Week 4

This past week in AP Chemistry, we started out with new material on the Lewis structures of atoms. Using POGILs, we learned about the characteristics of the covalent bonds that make up many molecules in the real world. A covalent bond forms between any two separate atoms that share a pair of electrons in order to follow the octet rule. Bond order is the number of pairs of electrons shared between two atoms in a particular bond, specified as single, double or triple and depicted in a Lewis structure as one, two or three lines, respectively. Bond order can be in a theoretical form based on the information from the Lewis structure in which it will have a whole number value, or an experimentally calculated value with any number of decimal places. The bond energy/strength of a particular bond is the energy required to sever the covalent bond and is most often measured in kilojoules per mole (kJ/mol). Calculated bond length is the distance of the bond, being the distance between the nuclei of each atom involved, typically measured in picometers.

With these POGILs focusing on bond order and strength we also learned about the relationships between each of the characteristics of covalent bonds. As the bond order of a bond increases, the bond energy also increases because more electrons are being shared and must be broken apart. Similarly, as the bond order between the same two atoms increases, the bond length decreases because of the increases attractive forces between the two. Conversely, as bond length increases between  two atoms, the bond energy decreases due to the effects of coulomb's  law relating distance to electrical force. Additionally, bond length is strongly influenced by the relative size of the atomic radii of the bonded atoms (see link below for more detail and available practice.

All together, many of my ideas have changed in regard to the covalent bonds that make up many of the molecules I am so familiar with. Previously, I had never considered that there may be a relationship between the properties of individual atoms and how they form bonds with each other. Furthermore, I had not thought that many of the characteristics of these bonds would allow you to predict how to draw its Lewis structure or predict its many molecular abilities and how the Lewis structure or its properties could be used to find the characteristics of these bonds. In summary, nearly all pieces of information related to Lewis structures can be used to find many other characteristics of the situation.

The reaction of nitric acid and brass

In class this week we began our second experiment, trying to determine the percent of copper by mass of a piece of brass, an alloy of copper and zinc. The way that we intend to calculate this value is through measuring the absorbance of light by the solution of the brass and nitric acid we added as well as the absorbance of a solution of known concentration of copper to find a calibration curve to use to find the original concentration of copper.



Extensive overview of bond characteristics and practice:
http://s-owl.cengage.com/ebooks/vining_owlbook_prototype/ebook/ch8/Sect8-3-a.html

Working on the experiment