11/4/13 Weekly Reflection

Ionic compounds and metals were the first topic of the week. Specifically, we worked on metallic solids, alloys, and the electron sea model. Next, we dealt with van der Waals intermolecular forces, including H-bonding, dipole-dipole interactions, induced dipole-dipole interactions, and London dispersion forces. H- bonding is when hydrogen is in an extremely polar bond, causing it to be nearly entirely positive and attract other, negatively charged ends of molecules in which H-bonding is present. This is the most powerful of van der Waals forces. Dipole-dipole interactions are when molecules with dipole moments are attracted to the oppositely charged ends of other molecules with dipole moments. This is the next strongest. Next is dipole-induced dipole interactions, where the dipole moment in one molecule will cause the electron cloud of another molecule to shift, inducing a dipole moment in that molecule and causing some attraction. London dispersion forces (LDF's) are the weakest intermolecular forces and are present in every substance. Because electrons are constantly moving, there will occasionally be an instant when the electrons are shifted to one side of the molecule, causing a temporary dipole moment which is then passed around the substance. We spent the rest of the week white boarding and working with water models.  

I tried very hard to participate in the learning process this week because I understood all of the material very well. I especially liked the idea that the electron cloud around any given molecule is not fixed, and that they can all be on one side temporarily, spreading an induced dipole throughout the substance. I need to work more on interacting with my group - everyone in my new group is kind of quiet, and we don't know each other that well, so it's a little awkward, and I need to work to iron that out. I was curious about surface tension. Specifically, I was wondering why, if water has a stronger adhesive force with glass than a cohesive force with itself, things can rest on the surface tension of the water. Is it just because there is a different and weaker adhesive force between water and, for example, water striders than between water and glass? Also, in the PowerPoint on cohesive and adhesive forces you said that trees could only pull water up thirty-three feet. How are trees taller than this if they can only bring water up thirty-three feet? This section was fun because now I get to consider the possible cohesive, adhesive, and intermolecular forces operating all around me.