Bismuth is a rare metal that we don’t see much in everyday life. But this shiny metal, which is found near the bottom of the periodic table, has some really cool abilities. One of the coolest things about bismuth is that it can float between two magnets. This happens because bismuth is pushed away so strongly by the magnets that it seems like it’s floating.
But why does bismuth get pushed away from magnets so strongly?
Eric Riesel, a scientist who studies materials affected by magnets at MIT, says it’s because of the kind of magnetism that bismuth has. All materials have magnetic properties because of a tiny part of their atoms called spin. This spin can only point in two directions: up or down. The way all these spins come together in a material decides what kind of magnetism it has.
“Many people know about ferromagnets, like iron, which are permanent magnets where all the spins are lined up in the same direction,” Riesel explained to Live Science.
“But there are also anti-ferromagnets where the spins point in opposite directions,” he added.
There are also two other types of magnets: paramagnetism and diamagnetism. “In paramagnets, when you put a magnetic field, the spins in that material will line up with the field depending on how strong it is,” he said. Diamagnets, on the other hand, push against the magnetic field, making it go in the opposite direction and repelling it.”
Bismuth behaves strangely when it comes to magnetism. Normally, how a material behaves magnetically depends on how its electrons are arranged and the direction they spin. Electrons move around the nucleus in layers called shells, which are divided into smaller levels called orbitals.
Usually, materials that repel magnets (diamagnetic) have a full set of orbitals. This means the electrons are paired up, with one spinning up and the other spinning down, which cancels out their magnetic effect. On the other hand, materials that are attracted to magnets (paramagnetic) usually have some unpaired electrons in their orbitals, allowing them to align their spins in the same direction.
Bismuth belongs to Group 15 in the periodic table.
While its s, d, and f orbitals are full, its p orbitals have only three out of a possible six electrons. So, theoretically, bismuth should behave like a paramagnet. However, because it’s in row six of the periodic table, bismuth also has some unique properties because of its heavy atoms.
“Chemical elements beyond the f-block in the periodic table have electrons moving around the nucleus very quickly,” explained Ira Martyniak, another magnetic materials chemist at MIT. “Because of this, the 6s and 6p orbitals, which are the outermost layers, shrink and get closer to the nucleus. This leads to some strange physical and chemical properties.”
These effects caused by relativity explain many of bismuth’s surprising traits, like its unusual ability to conduct electricity without resistance (superconductivity), its very low melting point (520.7 degrees Fahrenheit, or 271.5 degrees Celsius), and the strange shapes its crystals form. The unexpected diamagnetism of bismuth is just another example of this.
“Even though bismuth has some unpaired electrons in its 6p orbital, because of the way the 6s and 6p levels shrink due to relativity, the paramagnetism from those electrons gets weakened. Instead, bismuth mostly shows diamagnetism because of its closed shells and large size,” Martyniak explained.
Diamagnetic materials are useful in many ways, like helping create electricity in copper coils and in the tracks of high-speed maglev trains. Although bismuth itself is too heavy for everyday use, its strong diamagnetism makes it valuable in things like superconductors and quantum computing.
