3. Bonding
ionic bonding
Ionic Bonding: We began Journey 3 of Honors Chemistry class by learning about Ionic Bonding. Ionic Bonding is the transfer of valence electron(s) between atoms. This bond is formed when one atom gives up one or more electrons to another atom. This type of bond results in two oppositely charged ions. One atom loses electrons to become a positively charged ion, and the other atom accepts the electrons to become a negatively charged ion. An Ionic bond is the transferring of electrons from an atom that has a low binding energy - usually a metal - to an atom that has a higher binding energy - usually a nonmetal.
Conductivity Probe: The first lab that we performed involved a conductivity probe. The goal of this lab was to design an experiment to test the conductivity of the various types of matter. The materials we used were Pure H2O, Solid Table Salt (NaCl), Aqueous Table Salt (NaCl mixed w/ pure H2O), Solid Sucrose (C12H22O11), and Aqueous Sucrose (C12H22O11 mixed w/ pure H2O) samples, a bowl, black and red wires, solder, blue LED light, and a 9 volt battery.
In this experiment, we created a conductivity probe by connecting one wire to one side of the battery, connecting other wire to other side of battery, placing blue light on the end of wire, and then sealing them with the solder. We then took each of our samples and tested them individually using our circuit. We did this by placing the one side of the wire connected to the light into a sample. We then watched to see if the sample caused the light to turn on. From our observation, we found that table salt, the solid sucrose, and the aqueous sucrose did not produce any light. We found that aqueous table salt, H2O, the inside of an orange slice, orange peal, tap H2O, and an alligator clip produced light. We concluded that all of the samples that produced light were atoms that contained ionic bonds.
Salt Water Lab: In this lab, we were asked to design and conduct an experiment that could allow us to determine the percent ionic and percent covalent compound by mass in a mixture. The materials we used were a burner, rack, bowl, scale, table salt, and water. In the experiment, we combined the salt and water and placed it into the bowl. We then weighed the bowl, recorded the information, and placed over heat. We then boiled it until the water appeared to be totally evaporated. Once the water was evaporated, we weighed the dish that contained the remaining salt. Finally, we calculated moles of water compared to salt so that we could determine what percent of the compound was ionic and what percent was covalent.
From the weights we recorded, we determined that the compound was made up of 15.46 percent Ionic bonds and 84.54 percent covalent bonds.
Mystery Ionic Compounds: The goal of this next lab was to learn how to identify unknown ionic compounds. In the lab, we were asked to determine the identity of the 6 unknown Ionic compounds from the possible choices presented (displayed below to the left). The materials we used were small bulb pipettes, microplates, and different compound mixtures. To perform the lab, we used the proper mixing technique that Ramsey taught our class. We transferred the different mixtures into the micro plates. We then observed the reactions. Ramsey provided us with a chart of the possibilities of the different type of reactions that could occur and the correlating compound (described below to the right) . From our observations, we were able to identify each ionic compound.
Unknown Compound Possibilities:
Copper (II) Nitride, Calcium Chloride, Sodium Carbonate, Lead (II) Nitride, Potassium Iodide, Hydrogen Acetate
Mixing Possibilities: Lead (II) Iodide = Cloudy Yellow, Lead (II) Carbonate = Cloudy White , Lead (II) Chloride = Milky White , Hydrogen Carbonate = Bubbles, Copper (II) Carbonate = Cloudy Blue
covalent bonding
Covalent Bonding: Covalent Bonding is the sharing of electron pairs between atoms. This bond occurs when pairs of electrons are shared by atoms. The atoms bond so that they can gain stability. They gain stability by filling their outer electron shell. Covalent bonds are bonds that are formed from shared electrons between atoms who both have relatively high binding energies - usually a nonmetals.
Covalent vs Ionic Bonds: Next, we reaffirmed why we know compounds are Covalent and not Ionic. The two main reasons are the following. Ionic bonds are the transferring of electrons from an atom that has a low binding energy (usually a metal) to an atom that has a higher binding energy (usually nonmetal). Covalent bonds are shared electrons between atom that both have relatively high binding energies (usually nonmetals).
Shapes of Molecules: In this portion of Journey 3 of Honors Chem, we learned about the shapes of molecules. We used the the Valence-Shell Electron-Pair Repulsion (VSEPR) model to understand the approximate shapes and how the shape of a molecule can be predicted. We also learned that understanding how to draw a Lewis structure will help predict the three-dimensional shape of a molecule. It is important to know that the shape of a molecule affects its physical properties and how it interacts with other molecules.
Lewis Structures: In this portion of the class, we learned about Lewis structures. Lewis structures are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that the molecule may contain.
Steps used to draw Lewis Structures: We learned that we need to follow these steps to draw a Lewis Structures. (1) Find the total number of valence electrons. (2) Find the number of electrons needed to make the atoms stable. (3) Choose a central atom. (4) Draw a skeletal structure. (5) Place electrons around outside atoms. (6) Place remaining Electrons around the central atom. Example of a Lewis Structure is to the left.
*We also learned the formula for determining the number of bonds. It is the number of electrons an atom wants - minus the number of electrons an atom has - divided by two.
Molecular Geometry: Images of molecules can be shown by their molecular geometry of covalent bonded molecules. These shapes and examples can be seen below.
reflection
I learned so much from Journey 3 of Honors Chemistry. I enjoyed learning the material and performing lab experiments. These were interesting concepts and I feel that I understand them for the most part. Ramsey is such an amazing teacher, and I learn really easily from him and the way he teaches. I love the class. As the final phase of our class concluded, I prepared for the test. I did this by reviewing class notes, my labs, and the homework.
Overall, I learned a lot of information and I continue to enjoy honors chemistry.