Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A very peculiar magnetic effect (chemist yells help! )

  1. Nov 10, 2005 #1
    A very peculiar magnetic effect (chemist yells "help!")

    Hello all,

    Today I was approached by a chemist who teaches A/P and honors physics at the high school. He showed me an experiment the class had been doing on transition metals.

    This was the setup:

    He placed a neodymium magnet on a very sensitive mass balance and weighed it. Around it he put a roll of thick paper (which wasn't touching the balance plate, so it would not affect the weight reading). Then on top of the roll he put a small frame made of wood, and finally a glass vial on the frame containing samples of various ions which all had Chloride as as the "other half." The metals were Mn (2+), Fe (2+), Co (2+), and Zn (2+).

    He expected to find the magnet slightly attracted to the transition metals, because they were positive ions and lack 2 electrons. And he found that for *most* of the metals the magnet was indeed attracted, and the mass read that attraction as the magnet becoming lighter as it was drawn toward the frame.

    But then he put in the Zinc, and found the opposite effect -- the magnet was repelled! No matter how he turned the magnet (he even flipped it) or adjusted the sample, the same result obtained. For some reason, Zinc has this property.

    He thinks it may have something to do with the orbitals. All the other metals have two unfilled slots (an "unbalanced" electron in the orbital), while Zinc 2+ loses electrons (both of them) from one of its "s" shells, and therefore has no unpaired electrons.

    But he's stumped, and so am I. Does anyone have an idea about how to answer the question as to why Zinc behaves so differently when exposed to a magnetic field?

    Thanks for the help!
  2. jcsd
  3. Nov 10, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Your chemistry friend just rediscovered for himself, the difference between diamagnetism and paramagnetism, and the cause of these effects.

    Among all the ions he tried, Zn2+ is the only one without unpaired electrons in the valence shell. This makes the ion diamagnetic. All the other ions (Co2+, Fe2+, Mn2+) have 3 or more unpaired electrons and are all paramagnetic.

    This is why the different response in the mass balance.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook