10-28-13

This week, we started out with review for our test. We asked a lot of questions, especially about the Lecture Chemical Bonding packets, and used class time to review.
After taking the test, it was Mole Day. We had really good cookies and hot chocolate.

  

We received a packet on Paintball and wrote about hydrogen bonding and polarity. We learned about how water’s polarity is due to the differences in electronegativity between oxygen and hydrogen. In water there is a region of partial negative charge on the side of oxygen, and a partial positive charge on the side of hydrogen. The molecules shape of bent and the polar bonds make the molecule polar overall. Hydrogen bonds occur when a hydrogen atom attaches to a small and highly electronegative atom, in this case Oxygen, in the vicinity of an atom with nonbonding electron pairs. Hydrogen bonds are the strongest of the intermolecular forces (but not as strong as covalent or ionic bonds). Hydrogen bonds are about 1/15th the strength of a covalent bond. The hydrogen bonds in water are what hold the molecule together.

We then began learning about ionic bonds, which was mostly a review. Ionic bonds are formed between two atoms when the atoms involved transfer one or more electrons to produce two charged species - positive (cation) and negative (anion). Atoms with loosely held electrons tend to form positive ions, but those who can hold additional electrons relatively strongly tend to form negative ions.

We learned about metals as well. Some properties of metals are that they have a shine or luster, can conduct heat and electricity, they're ductile, and they are malleable. Nonmetals do not have these properties - they're typically poor conductors of heat or electricity, and they aren't malleable or ductile. Electronegativity is much lower for a metal than for a nonmetal as well. In metals, the bonding is different from both covalent and ionic bonding. The electrons in their bonds are localized meaning they either are shared by a pair of atoms or they are associated with one of the two species involved in the bonding interaction. Valence electrons on a metal atom are shared with many neighboring atoms, not just one. These valence electrons are delocalized. The force of attraction between the positive metal ions and the sea of mobile negative electrons forms a metallic bond that holds these particles together.

This week, I'd rate my understanding of our topics at about a 9. It's mostly review with the ionic and covalent bonding and I feel like I understand the metals so far. I was able to help some of my classmates at my table especially with the Ionic Bonds POGIL because most of it was information that I already knew. Although, I was surprised when we were looking at the model of NaCl, that the atom for Na was the smaller particles and not actually the bigger ones. So far, I'm enjoying this topic and I hope I do better on this test than I did on the last one.

10-21-13

This week, we started out with a lecture quiz on sigma and pi bonding, then learned about hybrid orbitals, and had time in class to work on our WebMO.

Sigma bonds are characterized by head to head overlaps and cylindrical symmetry of electron density about the internuclear axis. Pi bonds are characterized by side to side overlaps and electron density above and below the internuclear axis. Single bonds are always sigma bonds because sigma overlaps are greater, which makes a stronger bond and more energy lowering. Double bonds contain one sigma and one pi bond. Triple bonds form with 2 pi bonds and 1 sigma bond. Resonance structures are used to more accurately reflect the structure of the molecule or ion.

We also learned about hybrid orbitals. The electron pairs around the central atom in a molecule are said to be in a set of orbitals (domains) that are hybridized from the usual set of atomic orbitals (s,p,d) for the atom. If one s-orbital and one p-orbital are used-2 hybrid orbitals called sp hybrid orbitals are made. With sp hybrid orbitals there are 2 hybrid orbitals in each set, one s, and one p, 180º between orbitals, and they are linear. With sp2 hybrid orbitals there are 3 hybrid orbitals in each set, one s, and two p, 120º between orbitals and they are trigonal planar. With sp3 hybrid orbitals there are 4 hybrid orbitals in each set one s, and three p, 109.45º and they are tetrahedral. 

We worked a lot on our WebMO diagrams making each of the 13 molecules on the website, finding their angles, dipole moment, and electrostatic potential map. 

My understanding of the two new topics that we learned this week is probably a 9.5. I definitely understand sigma and pi bonds, and I understand hybrid orbitals and could teach them to my classmates if needed. For the test on Tuesday, throughout the week I felt very lost and confused with each of the subjects we had previously learned (such as molecular shapes, bonding, and polarity), but I feel that after doing the WebMO project and the VSEPR Balloon lab report I really understand more of it. The hotpot quizzes really helped, and I took a lot of screenshots of the questions I didn't understand. After studying and working on the projects this weekend I'm beginning to feel a little bit more comfortable about the test on Tuesday. I think that the more I study Monday night, I'll be completely ready for the test on Tuesday....hopefully. 

