List of Paramagnetic Atoms

••• ktsimage/iStock/GettyImages

All atoms respond in some way to magnetic fields, but they respond differently depending on the configuration of the atoms surrounding the nucleus. Depending on this configuration, an element can be diamagnetic, paramagnetic or ferromagnetic. Elements that are diamagnetic – which is actually all of them, to a degree – are weakly repelled by a magnetic field, while paramagnetic elements are weakly attracted and can become magnetized. Ferromagnetic materials also have the ability to become magnetized, but unlike paramagnetic elements, the magnetization is permanent. Both paramagnetism and ferromagnetism are stronger than diamagnetism, so elements that exhibit either paramagnetism or ferromagnetism are no longer diamagnetic.

Only a few elements are ferromagnetic at room temperature. They include iron (Fe), nickel (Ni), cobalt (Co), gadolinium (Gd) and – as scientists recently discovered – ruthenium (Ru). You can make a permanent magnet with any of these metals by exposing it to a magnetic field. The list of paramagnetic atoms is much longer. A paramagnetic element becomes magnetic in the presence of a magnetic field, but it loses its magnetic properties as soon as you remove the field. The reason for this behavior is the presence of one or more unpaired electrons in the outer orbital shell.

Paramagnetic vs. Diamagnetic Elements

One of the most important discoveries in science during the last 200 years is the interconnectedness of electricity and magnetism. Because every atom has a cloud of negatively charged electrons, it has the potential for magnetic properties, but whether it displays ferromagnetism, paramagnetism or diamagnetism depends on their configuration. To appreciate this, it's necessary to understand how electrons decide which orbits to occupy around the nucleus.

The electrons have a quality called spin, which you can visualize as direction of rotation, although it's more complicated than that. Electrons can have "spin-up" (which you can visualize as clockwise rotation) or "spin-down" (counterclockwise). They arrange themselves at increasing, strictly defined distances from the nucleus called shells, and within each shell are subshells that have a discrete number of orbitals that can be occupied by a maximum of two electrons, each having opposite spin. Two electrons occupying an orbital are said to be paired. Their spins cancel and they create no net magnetic moment. A single electron occupying an orbital, on the other hand, is unpaired, and it does result in a net magnetic moment.

Diamagnetic elements are those with no unpaired electrons. These elements weakly oppose a magnetic field, which scientists often demonstrate by levitating a diamagnetic material, such as pyrolitic graphite or a frog (yes, a frog!) over a strong electromagnet. Paramagnetic elements are those that do have unpaired electrons. They give the atom a net magnetic dipole moment, and when a field is applied, the atoms align with the field, and the element becomes magnetic. When you remove the field, thermal energy intervenes to randomize the alignment, and the magnetism is lost.

Calculating Whether an Element Is Paramagnetic or Diamagnetic

Electrons fill shells around the nucleus in a way that minimizes net energy. Scientists have discovered three rules that they follow when doing this, known as the Aufbrau Principle, Hund's Rule and the Pauli Exclusion Principle. Applying these rules, chemists can determine how many electrons occupy each of the subshells surrounding a nucleus.

To determine whether an element is diamagnetic or paramagnetic, it's necessary only to look at the valence electrons, which are those that occupy the outermost subshell. If the outermost subshell contains orbitals with unpaired electrons, the element is paramagnetic. Otherwise, it's diamagnetic. Scientists identify the subshells as s, p, d and f. When writing electron configuration, the convention is to precede the valence electrons by the noble gas that precedes the element in question in the periodic table. Noble gases have completely filled electron orbitals, which is why they are inert.

For example, the electron configuration for magnesium (Mg) is [Ne]3s2. The outermost subshell contains two electrons, but they are unpaired, so magnesium is paramagnetic. On the other hand, the electron configuration of zinc (Zn) is [Ar]4s23d10. It has no unpaired electrons in its outer shell, so zinc is diamagnetic.

A List of Paramagnetic Atoms

You could calculate the magnetic properties of each element by writing out their electron configurations, but fortunately, you don't have to. Chemists have already created a table of paramagnetic elements. They are as follows:

  • Lithium (Li)
  • Oxygen (O)
  • Sodium (Na)
  • Magnesium (Mg)
  • Aluminum (Al)
  • Potassium (K)
  • Calcium (Ca)
  • Scandium (Sc)
  • Titanium (Ti)
  • Vanadium (V)
  • Manganese (Mn)
  • Rubidium (Rb)
  • Strontium (Sr)
  • Yttrium (Y)
  • Zirconium (Zr)
  • Niobium (Nb)
  • Molybdenum (Mb)
  • Technetium (Tc)
  • Ruthenium (Ru) (recently found to be ferromagnetic)
  • Rhodium (Rh)
  • Palladium (Pd)
  • Cesium (Cs)
  • Barium (Ba)
  • Lanthanum (La)
  • Cerium (Ce)
  • Praseodymium (Pr)
  • Neodymium (Nd)
  • Samarium (Sm)
  • Europium (Eu)
  • Terbium (Tb)
  • Dysprosium (Dy)
  • Holmium (Ho)
  • Erbium (Er)
  • Thulium (Tm)
  • Ytterbium (Yb)
  • Lutetium (Lu)
  • Hafnium (Hf)
  • Tantalum (Ta)
  • Tungsten (W)
  • Rhenium (Re)
  • Osmium (Os)
  • Iridium (Ir)
  • Platinum (Pt)
  • Thorium (Th)
  • Protactinium (Pa)
  • Uranium (U)
  • Plutonium (Pu)
  • Americium (A)

Paramagnetic Compounds

When atoms combine to form compounds, some of those compounds can also exhibit paramagnetism for the same reason that elements do. If one or more unpaired electron exists in the compound's orbitals, the compound will be paramagnetic. Examples include molecular oxygen (O2), iron oxide (FeO) and nitric oxide (NO). In the case of oxygen, it's possible to display this paramagnetism using a strong electromagnet. If you pour liquid oxygen between the poles of such a magnet, the oxygen will collect around the poles as it vaporizes to create a cloud of oxygen gas. Try the same experiment with liquid nitrogen (N2), which is not paramagnetic, and no such cloud will form.

If you wanted to compile a paramagnetic compounds list, you would have to examine electron configurations. Because it's the unpaired electrons in the outer valence shells that bestow paramagnetic qualities, compounds with such electrons sould make the list. This isn't always true, though. In the case of the oxygen molecule, there are an even number of valence electrons, but they each occupy a lower energy state to minimize the overall energy state of the molecule. Instead of an electron pair in a higher orbital, there are two unpaired electrons in lower orbitals, which makes the molecule paramagnetic.

References

About the Author

Chris Deziel holds a Bachelor's degree in physics and a Master's degree in Humanities, He has taught science, math and English at the university level, both in his native Canada and in Japan. He began writing online in 2010, offering information in scientific, cultural and practical topics. His writing covers science, math and home improvement and design, as well as religion and the oriental healing arts.

Dont Go!

We Have More Great Sciencing Articles!