|MadSci Network: Chemistry|
Good observation - Yes pennies do work better than nickels. But I'm afraid that you may not be working with copper, but with zinc... which still works better than nickels. This first thing is to remember that american coins are no longer made of their traditional metals (pennies - copper, nickels - nickel and dimes - silver) After 1981 pennies became largely zinc, and longer ago than that, nickels and dimes went to baser (less valuable) metals as well. But whether your pennies are primarily pre-1981 copper or 1982 and later zinc, they are still both very "active" metals. And therefore do wonderful things as batteries. What is this "active?" It has to do with how willing a metal is to part with its valence electrons. The closer to the edges, and the closer to the top of the periodic table a metal is, the more active it usually is. Further, two metals near each other will often (but not always) have similar properties. If you will go look at this periodic table: http://www.webelements.com/index.html you can see zinc (Zn) and copper (Cu) are right next to each other, and therefore have similar properties. They are also near the top and edge of their section, and are therefore quite willing to play fast and loose with their electrons (let them move around). Nickel (Ni), and iron (Fe) (another metal you may have played with) are closer to the middle of their section, and therefore their electrons are a little more closely guarded. The ability for metals to conduct electricity and/or contribute to the power of batteries also has to do with the way the electrons are stacked around the nucleus. Copper and zinc are stacked in such a way that they have very little or no "forbidden zone" so the electrons can go anywhere they want. the middle metals have a little bit bigger forbidden zone, so thier action in batteries is not so great. Finally, the non-metals have an enormous forbidden zone, so things like oxygen and sulfur don't conduct electricity at all, and make horrible batteries. To sum it all up - there are lots of reasons why some metals are better in batteries than others. I have introduced you the a few of the best known and understood. Yes some of this stuff is still under very sophisticated debate! From here I would reccomend that you get your hands on a good chemistry book and look up and read about the following: "activity" or "activity series" "Forbidden zone" "electron orbitals" "electrochemistry" and "standard electrode potential" That should give you a more thorough idea... with pictures! Good Luck, Greta Hardin
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