10-14-13

This week, we started out by finishing up the VSEPR structures, then more Lewis structures, and Formal charges. We use formal charges to make correct Lewis structures which can then be used to identify VSEPR structures.
We started out finishing up the VSEPR theory lab. We used balloons to determine the shape and angles of molecules. Electron domains are a region where electrons are most likely to be found. Our group used balloons to make SF6 and BrF5. There are two types of of VSEPR structures. One is Electron Domain geometry which is based off how many electron domains there are per central atom. We learned that the 5 possible shapes that can be formed by electron domains: Linear, Trigonal Planar, Tetrahedral, Trigonal Pyramidal, and Octahedral. Linear structures contain two electron domains, trigonal planar have three electron domains, tetrahedral have four electron domains, trigonal bipyramidal have five electron domains and octahedral have six electron domains. The second type of structure is molecular domain geometry. Molecular domain geometry structures are based on how many actual bonded atoms there are connected to the central atom. If all of the electron domains of a central atom are bonded to another atom, then the molecular domain geometries are exactly the same as the electron domain geometries. 

We used balloons to create models of electron domain geometries and used gummies to create molecular geometries. These structures made out of the different items made it a lot easier to visualize the shape of the molecular structure, but I feel like the balloons were a little easier to use because the gummies kept melting out of place. 

We also learned a lot about how to make Lewis structures by using formal charges. Formal charges are assigned to atoms in molecules according to a set of rules. 1. Nonbonding electrons are assigned to the attached atom. 2. Shared electrons are evenly divided between the bonded atoms. A Lewis structure is not complete unless the formal charges are indicated (except "0" is not used). Formal charges by doing formal charge = core charge - number of assigned electrons. The best Lewis structures are the ones with the lowest formal charges. Formal charges greater than positive or negative 1 are never found in good Lewis structures. We also learned that atoms in the 3rd, 4th, and 5th periods can have extended octets, meaning that the sum of the bonding and lone-pair electrons can be greater than 8. 

This week I'd give my understanding on this subject about a 7. I really understand the idea of formal charges, and how to find them. It was easy for me to explain to my classmates on how to find it and how to use it. I also understand the extended octets on the 3rd, 4th, and 5th periods, and helped to remind my tablemates that when we were whiteboarding some of the atoms could have more than eight atoms. The reason my understanding of the topics is at a higher rating this week is because of the molecular and electron domain geometries. I'm still unsure about how to identify the different shapes of each molecule. My questions for this week would be how to identify the angles in the electron and molecular domain geometries? I hope this week I can understand electron domain and molecular geometries.

10-7-13

This week we started learning more and more about Lewis structures and molecules. We started with bond order and bond strength. Bond energy is defined as the energy required to sever the bond that holds two adjacent atoms together in a molecule. It's usually expressed on a molar basis. Bond order tells the type of bond between two atoms. For example, two atoms with a single bond has a bond order of 1. Two atoms with a triple bond have a bond order of 3. The higher the atomic number, the higher the bond order. Triple bonds have the highest amount of strength, while single bonds have the lowest amount of strength. Bond length is defined as the distance between the nuclei of two bonding atoms. The shorter the bond, the stronger the bond because there is more energy the shorter the bond.

We also did a lab to try and determine the percentage by mass (mass percent) of copper in brass screws or any other brass item. It was important during the lab to use extreme safety because of the concentrated nitric acid. Concentrated nitric acid is corrosive and will attack and destroy metals, plastics, and proteins. Skin contact with the acid would discolor the skin for days. The gas that forms from it is a toxic, reddish-brown gas of NO2. The nitric acid addition was performed under the fume hood and we all made sure we wore goggles. The nitric acid was added to the brass screw and left in the beaker over night. The next day, after the screw had dissolved, our group used the visual comparison test to determine the concentration of the unknown solution. The two test tubes of the reaction solution, and the unknown solution were placed on top of a white sheet of paper and then the intensity of the color of each solution was compared and the solution was removed or added until the colors finally matched. Then, after measuring the depth of each solution we used the equation (Molarity1)(Depth1) = (Molarity2)(Depth2). 

On Friday, we started the VSEPR Theory Lab and used balloons to determine the shape and angles of molecules. Electron domains are a region where electrons are most likely to be found. Our group used balloons to make SF6 and BrF5. This week, I'd give my understanding on this subject about an 8. I really understand the relationship between bond order, bond length, and bond energy. I really enjoyed the lab with watching the brass dissolve, and the colored gas come from the reaction between the two elements. The VSPER lab (that's still not done) was also really fun with the balloons, although I probably got a little carried away with the balloons. I still have questions on how to name the shapes that came from the gum drop models? I don't quite understand the octahedral and square pyramid part, so I'm hoping this week I'll get a better understanding of it.