Dr. Finnan
SG Chem 2
10/25/15
We finished last week with our Unit 5 test, so this week we began Unit 6, which is all about the internal structures of particles. We looked at J.J. Thomson and his experiments with cathode rays. Then, we did our own experiment with sticky tape to understand the interactions it had with other materials. After that we tested the conductivity of different elements and compounds. Then, we went deeper by studying what was happening to the sticky tape as it interacted with the other materials and how its charge was affected. We also observed the electrolysis of CuCl2. To end the week we started looking at the composition of compounds that are solids that don't conduct electricity and found patterns in their equations.
J.J. Thomson did experiments with cathode rays in the late 1800s. Cathode rays are beams of electrodes emitted from the cathode of a high-vacuum tube. We looked at three different experiments that he performed. In the first one, Thomson directed a beam at an electrometer and tried to separate the evidence of charge from the path of the beam. He found that cathode rays deposited an electric charge, and he found that he could bend the rays with a magnet. From this first experiment, he ultimately discovered that the charge was negative and cannot be separated from the rays. In the second experiment, Thomson tried passing the cathode ray through an electric field. When the ray beam passed through the electric field it bent. From this he concluded that cathode rays are charges of negative electricity carried by particles of matter. In the third experiment, Thomson did some careful measurements on how much the path of the cathode ray was bent in a magnetic field and how much energy was carried. Thomson was able to describe the mass/change ratio of the cathode particles. Thomson also came up with an amazing result from this experiment, he found that the mass-change ratio of cathode rays is far smaller than that of a charged hydrogen. This means that cathode rats either carry an enormous charge or are extremely light relative to their charge. From these experiments Thomson presented three hypotheses, only two of which were accepted as true. From those two a model of the atom was made, know as the Plumb Pudding model. This model will help us to understand the internal structures of particles.
In the sticky tape lab we took a piece of tape and folded it, making a bottom half and then doing the same to make a top half. Then, we stuck the pieces of tape together and pulled them apart quickly to give them a charge. After that, we observed how the different pieces of tape interacted with each other and with paper and aluminum foil. We found that the top and bottom pieces were attracted to each other and the top and bottom tape both attracted the foil and the paper, but the top tape repelled itself and the bottom tape repelled itself. From this we determined that the top tape was positively charged, the bottom tape was negatively charged, and the paper and foil were both neutral. Ultimately from this lab we learned that positive and negative things are attracted to each other, two positive things repel each other, to negative things repel each other, and both positive and negative things are attracted to neutral things.
This week we used Dr. Finnan's homemade conductivity testers to test the conductivity of different elements and compounds. We found that all metals and compounds with metals in them conduct electricity. Then, we discussed as groups about what we thought the reason was for the different things that do conduct electricity. Our group concluded that metals conduct because they have free electrons that flow easily and ionic compounds (a metal and a non-metal bonded together) conduct because they have free ions that move easily.
To end the week we started looking at different compounds and their particle drawings and formulas. We were supposed to then look at patterns between the different compounds, but that's where we ended and I couldn't and still don't really understand what kinds of patterns I'm looking for. We also watched the electrolysis of CuCl2 and wrote down our observations as bubbles formed on the positive side, it smelled like a pool, and the bottom of the copper rod on the negative side began turning pink. After a little longer it continued to smell like a pool, the pink spread, and there were bubbles on both sides. Overall, this unit is very interesting and so far I like what we're learning.
No comments:
Post a Comment