This activity is a great one for interleaving ideas about atomic structure, how ions are formed and the new idea of paramagnetism in transition metals. My kids also found it surprising that these ionic compounds respond to a magnetic field at all!
HOW TO SET IT UP
- Cut the ends of plastic pipettes.
- Add small amount of CuCl2, NiCO3, FeSO4, MnO2, ZnCl2 to each pipette. (or transition metal salts of your choice!)
- Tape the pipettes back together and tie with string and tape to a meter ruler so that the pipettes can move freely.
- To test magnetic properties approach each pipette slowly with a neodymium magnet (it doesn’t work with a iron magnet/less strong magnetic field)
“Rank them in order of how attracted they will be to a magnetic field”
“Draw diagrams to justify your predictions”
Predicting magnetic properties rely on a basic understanding of ferromagnetism, paramagnetism and diamagnetism.
Ferromagnetism: Only exhibited by iron, cobalt and nickel metals (and some alloys of these metals), a very strong response to a magnetic field and an ability to maintain the magnetism once the magnetic field has been removed. Also you only get strong repulsion between ferromagnetic materials.
Paramagnetism: Species with unpaired electrons exhibit very weak attraction to a magnetic field. Does not maintain the magnetism once the field is removed.
Diamagnetic: Species with all paired electrons exhibit very very very very weak repulsion to a magnetic field. Definitely not visible with the neodymium magnets we have at my school!
All of these transition metal ions will be either paramagnetic or diamagnetic so let’s look at their 3d electronic configurations (all of the 4s electrons are lost in the formation of these ions). This is a great review of the atomic structure unit!
Cu2+ has a configuration of 3d9 – so it has one unpaired electron in its 3d sub level.
Ni2+ has a configuration of 3d8 – so it has two unpaired electrons in its 3d sub level.
Fe2+ has a configuration of 3d6 – so it has four unpaired electrons in its 3d sub level.
Mn4+ has a configuration of 3d3 – so it has three unpaired electrons in its 3d sub level.
Zn2+ has a configuration of 3d10 – so it has no unpaired electrons in its 3d sub level – making it not a transition metal at all!
The ions with the most unpaired electrons will exhibit the highest paramagnetism (more electrons that can be aligned with the magnetic field) and the strongest attraction to the magnetic field.
Highest to lowest attraction should therefore be observed as:
Fe2+> Mn4+ >Ni2+ >Cu2+ > Zn2+
Any other suggestions/feedback greatly appreciated!