Week 7

This week in AP Chemistry we reviewed and were tested on covalent bonding. Some of the topic areas in this unit were the Lewis structures formed by these bonds, the electron domain geometry and molecular domain geometry around the central atoms or any other particular atoms and the hybridization of s- and p-orbitals along with the very recent debate over the hybridization of the d-block orbitals and their effects. In order to review for the test we utilized a new tool on the class Moodle called a TaskChain, a series of quizzes in which you must achieve a 90 percent or higher score, given partial credit for correct second and third answers, in order to move on to the next in the series. This simple quiz offered me three significant advantages. First, it offered me more peace-of-mind, knowing that I was able to pass all nine with at least an A grade on my first attempt, even when clicking mistakes were accounted for. Second, this way of reviewing was perfect for the teacher to show me the types of questions that would be on the test and what they would generally look like. Third, these quizzes were extensive and covered nearly all material, reminding me of any relationships or topic areas that may have slipped my mind over the course of the few weeks spent since the previous test.

After the covalent bonding test, on Mole Day, we were assigned to read a passage about polarity and its significance in paintball and then write an essay on what polarity is, including facts, definitions and quotations. Polarity was introduced to us in the previous unit, with dipole moments, being the partial charges on each side of a molecule pointing in a specific direction with a specific magnitude measured in Debye. This article carried this information over as well as introducing the significance of polar molecules in chemistry. The most common of these molecules, water, lines up end-to-end, positive-to-negative because the liquid molecules are allowed to slip passed each other and opposite charges attract (See link below for polarity determination help). The contact between the positive and negative ends of the molecules form polar bonds. the most common type of this bond is the hydrogen bond, between a hydrogen atom and another oppositely charged atom. This concept relates to the covalent bonding we just finished in that atoms are brought together because of charges dealing with electrons. This most significant difference in these different types of bonds is that polar bonds do not share the electrons in any way and are much weaker as a result.

A paintball match beginning

Polar bonds are what allow other polar substances to dissolve in water. The significance of this was shown in the article we read, which mentioned how scientists who were developing new types of paintballs looked for a substitute for the old paint that would be water soluble and therefor much easier to wash for the players. Applying this change to the game of paintball made its popularity skyrocket, showing how little innovations involving chemistry can improve all the different things that we do in our lives.

Toward the end of the week we were briefly introduced to the next subject of ionic bonds and their properties that can be readily determined from given information. The most important principle was that the shorter the length of an ionic bond, the more energy is released. From this you can take that the atomic radii of the elements bonded are connected to the energy of the bond. Then, knowing the law of the conservation of energy, it is logical to conclude our next idea, that boiling points increase as bond length decrease. This is because more energy was released when the bond was formed, and as a result more energy is required to pull them apart when it enters its gaseous state.

Polar molecule determination summary:
http://users.stlcc.edu/gkrishnan/polar.html