew that there was a certain checklist needed for making Lewis structures. First, one must determine, from the compound, which atom is the least electronegative and place this atom as the center atom. 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. (Note: Hydrogen has a complete octet with two electrons.) We then want to place any remaining unpaired electrons around the inside atom.

            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. By doing our pogil on formal charges, we also learned that you can take unbonded electrons on the outside atom and move them down to create a bond between the inside and outside atom to change the formal charge.

            We also did another pogil on 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.

            I don’t really have any questions on what we did this week. It all connects together in my head and I have a good grasp on drawing Lewis structures. My participation was there in everything that we did this week and therefore I have a better grasp on Lewis structures than I did before. I still need to practice drawing Lewis structures to get better and better. 

9/30-10/4

                This week was a lab week in AP Chemistry. We completed 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 further our knowledge on Lewis structures. We completed a pogil on bond order and bond strength, one on resonance and VSEPR theory. We learned a lot of new main ideas from these pogils that will be very important to us.

            The first pogil we worked on was one on bond order and bond strength. Bond order occurs when you need multiple bonds to connect two atoms’ valence electrons together so they can 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 saw this from working on the pogil on bond orders. This is crucial knowledge for us moving forward and to understand what is going on in the Lewis structures that we build.

            In our next pogil we looked 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. The best example that we say was the resonance hybrid representation of benzene. You can move around the double bonds on certain C-C bonds around the central atom. The other main concept that we learned from this pogil is that as bond order increases, bond length decreases.

            In our last pogil, we worked on VSEPR theory. This theory shows us the overall shapes of molecules. We completed 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 really look like when it is bonded.

            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. We tested this 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.

            I thought I had a good grasp of the material that we worked with this week. I didn’t find it too complicated and was able to easily understand the material. My participation in all of our work was 100% except for the day that I was not present. 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.

9/23-9/27

This week was pretty slow in AP Chem. We spent the first half of the week reviewing and taking our test on stoichiometry. The test covered limiting reactants, empirical formulas, and percent yield. I thought that the test was a good challenge and a good measuring stick for myself. I know I am capable of doing better, I just have to study more and do more practice problems before the test. For the rest of the time this week we went over Lewis structures.

            So far, I have found the material that we have gone over on Lewis structures fairly comprehensible. The main ideas that we covered on Lewis structures were how to figure out which atom is the central atom and how to form the covalent bonds. To figure out which atom is the inside atom, you must determine the electronegativities of the atoms. Then, you find out which atom has the lowest electronegativity and place it in the center. Then you form covalent bonds with unpaired electrons from the outside atoms to the inside atoms. We didn’t really go over this in class but resonance and bond order was discussed in the lectures. I found these two concepts a bit more confusing but I’m hoping we work on them in class so I can gain a better understanding.

            Overall, this week was pretty light so there isn’t too much to discuss here. I found the activities that we did to gain knowledge on Lewis structures pretty straightforward and the lectures on resonance and bonding orders a bit more complex. I learned from taking the test this week that I need to work harder on doing more practice problems and studying harder to get a higher grade on the test. I would still rate my understanding on the past material covered on the test and the new material that we learned this week at about a 4 out of 5. I was able to participate fully in all of the activities we did this week and that helped me broaden my thinking about Lewis structures and how they really work.

How to draw Lewis dot structures: http://www.youtube.com/watch?v=z3F7LjTvdX0